StarTraX - Re-live your trip in Google Earth

How to use StarTraX - a comprehensive description of the features of StarTraX

Getting Started Getting StarTraX loaded and ready to replay your track file will be your first priority.

Controlling the replay How you use all the buttons and controls that allow you to manage your track replay.

Making the replay realistic Some of what goes on "behind the scenes".

Track Information A reference section about the information available about your track.

Gliding features If your sport involves un-powered flight then this section will be of interest to you.

Usability This section brings together a bunch of features that have been developed to make StarTraX easy and intuitive to use.

Release History This is where we document its development.

Thanks to the assistance of some dedicated volunteers who have undertaken a major translation task, StarTraX now operates in a range of languages. You can see the fruit of their labo(u)rs by clicking on the following flags :

Getting Started

Notes for the new "web version" of StarTraX



StarTraX runs on "standard" Apple Mac and Windows computers and laptops using some additional software tools from established international companies. If the software is not already installed on your computer, you will be guided through the installation when required.


  • Computer:
    • Apple Mac running OSX 10.6 ("Snow Leopard") or later.
    • Windows PC running Windows XP SP2, Vista, Windows 7 or later.
    • It doesn't run on smart phones (Android, iPhone, Blackberry etc), "tablets" or Linux computers because even though Google Earth runs on these platforms, the Google Earth browser Plugin (see below) has not yet been released.
  • Peripherals:
    • Screen: Resolution of 1280 x 1024 or greater.
      It will run on smaller screens with lower resolution but you may have trouble navigating the controls.
    • Mouse: two-button mouse preferably with a scroll wheel.
    • Internet access: Cable or ADSL quality broadband is required to download the detailed imagery from Google Earth.
  • Installed software:
    • Browser: StarTraX runs inside your browser.
      • On Apple Mac, the preferred browser is Safari Version 4 or later.
      • Windows PC, the preferred browser is Windows Explorer 9 or later.
      • On both platforms it will run in recent versions of Chrome and Firefox, but the animation performance is much reduced. It doesn't run in any other browsers (such as Safari on the PC, or Opera) because the GEPlugin is not supported in these browsers.
    • Google Earth plugin for browsers (GEPlugin) version 6.1 or later provides the amazing 3D visualization of your GPS tracks. It is available from here.
    • Java JVM Version 6 (1.6) or later, from Oracle is used to allow StarTraX to open track files from your computer's disk drive. It is available from here.

Security and privacy

Access to your data

One of the software tools you will be installing is "Java", which gives StarTraX access to the data on your disk drive. When you use Java to open a file you will be asked to agree to a number of things relating to security and certificates that you may never have thought about in the past but which are really quite important.
We personally assure you that we have no interest in damaging your computer or stealing your personal information. You have accessed StarTraX through our web site, and you can contact us at [email protected] to verify our bona fides.

Collection of data

In our continuing efforts to improve StarTraX, we collect information about which version of software you're using to access StarTraX and statistics about which StarTraX features you use.

The following description was written for the previous version of StarTraX which ran as a desktop application on Windows PC only. We are in the process of updating the notes.

All of the features (well, nearly all, and some great new features!) described below are available in the web version, but their appearance may be different and they may be located in a different position.
Please bear with us during the transition.

You will be reading this section after you have downloaded the StarTraX installer from the gpsAnimator web site and installed it on your computer. You will now have a StarTraX icon on your Desk Top and a StarTraX entry in your Start/Programs list, either of which will start the StarTraX program.

Since StarTraX interacts directly with the Google Earth web site, you will need to be connected to the Internet for it to run.

Starting StarTraX

Once installed, you can find StarTraX in your familiar Start/Programs folder:

Once StarTraX is started Google Earth displays its spinning icon while it is loading, and Loading Google Earth. Please wait.... is displayed in the "Track Details" text box.

Once Google Earth is loaded the message Now 'GO TO' a track file is displayed.


If you don't already have Google Earth installed on your computer , you will get this invitation to download and install it


If the icon doesn't get replaced with the next screen after a few moments, then it indicates that you have a problem connecting with Google Earth.

Check your internet connections and start again

Assistance When you place and hold ("hover") the cursor on any button or other control, a message ("tool tip") will appear with further information. For the main form, the tool tip is For operating instructions, go to

International Assistance StarTraX initially deduces your language preference from the way you have configured your International Settings in Windows.

You can also Select your language from this drop-down list.

You can contribute to the translation of StarTraX by following the Translate tab above.

Once Google Earth is loaded, you will be presented with this opening screen.

In the top left corner there is an image of a GPS receiver with a number of buttons that you can operate with your mouse.

The right hand section contains the Google Earth screen with its navigation control in the top right corner.


You can minimize or maximize the window or close the session with the familiar Windows form controls.

Control buttons - before a track file is loaded

The buttons that are active appear bold, inactive buttons are "greyed out"

 Select a track file to replay...The Go To button allows you to select a track file that you have saved previously to your computer. It opens the familiar Windows dialog box displaying file typesthat it can process.



  Exit StarTraX.The Quit button ends your StarTraX session.

  Registration Key entry form... The Registration button is displayed until you complete the licensing of StarTraX, it takes you to the StarTraX registration screen.

  Open the main settings menu from where you can customize your replay options... The Menu button takes you to the extensive menu of options for controlling your replay experience

After selection of your track file

Once you have selected a track file, StarTraX loads the file and sends Google Earth to the location.

For the few moments that Google Earth requires to download the imagery of the area of your track it displays  Imagery loading progress...

Once the track is loaded, it displays  Track(s) Loaded.

Start and Pause the replay

You can press the Start/Pause button to Start or pause the replay. StarTraX starts to interact with Google Earth and begins the animation.

The Start/Pause button now displays , and, when pressed, will pause the replay, allowing you to explore the Google Earth image with the Navigation Tool which is not available while the animation is running.

By default it starts the replay at the first point in your track file.

Track Progress Indicator

Track progress indicator. Move the pointer to where you want the replay to re-start. You can "drag" the pointer to re-start the replay at a new time. As the replay progresses, the pointer moves along the bar and the local time of the current replay is displayed under the pointer.


Fast forward display speed

You can Control the replay speed. Increase the replay speed (256 is the maximum). with and Reduce the replay speed (minimum is 1 - normal speed). with .

Each click doubles or halves the previous value. A minimum of 1 and maximum of 256.

The higher the replay speed, the faster the images have to be displayed. This will inevitably result in some loss of clarity.

You can also start the replay at any point by clicking on a point on the track.


When your track is loaded, it is displayed in Google Earth as a series of lines joining your GPS track points. A numbered placemark is displayed every ten track points.

You can use the Google Earth navigation tool to "zoom in" to see your track displayed in three dimensions in Google Earth.

This allows you to navigate through the Google Earth.

You don't need to use the control if you have a mouse with a mouse-wheel experiment with the navigation it gives you.


Your track is displayed as a series of dots joined by colored lines

The dots are numbered and represent every tenth point recorded in your track file. The numbers are used to allow you to select a start position for the replay as described later.


You can right-mouse-click on a dot to display the details about that point.



The line coloring indicates the speed that you were going at the time.

The colors are explained in the Color Codes box which can be displayed by hovering the cursor over the Colour legend box below. Under the heading Colour Codes the speeds of Up to and Over are displayed in color.


It now generates a model appropriate to the theme it identifies from your track in Google Earth representing the position of a "Target Point" which moves along the track in real time.

