Conversion Tools
When I got my GPS, I learned that there are a variety of different formats of GPS data. Some tools prefer to work with a certain version. Now that Google Earth is on the scene, GPX seems to be emerging as a dominant format, and as it's XML, it can be easily processed using a variety of methods. I've developed several methods of converting between GPX and various other formats. Most of these operate with gpsbabel or files produced by gpsbabel.
Collapsing multiple trk elements
When my Garmin eTrex loses its signal (when walking through heavy woods, for instance), it starts a new segment. When gpsbabel reads out the information, it produces a GPX file with multiple trk elements. This makes the file cumbersome to deal with when imported into Google Earth, because each segment shows up separately, and there may be dozens.
According to the GPX specification, separate trkseg elements should be started when the GPS signal is lost and regained. The trkseg elements still exist within a single trk element, which represents the trip as a whole. This XSLT stylesheet collapses multiple trk elements into a single trk element, within a trkseg.
The easiest way to run this is with xsltproc:
xsltproc gpx_trkseg_collapse.xsl your_gpx_file.gpx > transformed_gpx_file.gpx
Download gpx_trkseg_collapse.xsl
Converting gpspoint files to GPX
This is a very simple Python program to convert gpspoint programs into GPX. Before I started using GPX, I used some programs that required gpspoint, and ended up with lots of older GPS files in gpspoint format. It's probably possible to write gpsbabel style files to do this conversion, but I was more successful with Python. To perform the conversion:
gpspoint_to_gpx.py your_gpspoint_file.gpspoint > your_gpx_file.gpx
The input file is assumed to contain either a track or a list of waypoints, not both.
Converting GPX files to gpspoint
If you need to use GPX data with a program that only accepts gpspoint, you can convert it back using a gpsbabel style file. An example:
gpsbabel -i gpx -f input_file.gpx -o xcsv,style=gpspoint_track.style -F output_file.gpspoint
Download gpspoint_track.style for converting tracks, or gpspoint_waypoint.style for converting waypoints.