GPS on Motorcycle

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On my motorcycle I use a GPS (Global Positioning System) handheld for navigation. It cannot substitute a map completely, but it is a nice toy. The main reasons for me using it are:

On my Pyrenees and Scotland pages, you can find lots of tracks and useful waypoints recorded on my trips. And on my video page you find two other nice video captures showing the GPS device in use.
My GPS system consists of the following components (21.7.2002). Most of the software is freeware or shareware:

Convert Tiled Maps from Web to Plain TIFF Files

This is just a short example of my automated process to construct maps from map tiles of online map servers like Terraserver.
  1. Goto Terraserver and find out min/max X/Y-coordinates and URL rules of desired region by analyzing the HTML-code of the frame displaying the map tiles.
  2. Update gen_lynx.awk with desired coordinates and URL
  3. Run awk -fgen_lynx.awk >gen_lynx.bat to generate script for downloading all the map tiles needed.
  4. Run gen_lynx.bat to actually download the map tiles. Script can be split into several batch files to speed up the download.
  5. Convert all downloaded tiles to GIF.
  6. Update gen_gif.awk with tile numbers.
  7. Run awk -fgen_gif.awk >gen_gif.bat to generate script for combining all the GIF tiles into one big animated GIF
  8. Run gen_gif.bat, which creates a single huge animated GIF (all.gif) containing all map tiles at correct positions.
  9. Load all.gif into gimp and combine all image layers (single GIF tiles) to one layer and save as TIFF image.
  10. Find out coordinates of image corners on Terraserver and use them to calibrate the new map.

GPS Mount

You can get commercial GPS holders in different shops. The most popular ones are from Touratech, I think. They are very stable and reliable. You surely can participate at Paris-Dakar with them. This makes them rather expansive. For normal touring on streets and gravel roads, a simpler solution is enough. I created my own simple and cheap holders for motorcycle and car. In both cases it simple consists of: Fixed this way, I never lost the GPS device, even on heavy gravel roads. A further advantage is, that you can still easily grab around the GPS device with your hand while pressing the buttons with your thumb. This is much more ergonomic than just targeting with a single fingertip to the small buttons. The first picture below shows the GPS mount above the instruments of my motorcycle without GPS device. On the second picture you can recognize the aluminium part below the GPS device through the windshield. The third picture is animated and shows the front view of my bike with windshield and instument cover taken off. On top of this page you see how it looks with GPS device. And clicking it, you see a little MPG movie showing how easily it can be operated. By the way, if you wonder about the camcorder on the tankbag, just visit my video page to find out more about it.

Please consider security issues when searching a good position to mount your GPS device. Don't mount it in a low position. You won't see the road any more when playing around with your GPS while driving. If you mount it in a higher position, you will keep the road at least in your peripheral view. The probability is higher, that you recognize any obstacles or other vehicles early enough.

Selective Availability

In the early years of the GPS system, the US operated two different signals on their satellites: The high precision military signal and the low precision civil signal. The civil signal just had an artificial error put on it, which decreased precision. This mechanism was called "selective availability". In May 2000, it was turned off. Since then, the civil and military signal basically have the same precision.

A friend of mine (Glen Reiff) informed me just some hours before the US turned off selective availability. After reading the press release of the White House, I immidiately installed my GPS on my balcony and started a fixed point track to see the decreasing error (1 track point/minute). You can download an Excel sheet with a detailed analysis of the track (average error, error distributen with and without SA). The following simplified chart shows, how position error significantly decreased from about 40m to about 8m at 6:00 AM MESZ on 2.May 2000


Rolf Schlagenhaft, created 17.9.97, last update 21.7.2002, accesses since 4.9.2000