Your viewing point moves with the model, giving you the effect that you are moving through Google Earth's world as if you were attached to the model.

At the end of your track the replay will stop. If you try to re-start at the end, it will alert you with End of track - re-select a start point.

Controlling the replay

Now that you are up and running, this section describes in detail all the buttons and controls that allow you to manage your track replay.

The Menu

Before getting into the details, we will briefly describe the Menu button which is the gateway to most of the controls and opens up a set of displays and options that we describe in the following sections


It opens an input form with three tabbed pages: Settings described below, Models is described later in the document and Scenery, is also described later in the document


If there is an animation in progress when the Menu button is pressed, the animation is paused until the Close button is pressed.

A number of the operations from the Menu option require the tracks to be re-drawn in Google Earth, during which time the Close button will be disabled and will not operate until the track has been re-drawn.





The settings tab provides access to a bunch of check boxes, buttons and data entry fields whose descriptions you can access by clicking on the links below.

Time Zone


View Mode

Start Point

Disp Dists.


Show Compass?

Hide track when running.

Time Slider

Smooth Track

Smoke trail length

Colour the track by:

Display Details


Cockpit Instruments

Show Clouds

IGC Altitude source

Track Selection

The first step in the animation process is to get StarTraX to read your track log file. The Go To button allows you to select a track file that you have saved previously to your computer. It opens the familiar Windows Explorer dialog box displaying all files with extensions that it can handle. These are: "gpx", ".igc", "nmea" and "plt".

You can also open a track log file in StarTraX using the Windows "Open With" feature.

You can also open multiple track files simultaneously using the "Multi track" feature.

Once the track file is selected, StarTraX reads the file and subjects the data to some serious analysis before displaying the track in the Google Earth window as a multi-colored line with a series of numbered points along its length.

Select start point

By default, once you have loaded a track the Start Button will start the replay at the first point in your track file.

You can choose to start at any point by clicking on a point on the track.

StarTraX then displays this confirmation box, showing the Selected point and asking Start animation from here.

Selecting a track and start point when multi-tracking

When you have more than one track loaded, you may wish to be a bit more particular about which point of which track you want to start the animation.

So, when you choose to start the animation, either from the start button or clicking on a point, we show the Multi-track start point selector dialog box with the selected Track and start Point selected.

From here, if you click on the expand button of the drop-down Track box, it will display all the available tracks, listing the track code from the display and the track file name. The currently selected track will be highlighted.

If you select a new track by clicking on an un-selected track, then the points for the newly selected track will be displayed. This will allow you to review the available tracks and points and select the point on the track at which you want to start the animation.

The Cancel button will cancel any selection made.

Synchronize the tracks

The Compare tracks facility allows you to Synchronize the tracks to compare similar tracks from different times.

Click the button to Synchronize the other track(s) to pass nearest this point at the same time. It looks through each of the other tracks for its point nearest to the selected point. It then applies a time offset value (displayed) to the track to cause the new track to re-start at this point. This facility may be useful if you want to compare multiple performances around the same course.

When the tracks are synchronised, the button will allow you to un-synchronize the tracks and return the track data to the original condition.

Control the view position with mouse or buttons

When describing the viewing position we refer to a camera which is effectively recording the 3 dimensional (3D) world and presenting it on your computer screen in 2 dimensions (2D). So, whenever you see a Google Earth scene, it can be thought of as having been taken by a camera positioned at a certain location (latitude and longitude), at a certain altitude, facing in a certain direction (North, East, etc), with a tilt in a number of degrees above or below the horizontal, and with a roll angle, where the camera is rotated along its centre axis.

You can control the location (latitude, longitude, altitude) and orientation (heading and tilt, but not roll) of the camera in StarTraX with either the buttons or the mouse. In all cases, when the animation is running, StarTraX will endeavour to keep the target point in the centre of the screen. In practice, this is not always completely achieved due to the competing pressures of calculations.


There are three sets of buttonsallow  which you to control the position of the camera:

Range: the distance of the camera from the target point. You can Move closer to the target point. with and Move away from the target point. with The initial value is set at 50 metres. Each successive press of the button moves the camera in or out by about 30% of the current value.

Heading: Allows you to look around to the left or right as the animation progresses. Move your view in the direction to the left. with and Move your view in the direction to the right. with Each click of the button increases or decreases the angle by 15 degrees per click

Tilt: The up/down buttons control your viewing angle in the vertical plane above the current track segment. Look up to the target point. with and Look down on the target point. with .

It defaults to 15 degrees above the track segment and can be changed in the range of 0 degrees, along the track to 90 degrees, straight down and -90 straight up.



Control the Camera with the Mouse

In addition to the camera control buttons described above, you can also control the camera with the mouse using gestures similar to those provided in Google Earth. They rely on you having a mouse equipped with a mouse wheel configured in the standard Windows fashion.

The camera mouse controls will only work if your cursor is over the lower section of the left hand panel i.e away from the Google Earth part of the screen and any of the button controls GPS image in the top left section. They are only active with the mouse cursor positioned in the lower left, grey section of the screen.

The cursor is displayed as a "crosshair"

while you are using the mouse to control the pan and tilt of the camera.



Pan left and right

With the mouse wheel pressed, move the mouse left and right.

Tilt down and up

With the mouse wheel pressed, move the mouse forward and back.

Zoom in and out

Roll the mouse wheel forward and back to zoom in and out.

Four view modes

The four view modes allow you to Control the way the camera follows the target point.


Position above and behind the target point. Stay in line with the direction of travel. In this case, the observation position and orientation remains in line with the direction of travel.


Follow the target point but fix the direction of viewing.

The "Observing" mode was specifically designed to follow a glider or paraglider's track, which tends to follow a circular track as the pilot strives to stay in the thermal.


Lock the camera on to the target point so you see the the target point's view. You can still change the camera's orientation, swinging the view left and right, up and down with either the mouse or the buttons, but you can't move in and out the camera position remains fixed relative to the target point


In this mode, the camera does not follow the target at all. You must use Google's navigation controls to follow the track. This option is not recommended for normal use.

You can modify the dissipation behaviour of the smoke trail with the Smoke Trail length buttons

Short : The "smoke trail" fades after 1/2 minute.

Med. : The "smoke trail" fades after five minutes.

Long : The "smoke trail" does not fade.


When StarTraX loads a track file, it makes a model selection based on the theme it deduces from your track. These models have been selected from Google Earth's huge "warehouse" of models that enthusiastic virtual model builders have been constructing and providing for our enjoyment. It's at if you want to check it out.


The Models menu enables you to make your own model selection from the Menu -> Models option.

This list is populated from our web site ( when you start your StarTraX session, so we will add to it as we find new and more amusing models to play with.

The first line gives you the instructions you can choose a new model by following the instruction : Model Selector: Double-click on model or 'any key' to exit.. To exit the screen, press any key when the cursor is in the frame, and no change will take place.

When the model has been selected, its name appears in the Selected model: window.

You can expand or contract the sections by clicking on the + and symbols it's all very intuitive.

You can play to your heart's content with these models they are downloaded from our web site as you select them, and you can play with them as you like. You can put the 747 on a ski-field or go flying with the yacht!


We are deeply indebted to all the enthusiastic model builders for this rich resource of models.

Here are some of my favourites:

The ME109

the Audi Le Mans

The 747


Include your model

If you build or find a model that you would like included, send us an email containing link to the model and we'll consider it for inclusion. We have to do a bit of work on most models before they can be included.

