· th-d74 journal aprs gps hamradio

Light OpenStreetMapping with GPS

Now that lockdown is lifting a bit in Scotland, I’ve been going a bit further for exercise. One location I’ve been to a few times is Tyrebagger Woods. In theory, I can walk here from my house via Brimmond Hill although I’m not yet fit enough to do that in one go.

Instead of following the main path, I took a detour along some route that looked like it wanted to be a path but it hadn’t been maintained for a while. When I decided I’d had enough of this, I looked for a way back to the main path but OpenStreetMap didn’t seem to have the footpaths mapped out here yet.

I’ve done some OpenStreetMap surveying before so I thought I’d take a look at improving this, and moving some of the tracks on the map closer to where they are in reality. In the past I’ve used OSMTracker which was great, but now I’m on iOS there doesn’t seem to be anything that matches up.

My new handheld radio, a Kenwood TH-D74 has the ability to record GPS logs so I thought I’d give this a go. It records the logs to the SD card with one file per session. It’s a very simple logger that records the NMEA strings as they are received. The only sentences I see in the file are GPGGA (Global Positioning System Fix Data) and GPRMC (Recommended Minimum Specific GPS/Transit Data).

I tried to import this directly with JOSM but it seemed to throw an error and crash. I’ve not investigated this, but I thought a way around could be to convert this to GPX format. This was easier than expected:

apt install gpsbabel
gpsbabel -i nmea -f "/sdcard/KENWOOD/TH-D74/GPS_LOG/25062020_165017.nme" \
                 -o gpx,gpxver=1.1 -F "/tmp/tyrebagger.gpx"

This imported into JOSM just fine and I was able to adjust some of the tracks to better fit where they actually are.

I’ll take the radio with me when I go in future and explore some of the other paths, to see if I can get the whole woods mapped out nicely. It is fun to just dive into the trees sometimes, along the paths that looks a little forgotten and overgrown, but also it’s nice to be able to find your way out again when you get lost.


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