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 12, 2008

What you need to use the application

To use OGPS, 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.
A history file from Garmin Training Center containing your track. Later versions of GTC allow you to export a single activity, rather than your entire history.

Using the application

To display your track over your map, follow these steps:

If an OGPS file is already open, click File > New.
Click File > Open Map Image and find your map image.
Click File > Load Track, find your history file, and then select which track you want to load.
Click on the Calibration tab if it is not visible.
Click on Track View to display the Track View window. Start, finish and lap locations are shown as green circles under the default display settings.
Find three points on your track (such as lap points or sharp corners) that you can accurately place on the map. These points should be far apart and not in a straight line.
Add each of the first three calibration points as follows:
* In the Track View window, zoom in on the point and click on it while holding down the Control key.
* In the main window, zoom in on the corresponding place on the map and click on it while holding down the Shift key.
* To identify the point, type in a point name (such as "Control 5" or "Trail Junction").
* Click on the Add Point button to add the calibration point.
Once three calibration points have been added, your route should appear on the map. You can now close the Track View window as you no longer need it.
If the route is inaccurate in places, you can add more points by following the same procedure as in step 7, with the exception that track points can now be selected within the main window.
If you need to adjust a point, do the following:
* Select the point in the list.
* Change the Map/Track coordinates by manually editing the fields or by clicking on the map while holding down the appropriate key.
* Click Update Point.
To see what effect different track points have, you can enable/disable them using the checkboxes beside their names. Points that skew the rest of the track may be inaccurate and should be disabled or deleted.
Once you get your track displayed properly, be sure to save the OGPS file. Then, once you run another race on the same map, you can simply open the file and load your new track.

Control circles

If you took laps at each control, the lap points will appear on the map as small green circles by default. (To have them displayed differently, adjust the display settings.)

If you didn't take laps at every control and your map image doesn't show the control locations, you can manually add control circles using the Circles tab. Read the instructions on this tab for details.

Display settings

To make it easier to see your route and control locations, you can use the Display tab to adjust the color and size of everything the program draws on the map.

Sometimes, however, it can be hard to see the features regardless of their coloring. In such a case, you can make the features stand out by shading 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 (which it is by default) and then move the slider a few notches to the right. Note that 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 your route 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.) This way, you can find out exactly where you were at any given time.

Track information

On the Track tab, you can select how the track is coloured. The track can be coloured according to speed, elevation, or heart rate. The colors associated with low, medium, and high values can be selected on the Display tab. The range of values is automatically calculated, with the lowest and highest 5% excluded.

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

Getting the 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 the track

Opening and saving OGPS files

After aligning your track with the 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 track and the lap locations
Elevation and heart rate data

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 track, 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 none are being displayed.

Factors affecting accuracy

Tracks normally align fairly well with orienteering maps. Sometimes, however, they don't and adjusting the calibration points doesn't help. 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.

A calibration point in an inaccurate area of the map may improve the track in that area, but it may skew the rest of the track. It is probably best to avoid using calibration points that differ significantly from the others.

About the application

OGPS was developed by Thomas Graupner. Its matrix transformation module 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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