If you are building or manipulating models for inclusion in StarTraX then the following tips will make our job a little easier:

Model type: Google Sketchup (.skp)

Orientation: have it facing towards the green axis, so that in its normal position it is going away from you.


a)      positioned with vertical axis through the viewer's position with vehicles, this is the position of the driver's head.

b)       Positioned with the base of the model (wheels) on the ground

Scale: realistic. Some models are scaled very small or very large

We calculate, store and use a value of the height of the pilot's eye above the ground for each model

Multiple file formats

The major enhancement in 3.6 is a change in the method of handling track file formats. Initially (because that's where we came from) we only handled the .plt file format from OziExplorer .plt. later enhancements introduced gpx, nmea and kml formats. Now that we have realized just how many formats there are "out there" we have taken the following approach.

The "native" file format that StarTraX handles is gpx version 1.1.

GPX is an open standard for recording GPS data. There are a number of free applications that will read data from a range of GPS devices and save them to the GPX format, with a .gpx file name extension, including GpsBabel and EasyGPX.

There are two GPX formats 1.0 and 1.1. GPX 1.1 was released in 2004 and is the only version that StarTraX will accept.

To handle other formats we have incorporated GpsBabel into StarTraX to convert files to the gpx format. This happens "in the background" you will see GpsBabel briefly flashing on the screen when you ask for a non-gpx file to be loaded.

We use GpsBabel to convert your non-gpx files to gpx and save the new gpx file in your %TEMP% (by default C:\Documents and Settings\{user}\Local Settings\Temp) directory before loading them into StarTraX.

Currently we handle the following formats through GpsBabel:



File extension


GPX XML version 1.1


StarTraX natively

FAI/IGC Flight Recorder Data Format


GpsBabel -> StarTraX

NMEA 0183 sentences


GpsBabel -> StarTraX



GpsBabel -> StarTraX


In this version we have added the FAI/IGC Flight Recorder Data Format .igc format to the list of available formats. Over time, as users request more formats, we will incorporate them into StarTraX.

Meanwhile, if you have a format that is not in the above list, you can use GpsBabel to convert them to gpx version 1.1 and StarTraX will happily process them.


For those of you who engage in your activity with GPS-equipped friends or competitors, you can now replay all your tracks together in StarTraX.

To access this feature, you first place the track files that you wish to simultaneously replay in a single Windows Folder. You then click on the Multi-track check box in the Settings tab of the Menu option. This will Enable multiple tracks to be displayed together.

When checked, the file selection dialog box, opened from the GO TO button, allows you to select multiple track files with familiar Windows mouse gestures:

To select files individually, use Control + Click (hold down the control key and use the mouse to click on the files you want to open).

To select a range of files, use Shift + Click and select multiple adjacent file names from the display.

When you click the Open button, StarTraX reads the files one by one and presents them in the Google Earth window.

You might have to be a bit patient here as there's heaps of work going on in the background to calculate the position of the points and display them in Google Earth.

The tracks are separately colored and are labelled A, B, C etc.


The feature has been developed primarily for paragliders, and will load a different colored paraglider for each track.

Not that it's likely to bother you, but there's a limit of 26 on the number of files that can be opened concurrently.

Multiple tracks in a file

Some GPS software generates gpx files containing multiple, separately named tracks.

When you load one of these files into StarTraX, it detects the presence of multiple tracks and presents you with this StarTraX Track Selector. File (your file name) window. Your track file contains a number of individual tracks. Select a track from the list below. with the instructions: Select a track from the drop-down list.

The track file name is displayed ("Ethopia" is the file name in the example) along with the name of each track in the file.

You can select a single track, or if you select the "All" option, all of the files together.

Track smoothing

Apply smoothing to your track to turn sharp turns into curves. GPS track data consists of a set of points recorded in your GPS at its own time intervals. GPS tracking is also only accurate to a few metres, so if you can record at high speed, you get high-speed zigzags, and if you record at low speed, you get further spaced zigzags.

What we have done is to take your points, at not less than 3 seconds intervals, and we have generated nine new points between each of yours, to form the sweet curve that you see below. The new points are just as "honest" as the original points as the new track still passes exactly through each of your recorded points. We have just eliminated the sharp corners.

Turns this plotted hang glider data

into this smoothed track


Or this ski track


Into this:


StarTraX uses an algorithm to deduce a 3rd order polynomial for a line between the second and third points in every 4 point sequence in the track, using the first and third segment to provide a starting and ending gradient.

It then generate nine new points along that line and add them to your track (with appropriate time stamps and altitudes).

But this is all done between loading the file and starting the replay, so it doesn't impinge on performance at all.

It took me a long time to find an appropriate approach to the smoothing task. Much of the material published on the web relates to "splines", which did not suit my needs as I was determined that the smoothed track would be as "honest" as the original track and would therefore have to pass through all the original points. The spline solutions provide a nicely smoothed track, but they do not religiously go through the all the original points.

I am indebted to a sailing mate who, as a nautical engineer, had an old textbook on computer methods for ship surface design. It contained the following page describing and detailing a Fortran subroutine it must have been 30 years old!

I still don't really understand the method but I converted to Visual Basic and implemented in StarTraX and after extensive testing, I'm satisfied that it does a good job. Thanks Malcolm.

Units of measure for distance and speed

Choose your preferred speed and distance units.

Different nationalities and different activities call for different units of measure of distance: kilometres, statute miles, nautical miles, feet and metres. These different distance units influence the derived values for speed: kilometres per hour, metres per second, miles per hour, feet per minute, knots.


The Units "drop-down combo box" allows you to select the units in which speeds and distances are displayed











Google Earth


km. and metres




metres/ kilometres


nm. and feet






m. and feet






This setting also changes the units Google earth uses when displaying altitude and distance when StarTraX is Paused. The screen shot below shows an example of the display when Metric units are selected.

And again, when Nautical is selected:

Time zone deduction and manual override

StarTraX deduces your time zone from your longitude, change the time zone in hours +/- UTC. It assumes that the time stamps in your track file have been recorded in UTC (GMT).

It deduces the local time zone from the longitude of the track (actually just the first point) and displays the GPS time (File:) and local time (Local: ) in the point display and the display window. It calculates the time zone by working out in which 15 degree segment of longitude the point lies, and adds or subtracts one hour for each segment. (360 degrees / 15 = 24 hours)

It makes no allowance for Daylight Saving time or for local time zone variances. You may override the calculated time zone by entering a new value in the Zone entry field box.

If you are playing a track that was recorded in a different time zone than your PC is currently in, then GE will calculate the local time based on your current location, not the track's location.

Un-timed tracks

If StarTraX detects that the loaded track file contains no timestamps, it will offer you this option: Un-timed track - what speed would you like? which gives you option to replay the track at a speed of your choice in your currently selected speed units.

Type in a positive number.

Google Earth layers street, buildings, borders

The check boxes in the Menu->Scenery form allow you to turn off (or on) the three native layers in Google Earth. By default all three are turned off.

The only reason you might want to change these settings would be if your view was too cluttered, or if the loading of the layers slowed down the performance.


Roads Layer Show the position of roads.

Borders Layer Show 3D buildings.

Buildings Layer

I'm particularly impressed with the ski terminals and lift towers displayed at Whistler:




In the Scenery kml files section you can either import some scenery files that we have assembled from various sources or you can load your own from the Menu ->Scenery form:

We acknowledge the unauthorized use of some excellent scenery files that we located on the web site in this feature.


