OGPS

Online Help

About this help page

This is an online help page that may be updated over time. If you might need help while you do not have Internet access (while traveling, for example), you should save or print a permanent copy of this page.

Last updated: June 14, 2009

What you need to use the application

To display one or more tracks over an orienteering map, you need two things:

An image file containing your map. This can be obtained by opening the OCAD file and exporting an image, or by using a flatbed scanner or digital camera. A resolution of about 200 dpi is recommended, but not required.
One or more files containing the tracks you want to analyze. These track files can come from Garmin Training Center or they can be standard GPX files. Later versions of Garmin Training Center allow you to export a single activity, rather than your entire history.

Starting a new OGPS file

To align a track with a new map, follow these steps:

If an OGPS file is already open, click File > New.
Click File > Open Map Image and find your map image file.
Click File > Load Tracks, find your track file, and then select which track you want to load.
Click on the Calibration tab if it is not visible.
Find two points of your track (such as lap points or sharp corners) that you can accurately place on the map.
Using the right mouse button, drag each track point to the corresponding map location. This will create calibration points.
If necessary, create more calibration points to improve the alignment.
To manually edit or delete a calibration point, left-click on it to select it.
To see what effect different calibration points have, you can enable/disable them using the "Use this point" checkbox.
Once you get your track aligned properly, be sure to save the OGPS file.

Some noteworthy information:

It is possible to load multiple tracks (from multiple files) at once. You don't have to repeat the track loading procedure.
Tracks can be loaded from other OGPS files as well as from Garmin Training Center and GPX files.
Lap points and heart rate data are not loaded from GPX files.
Within the Calibration tab, holding down the Shift key disables the automatic selection of the nearest track point. Instead, the coordinates of wherever you click (relative to the track) are taken.
The keyboard shortcuts Ctrl+PgUp and Ctrl+PgDn can be used to cycle through the calibration points.
The mouse wheel and the keyboard shortcuts Ctrl+Up and Ctrl+Down can be used to zoom in and out.

Control circles

Circles with names or numbers can be added to the map using the Circles tab. Read the instructions on this tab for details.

Once the map is calibrated, it is possible to export the circles into a GPX file as waypoints. The waypoints can then be sent to your GPS using a program such as Garmin MapSource. This feature may be useful for course setting. However, if you decide to use this feature for course setting, note the following:

The waypoints are exported using the current calibration settings. Thus, they could be inaccurate, especially if they are not near any calibration points.
You may end up with poor courses if you follow your GPS while checking control locations. Without actually orienteering, you may not notice map inaccuracies or other factors that would make it difficult to find the controls without using a GPS.

It is also possible to import waypoints from GPX files. When doing so, it is especially important to note that the circles are stored by their map (x, y) coordinates. Thus, when waypoints are imported as circles, the current calibration settings are used to position the circles on the map. Changing the calibration settings afterwards will not move the circles.

Display settings

You can use the Display tab to adjust the color and size of the tracks and the various point features drawn on the map.

Sometimes, the best way to make the features stand out is to shade the map. The shading slider on the Display tab makes the entire map image closer to the shading color. To make the map image darker, for example, set the shading color to black and move the slider a few notches to the right. (Moving the slider all the way to the right will completely replace the map image with the shading color.)

Route playback

Using the Playback tab, you can see the tracks played back at a proportional speed. For example, at a playback speed of 60X, each minute of orienteering is replayed in one second. Note that you can manually reposition the moving slider at any time (during playback or while playback is stopped).

If you have multiple tracks, selecting the "Mass Start" option will make all the tracks start at the same time. This is useful for comparing races and seeing where competitors gained or lost time. Deselecting the "Mass Start" option will make the tracks play with respect to the date and time that they were recorded. (Any periods of time not covered by any track will be skipped.)

Track tab

On the Track tab, you can select how the tracks are colored. The tracks can be colored individually (each track gets a different color), or according to speed, elevation, or heart rate. The colors used can be selected on the Display tab. When coloring the tracks according to speed, elevation, or heart rate, the range of values matched with the colors is automatically set. The lowest and highest 5% of values from each track are disregarded.

While this tab is visible, you can right-click or right-drag on a track to obtain various information about a track point or track segment. This information has many uses, including the following:

Getting the date, time, coordinates, and other data of a single track point
Seeing how much time was lost due to mistakes
Comparing distances traveled to straight-line distances
Seeing the average speed, elevation, or heart rate over part of a track

This tab also allows you to edit tracks. Lap circles (which are automatically numbered) can be added to and removed from tracks by pressing the L key while individual track points are selected. Selected track points can be deleted by pressing the Delete key. Deleting all of a track's points will delete the track itself.

Opening and saving OGPS files

After aligning a track with a map, you should save the OGPS file. Then you can see your route later without recalibrating the map. Furthermore, if you run a race in the same area as a previously recorded race, you can then open the OGPS file for the previous race and simply replace the track with your new one.

The following information is saved in OGPS files:

The name of the map image file
The location of the map image file if it isn't in the same folder as the OGPS file
The calibration points
The control circles
The tracks

The following information is not saved in OGPS files:

The map image itself
The display settings

It is recommended that you keep the map image files in the same folder as your OGPS files. This way, you can move files around without having to relocate map image files.

Files saved by versions 1.0.0 to 1.2.0 of OGPS do not contain elevation or heart rate data. This data can be obtained for past races by reloading the tracks.

Exporting images

To export an image of the map and tracks, select "Export Image" from the File menu and then choose which combination of map area and zoom level you want. You can choose from a variety of image formats. The PNG format is probably best if the map image was exported from OCAD. The JPEG format is probably best if the map image came from a scanner or digital camera and a small file size is desired.

The Export Image feature exports everything that would appear on the map. This includes any temporary points shown while calibrating the map or while obtaining track information. If you do not want such points included, make sure that none are being displayed.

Factors affecting accuracy

Tracks normally align fairly well with orienteering maps once a few calibration points are added. Sometimes, however, it is difficult to make tracks align with a map. This can be caused by the following factors:

Map inaccuracies: Although a map may be suitable for orienteering, it may not accurately represent the terrain as an aerial photograph would. Corrections or additions done by fieldwork alone can be significantly off.
GPS inaccuracies caused by tree or cliff cover, ionospheric distortion, or lack of satellites. See the Wikipedia article on GPS for more information. GPS inaccuracies are more noticeable on smaller scale maps.

About the application

OGPS was developed by Thomas Graupner. The matrix transformation module used in earlier versions was written by Dave Graupner.

This application was made primarily for the personal use of the developer. The current version is freeware, meaning that all of its features are completely free to use forever. If you wish to make a donation, please see the donations page.

Legal disclaimer: This application is provided "as is" with no warranties of any kind. Use at your own risk.

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