Included scenery

These are scenery files we have found on the internet or generated ourselves. If you have any files (kmz, kml) you would like incorporated, email the file(s) or their URL to us (at [email protected]) and we'll include them. The files are downloaded by StarTraX from our web site at run-time, so no software update is required to deploy an update. We have assembled a small (but hopefully growing) selection of scenery that you might enjoy. If you navigate (via the GE side of StarTraX) to their areas, you will see them displayed. They are mainly ski-runs and lifts.


Local files

You can also loadSelect a kml file from your local disk drive to display in StarTraX. by selecting the Local button and navigating to your file.

At this stage we only handle kml files, not kmz.


You can Show or hide the scenery layer from the Show Scenery Layer check box:

Tracks in Scenery files

If your file contains KML "lineString" features, they will be available as tracks in the track selector opened by the GoTo button.

For this type of track to be available in StarTraX, the linesString feature in the kml file must have a value in the <name> attribute. This is not a requirement of kml, so if your file contains lineString features without a name, they will not be playable in StarTraX.


They mostly contain tracks of one sort or another, that you can also follow at your own speed from the GoTo button.

This list shows all the named lineString features in your scenery kml file, sorted in alphabetical order.


As the kml feature contains no time stamps for StarTraX to use to calculate speed it announces Un-timed track - what speed would you like? Units: , you can supply your own speed to follow those tracks. It defaults to a value of 20.


Surface(Aerial)? override

You will only need to use this control in the unusual circumstance that your track encompasses both aerial and surface components, or if StarTraX is unable to determine the nature of your track and you wish to Switch the track style between being "in the air" and "on the ground". . I have a track that includes the flight to the ski fields (aerial) and the day skiing (surface). StarTraX struggles to determine whether you want to view the aerial or surface component of the track. This check box allows you to override StarTraX's determination and display the track on the surface or using the altitude recorded by your GPS (aerial).

Making the replay realistic

This section describes features over which you have no direct control which make StarTraX a realistic replay experience.

Google Earth interface

StarTraX relies entirely on the truly amazing Google Earth to display your moving track in 3D space. In mid 2008 they released a new and powerful method (the Google Earth API "GEAPI") for programmers (like me) to interact directly with the GE globe and have regularly released enhancements and improvements to the interface. And of course they continue to release more and more detailed imagery on a regular basis.

This has provided an amazing 3-Dimensional space for developers like me to play in. We don't have to worry about so many of the complexities of working in a 3D space maps, land form, ground texture, scale and projection of a 3D world on a 2D computer screen. This is all handled by GE, all we have to do is to tell GE to put our model aircraft at a certain location (latitude, longitude, altitude) and show it as if from a camera positioned at a certain location, pointed at the model. The underlying language used for sending these instructions to GE is called KML whilst the interface to the KML is via the Google Earth API

So, what you see in the right hand pane of StarTraX is entirely courtesy of Google Earth: the landscapes created from satellite photography draped over an underlying structure of ground contours, with layers of streets, borders, town names and 3D buildings with your 3D avatar appropriately located, scaled and oriented in the landscape.

Progresses in real time you see your trip as it happened

At run-time, your position and the camera position are re-calculated around 60 times a second based on your previous position and your current speed and direction. GE is then instructed to move the target model and the camera to the new point. GE then has to re-draw the scene based on these new positions.

Smooth camera pan and tilt

Because the GPS track is a series of points, the track you see is a series of straight lines linking the points. This means that after the camera has followed the target along one segment, it has to re-position abruptly to follow it along the next segment. With small direction changes this wasn't a problem, but with large ones especially when the track is a glider orbiting in a thermal, the abrupt camera position changes led to some very abrupt changes of view.

In earlier versions we were relying on GE to provide a smooth transition from one camera position to the next, but this was not always effective, so we now control these camera transitions by anticipating the next segment turn and tilt angle and start to move the camera into the next position at the start of the segment, so that once the target has reached the start of the next segment, the camera has been swung into position for this next segment.

we link the camera panning with thermalling (gliding in climbing orbits). When thermalling, the camera pans continuously, at a rate determined by the turn angle. When not thermalling, the camera pans at a fixed speed, starting later in the segment, just in time to get the orientation correct at the end of the segment.

Realistic banking

Whilst generating the smooth track above, we can also work out the G-force that would have been generated in the turn and have visually represented it by banking the model appropriately. So now when the paraglider turns into the thermal, or the skier carves into a tight turn, you can see the model doing exactly the same thing.

The above shots were taken whilst in Observe mode. When in Follow mode, the camera also banks, providing a realistic replay. We have drawn in the horizon in the shot below to emphasise the point.


We have extended this banking to all tracks, not just those modified with the track smoothing feature.

Track Theme derived from track data

StarTraX analyses your track to interpret your activity. It determines which of the following themes that the track most closely matches. I'm not giving too much away about this process except to say that it analyses the points in the track for speed, altitude, and vertical speed and categorizes the track into one of the following categories which I have called Theme.

Whilst this works in general, it can get confused when the characteristics are not consistent throughout the track. For example, I have a track of a journey from Sydney to a ski resort in Japan, which includes two flights, a train and bus trip and an afternoon skiing. StarTraX deduced Acft-Light.





surface, walking speed


surface, faster than cycling


surface, very flat, pretty slow


surface, not so flat cycling speed


aerial, slow


aerial, fast


aerial medium speed


Acft-Light and orbiting track


surface, lots of vertical motion

It re-assesses the theme each time you load a new track. The theme it deduces is displayed in the in the file display:

Once it determines the Theme of your track it displays an appropriate model to represent your activity, like a skier, car, boat etc.

Ground altitude

If it can deduce the ground altitudes then it uses the ground altitude rather than the GPS altitude when following Surface (as opposed to Aerial) tracks. This provides a more realistic replay as the altitude that the GPS device records can often be 10's of metres above or below the ground surface that Google Earth uses in the display. Using the GPS reported altitude in these cases would cause the track to be displayed above or below the Google Earth surface.

You may wonder why we go to this effort, as GE allows lines and points to be drawn "clamped to the ground" . Well, the answer is that we do it to improve the way the camera works. By retrieving the ground altitude at both ends of each segment, we can calculate the actual tilt of the track, and position the camera accordingly. This may not seem a big issue, but it was a problem when following a skiing track down the mountain. With no actual ground altitude, we couldn't get the excitement of pointing the camera down to follow the track down a steep section.

Smooth replay tricks

A significant proportion, probably 30%-40%, of the development effort has been spent on getting a smooth replay eliminating the jerkiness from the target point movement and moving the camera smoothly.

As you probably know, movement that you see on the screen of your TV, cinema screen or computer is not actual movement at all but the display of slightly changing images in rapid succession. The frequency with which the images are displayed is called the "frame rate", usually measured in frames per second (fps). The minimum frame rate required for the human eye to perceive smooth motion is influenced by brightness, image blurring etc and is the subject of extensive study. Cinemas work at 24 fps but use image blurring to enhance the effect. TV's work at higher rates.

The challenge we faced was to complete all the calculations required to generate the next frame and have them displayed in Google Earth within the allotted time frame. After much blood, sweat and tears, we have managed to streamline the code sufficiently to achieve a frame rate of around 50 fps when running on a basic PC with a standard video card.

StarTraX doesn't run in isolation on your computer the Windows operating system is managing the computer and is allocating computer resources CPU cycles, and memory, to all the processes running on your box according to that process's priority. StarTraX runs at the highest possible priority and we assign the lowest priority to the Google Earth component, which runs as a separate process. This means that occasionally the background scenery in GE is a bit slow to refresh, but we chose that as an acceptable compromise in the search for a smooth replay.

Up to a point, you'll get a smoother replay on a more powerful computer or a higher quality video adapter. On the other hand, running on a slower computer, or one that is burdened with other tasks, like an office server or a Mac running Windows or VM, may result in degraded performance.

Track Information

This section describes features that provide you with information about your track.

Animated track overview

Whilst your track is being analysed and being loaded into Google Earth, your track is displayed on the GPS's screen.

Inevitably the display is small, but it does give you an overview of the track.

The screen has been scaled to hold the entire track, and a small scale bar is shown on the lower left (highlighted with a red circled) to indicate the scale, and to confirm the orientation, North is always at the top.



Once your replay commences, your position is indicated by a small red box which follows your track throughout the replay.


If you are replaying multiple tracks, then your selected track and position are displayed as above, but in addition, the position of the other target points, with their file name, are displayed as a small yellow point. In the example, we're following "My Track" and we can see Terry's location around 1 km to the north.

This can be useful when locating your friend's position.


When the tracks are extensive and the separation of the target points is small, the details do tend to merge and become a bit difficult to distinguish.




Numbered points

StarTraX generates a series of numbered dot points along your track in Google Earth. The primary purpose of these points is to allow you to select a point on the track at which to start your replay. You can also right-click on these points to find out details about the track at that point.

The points are numbered from zero (the first point) and occur every ten points along your track. We discovered that putting a point at every point of your track generated a very cluttered display.

This explains that the point number displayed with the point (16 in the example) refers to point number 160 in your track.

When you select track smoothing, because we now have an additional nine points for every original point on the track, the points are drawn at every 100 points on the new track.


When multi-tracking, the points are labelled A, B, C.. to Z (that's why there's a maximum of 26 tracks) and each point is painted in a different color to assist you to identify them.


Track Profile

This graphical analysis tool, which Display your track as a graph of speed, altitude etc. by time or distance... allows you to do some serious evaluation of your performance. It is launched from the button.

The initial view shows a graph of altitude against time. The blue line follows your track, the brown line follows the terrain.

You can change the values displayed on the Y Axis to Altitude, Speed or VSIby clicking on the buttons.

The X Axis can display either Time or Distance depending on your choice of button.


The Zoom buttons works a little like a camera zoom lens, increasing the magnification of the view to allow you to Zoom closer or Zoom more distant to examine your track in more detail.

Mouse gestures You can also use the mouse scroll wheel to zoom in and out.

The zoom-out is limited to displaying the entire track. The zoom- in works as long as there are at least three points in view.

The Pan buttons are most effective on conjunction with the Zoom button to Move the view left or Move the view right .

Mouse gestures You can also use the mouse to pan by holding (any) button and moving the mouse left or right. The cursor changes to the familiar "hand" symbol while this is operating.


The graph uses the distance units selected for the track and displays the values on the Y-axis grid-lines

To assist you to relate the graph to your track in Google Earth, In addition to the time or distance, the X-axis shows the display point number (Pt.)nearest to that grid line

StarTraX will continue to replay your track while the profiling screen is displayed in a separate window.

Flight instruments

The Cockpit Instruments check box causes StarTraX to Display all the flight instruments. when the track is playing.

Speed Indicator

The speed indicator displays your current speed in the units you have selected:

The dial is calibrated from the current track, with the green sector representing the mean or average speed of the track, with the speeds slower than average on the left ranging from magenta to blue and the speeds faster than average on the right, ranging from yellow through red.

It uses the same color coding that is displayed in the speed legend for that track.


Viewing Direction

The viewing direction is indicated by the position of the rotating compass ring relative to the fixed marker.

This example indicates you are looking slightly east of North at a compass bearing of approx 20 degrees.

The compass ring rotates as you change your viewing direction.

Track Direction

The track direction is indicated by the position of the nose of the rotating aircraft symbol.

In this example the current track is about 235 degrees.

In StarTraX, all compass headings are calculated from the track positions' latitude and longitude and so are relative to true North, not magnetic North.

The track direction indicator rotates according to your track direction.


The altimeter is based on one used in a light aircraft and is calibrated in feet.

It shows hundreds of feet by the position of the "big hand", thousands of feet by the "little hand" and tens of thousands of feet by the white line.

This example is showing an altitude of 18,950 feet.


The variometer shows the vertical speed in hundreds of feet per minute.

It's based on one in a light aircraft.

The example shows us descending at 300 feet per minute.

Metric instruments

When Metric units are selected, the altimeter and variometer display metric units.

Smoke trail

The "smoke trail" is the track left behind the target point. As your model moves along its track it generates a thick line behind it, much like the smoke trail generated by formation aircraft in a fly-by. Thus the name "smoke trail". The trail is colored according to the currently selected track coloring. By default, each section of the smoke trail becomes progressively fainter until it disappears (dissipates) after five minutes. You can modify the dissipation time by using the smoke trail length control.

The smoke trails will be erased and re-started when you re-start the display at a new point, change the track coloring selection or change the distance units.

You may notice that the smoke trail is not generated immediately behind you (the model) but only when you reach the next point on the track. For performance reasons, the smoke does not appear immediately behind the model, because refreshing the smoke trail that frequently just puts too much load on the drawing engine and impacts on the smoothness of the replay. So the smoke is generated for the track behind you when you reach the next point.


Track color

The line coloring indicates the speed that you were going at the time. The colors are explained in the Color Codes box which can be displayed by putting the cursor over the "Color Legend" box pictured right.

The colors graduate from slow, in blue to fast in dark red.

StarTraX uses statistical methods to determine the categories based on the speeds it finds in your track file.

These categories will be different for each track file and the speeds are displayed in your choice of units which you can choose as described below.



Display Details

From this menu option you can Select which details to display next to the target point. as the model moves along the track. Here I am with speed selected, skiing at 49 kph.


Don't display anything.

File Name

Display the track's file name next to the target point.


Display your speed next to the target point.


Display your vertical speed (VSI) next to the target point.


Display the distance from the start next to the target point.


Display your altitude next to the target point.

Having them display next to the model required too much processing power causing display problems, so we went for a happy compromise and had them appear at the start of each segment.

The units are as selected in the units drop-down selection kph, mph, knots etc.

Hide track when running.

Some users like to Control if the track remains displayed while the replay is running., some don't. This provides the flexibility of choice.

This shows the track hidden

Here, the track is not hidden:

Start Point

The Start Point "text box", Display only - shows where the replay will start next. displays the point at which StarTraX will commence (or resume) playing the track. It is a display-only field to provide some feed-back of where the replay has got to. It does not allow you to enter any data, it's just a display.


Point information display

You can right-mouse-click on a dot to display the details about that point.

The date(local) has been calculated from the timestamp on your track file which is recorded in UTC (old GMT) and converted to a local time based on a rough calculation of your time zone according to the longitude of the first point on the track. If the calculated time zone is incorrect, you can change it here.

The Altitude is reported in your currently selected Units and the latitude and longitude are displayed


Track Details displays

You can discover detailed analysis of your track by hovering your mouse over the File details or Point details panels.



File details

This display is populated once you have selected a track file and it has been analysed by StarTraX.

The name of the file you have loaded appears under the  File heading after we strip off the trailing file type (.gpx, .igc).

Track: is displayed when multi-tracking, and provides a reference to the point letters on the GE screen.

Theme: is the Theme deduced from the track file.

Start time: is the time and date of the first point in the track

File time: using the File date (UTC)

Local time: the local time after applying the time zone.

Duration: the elapsed time of the track in days, hours and minutes

Distance: The total distance covered in the track. This is calculated by summing the individual distance between each pair of points. The distance of an orbiting gliding track will include the distance in the orbiting.

Mode: Aerial or Surface. StarTraX analyses your track and deduces if the activity you were engaged in was Aerial (flying, gliding, paragliding etc) or Surface(driving, skiing, sailing etc), by comparing your GPS reported altitude with the ground altitude and determining if more than 20% of the points were more than 500 metres above ground.

When in Aerial mode, it displays the track at the altitudes recorded by the GPS; when in Surface mode, it displays the track on the ground irrespective of the altitude recorded by the GPS.

Point details

This section reports information regarding the current segment of the track. In this context, the segment is the short path between the previous and the next point recorded by your GPS. These points may be only seconds apart, but in each segment StarTraX calculates, uses and display the following information:

Point: The point number of the first point of the current segment.

Date(local): The date and time in the local time zone.

Altitude: The altitude of the point. If it is a surface track, then this will be the ground altitude at the point.

Location: reported in degrees, minutes and 2 decimals of a minute.

TILT: The angle of the segment from the horizontal in degrees above the horizontal.

HEADING: is the direction of travel in degrees true (not magnetic)

WIND: If this is an orbiting glider track, the currently detected wind speed and direction.

SPEED: Your actual speed along this segment reported in your chosen units of measurement

VSI: Vertical speed. It is useful when animating flight data glider pilots and paragliders should enjoy this. When in Aerial mode, it is calculated from the GPS altitude, otherwise it's calculated from Google Earth's altitude.

This is an option with limited application but has been included as a user option. Select to Turn on Google Earth's "Time slider" control.

This is a useful facility if you want to visualize part of a track that goes through the same area a number of times - for example performing laps around a track, or travelling through the same area over a couple of days.

When it initially opens, the beginning and end "handles" are closed at the start of the replay:

To reveal the portion of the track you're interested in, you have to "grab" the "handles" with your mouse and move them to cover the time period of the track that you're interested in:

When you check the time slider, your track is re-drawn in Google Earth with each point's time stamp attached to the points.

Disp Dists.

The "check box" defaults to un-checked. When checked, it will Display the distance from the start next to the track point.

When you check this option, the distance from the start of the track is displayed on the track at every tenth track point along with the track point number.

When you change this setting after you have loaded a track, StarTraX takes a few seconds to re-draw the track using the setting.



Gliding features

StarTraX has been adopted by a significant number of enthusiasts of un-powered flight hang-gliding, paragliding and gliding and they have triggered the development of a number of features specific to their sport.

Colour the track by: VSI

The allows you to Control the colouring of the track lines. You can Colour the track by speed. (default) or Colour the track by VSI.


When the VSI option is selected, the color legend reports VSI in the appropriate units


Clouds over thermals

Clouds can be generated above orbiting glider tracks. As a visual clue to the size and location of thermals, we've positioned a white, semi-transparent cloud at the top of each thermal, whose height is proportional to the strength of the thermal.


In this screen shot below, you can see a towering Cu in the foreground, indicating a significant height gain (in this case nearly 4,000 ft), and some smaller ones in the distance.


It's semi-transparent so as to not be too intrusive. The thermal strength is measured simply as the value of the height gained in the thermal (not the rate of climb, which could be a thought for the future).

They are only generated for gliding, paragliding or hang-gliding tracks.

You can toggle the visibility of the clouds from the Show Clouds check box on the Settings Menu.

This check box is displayed when StarTraX detects that your track is a thermalling gliding track, i.e. an aerial track with lots of orbiting. In this case a Cumulus cloud is generated at the top of each detected thermal.

The strength of the thermal is reflected in height of the cloud.

This check box allows you to toggle the visibility on or off.

Wind speed and direction when gliding

This feature only works for glider, paraglider and hang-glider tracks as it depends on orbiting tracks to determine the wind speed and direction.

It analyses the way your GPS speed varies as your heading changes through a series of orbiting turns. If you maintain a constant airspeed, then, when you head upwind your GPS speed will be lower than when you head downwind.

This can be seen from a typical thermalling track:


Here we have a portion of the track of a glider orbiting in a thermal. (The start point is at the top). With the speed indicated by the track coloring as shown it's pretty obvious that there is a wind from the north - fast towards the south, slow towards north.

StarTraX looks for portions of the track that display orbiting behaviour and uses the variation in the track's speed as it changes direction to mathematically deduce the wind speed and direction.

It makes the fundamental assumption that you have maintained a constant airspeed during the manoeuvre which of course is impossible in practice, but works pretty well on average.

The resulting speed and direction are displayed in the compass rose using colors and text to indicate the wind strength and a graphic to indicate the direction.

The graphic is a line drawing of Aeolus the wind god, blowing in the direction of the wind.

In this example the wind is from the North East, towards SW

The coloring indicates the wind speed, using a similar palette as for track speed, using the following colors and text to indicate the speed. We used the traditional Beaufort scale ( to classify the wind speeds, and made the assumption that no-one would be gliding in winds over force 5:




Bft force no.






< 1

< 1




1.1 5.5





5.6 11





12 19









5 and above

29 +

16 +


The actual values of wind speed and direction are displayed in the track display as shown. The wind direction is calculated to the nearest 1/16th of the compass or 22 1/2 degrees:

working clockwise from North, the compass points are abbreviated as follows:


The caption WIND S at 6 kph indicates the wind speed and direction deduced from the track details.

conf.: Low, Med or High indicates the confidence level of the reported value, and indicates the accuracy to which StarTraX has determined the wind speed.


The confidence level is affected by a number of factors, but mainly by the accuracy with which the pilot maintains a constant airspeed.

If it is uanble to deduce the wind, it displays Not available

To accommodate the reality of wind conditions at different altitude levels, we re-calculate the wind for every 1000 ft of vertical altitude. So, if you entered the thermal at, say, 5253 and exited at say, 8312 then we'll calculate the wind at the four levels: from 5253 up to 6253, 6253 up to 7253, 7253 up to 8253 and 8253 up to 8312.

IGC Altitude source

Control which altitude is used in IGC files with barometric and GPS altitudes. The IGC format, widely used by pilots of gliders, paragliders, hang gliders etc, allows for the altitude determined by the GPS ("GPS altitude") and the altitude recorded by the barometric altimeter ("pressure altitude") to be recorded against each point. These two readings are always different for a number of perfectly valid reasons that we won't go into here. As StarTraX started out to be a GPS track animation program and it can only display a track with one altitude, we originally took the decision to ignore the pressure altitude and to rely on the GPS altitude when animating these tracks.

However we have gone back to providing you with the option of loading either track once you have selected a file that contains both the pressure altitude track "PRESALTTRK" and GPS altitude track "GNSSALTTRK". (These names were dreamt up by other folks, so don't shoot the messenger.)

You can choose to suppress this display by choosing your preferred altitude source from the Settings menu.


If you're not loading IGC files, or if your IGC files only have one altitude, then this control has no effect on the way they're handled.

If they do have both sources, then you have three options:

Ask: Prompt for a decision at run-time. StarTraX will present you with the track selector every time you load a file with both types of altitude

it will prompt you with Please note: IGC files may contain both barometric altitude from the altimeter (PRESALTTRK) and GPS altitude (GNSSALTTRK). Set your preferences in Menu->Settings->IGC Alt source

GPS Alt.: Use the GPS altitude.

Baro Alt.: Use the barometric altitude.

Route and turn points (IGC files)

If your IGC file contains your route and turn points, then StarTraX will display them as additional "Scenery".

You can hide or display these by toggling the "Show Scenery Layer" check box in the Menu/Scenery form.



This feature has been developed from IGC gliding files downloaded from the OLC and bgaladder sites. Bearing in mind that StarTraX doesn't directly read IGC files, it relies on GpsBabel to convert them to GPX format, we have found that GpsBabel identifies this data and records it in the GPX rte (route) and "rtept" (route point) elements.

If you have GPX files with these elements then you should get the same result.


One of the annoying side-effects of this is that StarTraX interprets the route as an alternative track, so when you want to go to another track file, it first invites you to follow one of the legs of the route

Just click the Cancel button and you'll be taken to the familiar Windows Explorer file selection form.


Different models when loading multiple paragliding tracks

If you are multi-tracking paraglider tracks, StarTraX will assign a different model to each of the first five track from the list of paraglider models in the list. For more than five tracks, the 6th and subsequent track just get the default first model.

I know it's a bit biased towards paragliders, but it's just one of those quirky by-products of the development process.




This section describes features that are aimed at simplifying and streamlining your sessions in StarTraX.

"open with"

In Windows, you can associate an application or program with a file type, like Word for .doc, Excel for .xls, Notepad for .txt.

You can now make StarTraX the "Open With" program for your track files, and then if you applied this to your IGC and/or GPX files, then a double-click on the file the file in Windows Explorer will open the file in StarTraX.

If you use this technique to open a file whilst StarTraX is already playing a track, it halts the current track and opens the new track.

If you have "Multi-Track" selected, it will open the new track as an additional track, leaving the previous track(s) loaded, otherwise ("Multi-track" not selected) it will replace the existing track with the new track.

"Open with" is a Windows feature that is well documented here .

Settings retained

There is an almost bewildering array of buttons and check-boxes available to you to customize your track replay choices. Imaging having to re-select them each time you started StarTraX. To save you that inconvenience, we assume that you will normally like to retain your settings from one session to another, so the settings marked with an asterisk : will be retained from one session to the next. If you're interested, we store them in the Registry at :

Obviously we do not encourage you to make any changes here!

Version display and check

To retrieve version information from StarTraX, right-click on the GPS image:

It reports the versions of StarTraX and the Google Earth components: the Browser Plugin, GEPlugin and the development API, GeAPI.

Google Earth periodically updates its software which is automatically updated on your computer.

Every time StarTraX starts, it checks the web-site at to see if there is a newer version available. If there is, it generates the message: There is a new version of StarTraX available. Please download it from the web site at A new registration key is NOT required to run this version.

notifying you of your revision number and the revision number of the version available for download from the web site.


Tool tips

If you hover your mouse over any button or control in StarTraX, after about 1/2 a second a panel (called a Tool Tip) will open with some additional information about how to use the control.



Computer monitor size recognition

Different PC's have different monitor sizes with associated screen resolution. To provide as much detail as possible in the Google Earth frame, StarTraX adjusts the size of the Google Earth frame to fill the monitor.

So, on a standard 1024 x 768 monitor you get

On a monitor with 1280 x 1024 resolution you get the same sized left hand panel, but more space for the GE frame

Whilst at 1900 x 1600 you get even more space for Google Earth.

System requirements

StarTraX has been tested on XP and, as it's written in Microsoft VB 2005 .NET 2.0, is expected to run on Vista and Windows 7.

No versions for MAC or Unix, sorry, although there are users running it under Windows on a Mac. I suspect that the performance will be degraded as there is so much translation to get from Windows OS to the Mac's underlying OS.

It needs a minimum of 800 X 600 screen resolution (although it runs OK on a notebook with 640 x 480 resolution.)



Perhaps not a usability feature, but I had to put it somewhere!

Until registered, StarTraX displays a splash icon in Google Earth and will terminate after 4 minutes with Thank you for trying StarTrax. It will now exit. To register your copy please re-start StarTraX and complete the registration process from the Registration Menu. Check for Licensing procedures

To register StarTraX on your computer, you should go to the Registration Form of the web site and complete the Registration form.


We will then send you, by e-mail, a registration key which you enter by clicking the Register button in StarTraX.

This brings up the registration form in which you enter the registration key. Please enter your 8-character StarTraX Registration key in the box below.

The successful entry of a key results in the message: Registration Key successfully assigned. Please restart StarTraX to apply the code.

An incorrect key entry results in Invalid StarTraX Registration Key Check you have entered exactly eight upper case characters - no numbers. The StarTrax Registration key expires after five days.

The registration details are written to the registry on your computer and, because they are based on the MAC address of your network adapters (LAN, wireless network, Bluetooth, etc.) , they won't work on any other computer. If you change all your network adapter cards, which is unlikely, it will invalidate your registration. In that case please apply for a new registration key.


StarTraX is a project that has been developed independently from Google Earth, although it is totally dependent on the amazing functionality that is Google Earth.

We at have developed an application as a speculative project to display four dimensional (latitude, longitude, altitude and time) GPS tracks in on a 2-dimensional computer screen.

On the way, we visited

  •, who has a powerful tool to display GPS track files in Google Earth.
  • who have a neat tool in EasyGPX which downloads GPS data to GPX file format.
  • OziExplorer who have a great mapping program that interfaces with a range of GPS devices and creates .plt track files.
  • where we received useful advice on some of the trickier issues in developing in Microsoft's .NET environment
  • who have an excellent tool for manipulating GPS data, including unloading it from GPS units and converting between formats.

Bugs and Help

We have done our best to deliver a reliable product, but as with so many things, we are only human and are therefore fallible. Please report any errors, bugs or oversights with an email to [email protected]. Please be sure to include the version information and as much detail as you can.

You can also email us if you have any questions or suggestions for improvement to the program (or its documentation).

Program structure

We are occasionally asked about the development and structure of the program, so here is some information.

Development environment

The original development environment was Windows XP, Microsoft Visual Studio 2005 , .NET 2.0 and Visual Basic. In March 2011 we have upgraded our development environment as below.

Microsoft Windows 7

Visual Studio 2010

Visual Basic .NET 4.0.

The main impact to you will be in the installation or upgrade of StarTraX to version 3.9 or above will require the download and installation of Microsoft .NET 4.0. You will be guided through the download and installation of this upgrade and

Follow the prompts to download and install NET 4.0 it does take 5-10 minutes, (sorry!) and then a reboot


High-level description.


From the main form, it opens a webBrowser and writes an HTML page containing the JavaScript code to load the GE Plugin and around 20 JS functions to interact with GE that are called from later in the program using WebBrowser.Document.InvokeScript.

Load a GPS track:

Reads the selected GPS track from your track file (gpx, plt, nmea or limited kml) into an array of track point objects, one object per point

Does the polar transformation trigonometry to calculate and record the speed and direction of travel in each segment between each pair of points.

Generates a KML representation of the track and displays it in GE (using parseKml).

Start the animation.

When you start the animation, it calculates the expected (real-time) arrival time at each point and starts a timer with an interval of 100 ms.

Process the timer event

At every timer event, it does the trigonometry to calculate the target point's position (lat, long, alt) based on the speed and direction of the current segment based on the actual time elapsed since the last timer event.

Positions the target point model at this new point using invokeScript to call one of the JS functions (set up above in the webBrowser) which calls the getLocation().setLatLngAlt(lat, lon, alt) etc. methods to re-position the model in GE.

Calculates the camera's position (lat, long, alt, heading, tilt) using the currently active camera parameters (range, heading, tilt) relative to the target point and moves the camera to the new co-ordinates with a call to another JS function.

Bells and whistles

There are obviously many more features to the program (it runs to around 25,000 lines of code) that have not been described in this high level description. We have put a lot of time and effort into developing and refining the maths to provide a smooth and convincing animation that will remain "under wraps" for the moment

Release history

Web version July 2012

StarTraX on the web

After 12 months of hard work, we have re-written StarTraX, taking it from from the current version (Windows only, desktop application in Visual Basic) to a pure web application that now runs on the Apple Mac as well as the Windows PC.

Support for the current version (4.1) will continue until mid August 2012 after which support will be withdrawn and it will no longer operate.

Existing users are encouraged to move to the new version as soon as possible so that any issues can be resolved before the current version is withdrawn.

The user notes for the new version are being updated to describe the new web version, but meanwhle these user notes provide a reasonable explanation.

One of the many benefits of moving to the web is that it greatly simplifies and speeds up the process of releasing fixes and enhancements. No longer will you have to download and install the new version onto your computer to get the new version as each time you access StarTraX, you will automatically get the latest version.
We will continue to use best practice procedures to ensure the quality of all changes, including rigorous change management of source code and end-to-end testing prior to release.
We will continue accompany all enhancements and fixes, however small (or embarrasing!), with a note in this section.

July 16 2012 "Java open" Release

  • ADD - Use Java to open local files (to replace the slow file system file select with associated http POST to and from web site).
  • ADD - "Time Slider" on points and segments.
  • FIX - "Acft taxis above the ground" - no low flying below 120 ft.
  • FIX - "Hesitated on start" - reset system state only at start.
  • MOD - background of subsidiary screens is silver.
  • ADD - commence implementing "right-click" help link to Features doco.
  • ADD - more help info on login page.
  • FIX - "Sometimes the target point overruns the next point and the camera continues to swing."
  • ADD - Support for OziExplorer .plt file format
  • Version 4.1 August 2011

    This is a major release with lots of enhancements

    Version 3.10.3031 April 2011

    This is mainly a bug fix release, although there are a three minor enhancements.

    • Bug fix: "When using the "open with' facility to load a new track, the new track is opened in a second instance of StarTraX , not the existing instance - was lost in the previous version." Fixed, when you open a second or subsequent track, the new track is displayed in the original instance of StarTraX.
    • Enhanced the "open with" feature to retain the existing track(s) if multi-track selected.
    • Bug fix: "When changing from Surface to Aerial track mode (and vice versa), the track remains on the ground but the model and smoke appear in the air". Fixed, the track is re-drawn correctly on the surface or in the air.
    • Bug fix: "In the Multi-track Start Point Selection form, the start points aren't updated when you select a different track". Now, when you switch from track to track, the start points are updated to reflect the current track.
    • Add the update of Google Earth's unitswhen changing StarTraX's units.
    • Improve the detection of the start and end of a thermal when positioning the clouds.
    • Bug fix: "Track profiling hangs on tracks with lots of points". We now sample the track data to display around 1000 points in each view. There's no significant loss of detail, but great improvement in performance

    Version 3.9.3013 April 2011

    Version 3.8.3010 March 2011

    Version 3.8.2 February 2011

    • StarTraX is now able to be associated with a file type to "open with" from Windows Explorer. Double-click on your IGC or GPX file to open it directly in StarTraX.
    • Route and turn points displayed from IGC files.
    • IGC files load both the PRESALTTRK and GNSSALTRK and offer you the choice.
    • Cloud visibility can be toggled on and off.

    Version 3.8.1 January 2011

    • Cumulus clouds on top of thermals.
    • Manage process priority StarTraX to high, geplugin to low. Improves replay smoothness with minimal degradation of terrain refresh quality.
    • IGC files load the PRESALTTRK not GNSSALTRK
    • Fix to wait for new file's view to completely refresh before processing the track file. Stops ski tracks from loading as paraglider!
    • Deduce Glider theme when orbit path detected in an Acft-Light track.

    Version 3.7.3 December 2010

    • Display co-ordinates in dd (dd in degrees, mm as minutes and decimals) not dd.dddddd
    • Link camera panning with thermalling (gliding in climbing orbits). When thermalling, the camera pans continuously, at a rate determined by the turn angle. Not thermalling, the camera pans at a fixed speed, starting later in the segment.
    • Display wind direction in compass points (NE, ENE, E, ESE, etc) not degrees.
    • Detects screen size when displaying on systems with multiple screens.
    • Camera tilt is smoothed to eliminate jerky vertical movement.

    Version 3.7.2 December 2010 A major release

    Four new on-screen instruments:

    Speed with both analogue and digital display

    Compass - showing orientation and direction of travel

    Altitude - with a realistic aviation display

    Vertical speed (VSI) essential for gliding activities.

    For gliding tracks, it now has an analysis of wind speed and direction with on-screen indicators in the compass rose.

    Some replay enhancements including the introduction of banking for all tracks, improved camera smoothing of both heading and tilt.

    A third viewing option to add to "Follow" and "Observe" called "Lock" which locks the camera onto the moving target to provide a realistic replay experience.

    Plus a swag of minor fixes to little bugs.

    Version 3.6.6 October 2010

    A minor bug-fix release to resolve some issues in multi-tracking which under some circumstances caused all tracks to start at the same time.

    It also included an upgrade to the start point selection interface while multi-tracking.

    Attentive users will also note that we have removed the tilt (lean forward or back, "attitude" in aviation-speak) on the models when they are flying. We realized that in the "real world", the attitude of paragliders and other aircraft isn't directly related to their angle of climb, so tilting the models based on their angle of climb/descent wasn't very realistic.

    It's still there for ground-based activities like skiing, cycling and driving (in cars).

    Version 3.6.3 September 2010

    This was a minor bug-fix release including the removal of unused reference code to reduce the size of the installation file from 15 to 9 Mb.

    It coincided with, and was tested on Google's release of GE API

    Version 3.6.2 August 2010

    In looking for ways to improve the realism of the replay I have to walk the tightrope between the desire to display a great deal of detail and at the same time provide a smooth animation both of which put enormous loads on the computer processor to perform immense numbers of calculations at blistering speeds. The fact that a domestic desk-top computer can come close to achieving this is a constant source of amazement and awe!

    This release contains further enhanced the replay mechanism which have yielded a further major step up in replay smoothness. You can now zoom right into the cockpit of your fast moving aeroplane or hover 50 metres from your skier carving down a back run. You can follow your paragliders from a distance, or close in as they tightly circle in the thermal.

    It's not perfect, I know but given the practical limitations of the processor in your desktop PC or laptop and your broadband internet connection, it's pretty good (even if I do say so myself!).

    Experimenting continues with coding techniques to deliver even more realistic replays.

    Some major improvements have also been made to the multi-tracking feature, providing a simpler method of loading multiple tracks by making multiple selections from the Windows File open dialog box instead of having to load each track separately. The details are explained in the User Notes installed with the program update.

    Version information

    Document version date July 2012

    StarTraX Web Version