I just thought I’d update my diary and give a shout for my trusty GT-31. Every few years I revive it and take it out for some data logging. This year I took it around the new Waterbeach development near Cambridge, UK. It worked perfectly. This is an amazing piece of kit.

One slight let-down was discovering that GPSBabel seems to have dropped support for the GT-31’s native SBP format. I thought that might be the end of my OSM career, but then luckily I found that I can still run the old NaviSys software on Windows 11. I can’t connect to the GT-31 over USB any more (why not?) but I can load the SBP file from the SD card and convert it to GPX. I can then drop the GPX file straight into OSM’s iD editor. Such great software!

I've recently added almost all of the house numbers in Landbeach, a village in England. I've also added house names, although these aren't rendered by Mapnik (yet). In case anyone is suspicious of the sudden appearance of such a large amount of data: I collected these numbers and names over a period of years for publication on the village web-map. I've only just got around to copying all that data onto OSM.

I had to take the GT-31 to bits again today, as it froze again. This is quite annoying, especially as I'm in rural Thailand where jewellers' screwdrivers are not easy to come by. And I had a whole day's exploration of Bangkok on the SD card. Luckily, I had split the day into 4 files, so I only lost the last file. I might even be able to retrieve that data from the internal flash memory, given a bit of time to fiddle with the NaviLink program.

I think I can see a pattern in the two freeze incidents that I have experienced so far. The unit seems to freeze if I use it without recharging the battery for a few days. The battery symbol on the display looks like about 90% full, but I suspect that this is a lie: the almost-full symbol actually means "on the brink of death". So from now on I am going to recharge it every day, regardless of what the battery symbol says.

Makes a change from South Cambridgeshire. There's more mapping to do here, particularly bits that Google Maps haven't done yet.

My compliments to user:sladen, who has drawn the new temporary Workington North railway station. After reading the Wikipedia article my first instinct was to fire up OSM and mark the thing myself, but sladen has already drawn it in great detail (osm.org/go/evNv0Jss ). Isn't OSM great?

Edit: URL fixed

Uh-oh. My Locosys GT-31 has just frozen for the first time, after working faultlessly for several weeks. It died some time after the "CARD FOUND" beep but before acquiring its satellite fix.

I don't want to void the warranty by taking the back off, so guess I'm going to have to wait for the batteries to run down. I wonder how long that will take.

I just did a 1-hour calibration of my voice recorder (Olympus VN-5500PC), ready for some audio mapping. It created a file 3601.5 seconds long, so that's a calibration factor of 3601.5/3600.0 = ~1.00042. Given that I probably didn't press the buttons to better than 0.5 s accuracy, that factor could be anything from 1.00028 to 1.00056. Still, in any case, that's better than 0.06% error.

At the end of today's logging trip I plugged the SD card from my GT-31 into the computer and, horror! the NMEA file was 0 bytes long.

At first, I gave up hope, and just used the few waypoints that I had successfully recorded to guess at a few path locations. At least I had something to show in OSM for all my effort.

Later, I returned to the SD card. I tried running PhotoRec on it, but the program found nothing relevant. Next, I wondered whether the GT-31's onboard data logger had saved the data, so I started NaviLink II and tried to read the log file. All I got was an error message (if you're listening, Locosys, I think we have a bug), but at least it told me that the logger's memory had some data in it. Then I decided to try writing the log file to the SD card, so I put the card back in the GT-31 and did a "Save to Card" from the Data Logger menu. This appeared to work, and I ended up with an SBP file on the card. I was then able to use NaviLink to convert this to GPX and upload it to OSM. Success!

So, thanks to the GT-31's belt-and-braces design, with logging to on-board memory at the same time as to the SD card, I didn't lose my data. It's great when a gadget gives you a second chance like this - it really feels like a dependable piece of kit now.

Epilogue: I don't know what caused the zero-length file. I admit that it's possible that I forgot to switch off the GT-31 before removing the card, but I'm not usually that careless.

There are many ways to get data from the GT-31 into OSM, and it can all get a bit confusing. Here is a very simple method for beginners (like me). It looks daunting, with such a large number of steps, but it only takes a few minutes. I'm assuming that you have already played with the OSM on-screen editor (Potlatch) and know how to use it.

Put a formatted SD card in the GT-31 and switch on.
Wait for the first set of beeps and the "Card Found" message.
Go the the Memory Card menu and set Log Switch=1 second, Min Speed=1 kmh.
Wait for the second set of beeps and the "New file" message. This means that the unit has started recording points.
Start your journey.
At the end of your journey, switch off the GT-31.
Remove the SD card and plug it into your computer.
Run JOSM and hit the "Open File" button.
Load the latest file from the SD card. It will be in a folder called GPS_DATA and have the extension .TXT. The track will appear in JOSM as a thin grey line.
Right-click on the name of your track file in the JOSM layers window, and select "Convert to data layer". Ignore the warning, because we're not going to upload the raw data to the map.
Delete any parts of the track that you don't want.
Right-click on your data layer again in the JOSM layers window, and save it as a GPX file on your local disk.
Close JOSM.
Open OSM in your web browser and log in.
Click the GPS Traces tab.
Upload the GPX file that you just created. A little picture of your track will appear on your GPS Traces page, marked with a red "PENDING" label.
Wait a few minutes and refresh the page. The "PENDING" label should have disappeared, meaning that your track has been added to the database.
Click the blue "Edit" link next the track name.
You are now in the OSM editor. Any existing OSM data will appear, together with your new track in light blue.
Edit OSM.
Save your changes.
You're done.

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My change to the A10 yesterday was a big mistake. I misunderstood the "highway=trunk" tag. After I had done all the work, I discovered a comment on the wiki (osm.wiki/Talk:Tag:highway%3Dtrunk) that explains how this tag is used. As users TomH and Richard patiently explained to me, OSM's interpretation of "trunk" is not the same as the UK Highways Agency's definition.

I have undone all my changes. Apologies to anyone who was confused by the sudden change of the A10 from green to red and then back to green!

I'm going back to what I do best: making GPS tracks.

As road spotters will know, the A10 has been detrunked (downgraded from trunk to primary). The bit from London to Cambridge was done in the 1990s, and the bit from Cambridge to King's Lynn in 2001. OSM still shows it as a trunk road, so I'm retagging it all. On the way, I've noticed a few more roads with delusions of grandeur, so I might come back to fix them later.

I'll head off some possible objections:

"But the road signs on the A10 are green." - Yes, I know. A green road sign means primary, not trunk. There is no special colour for trunk road signs. The colour system used by OSM is different: green for trunk and red for primary. I don't like this, but that's the way it is.

"But it looks wrong with all the green roads changed to red." - Sorry, but that's the map renderer's problem. The underlying data, i.e. the tags, must be made correct, regardless of what the renderer does with them. There aren't that many trunk roads, so the map is going to get a lot redder when people fix all the tags.

Correction: the entire A10 was detrunked in 2001. (Earlier, I mistook the realignment of a minor bypass in 1993 for the wholesale detrunking that happened later.) The relevant statutory orders were "The A10 London-Cambridge-King's Lynn Trunk Road (A47 King's Lynn to A14 Milton, Cambridgeshire) Detrunking Order 2001" and "The A10 London-Cambridge-King's Lynn Trunk Road (M11 Junction 11 to A505 Royston Hertfordshire) Detrunking Order 2001".

I received my new Locosys GT-31 yesterday. After about half an hour I worked out how to record a track (using TRACK mode). I wasn't sure if the GT-31 could be used successfully in a car, as it was marketed for walkers and surfers, but I found that it worked fine when placed in the space between the sunroof glass and the sliding inner sunroof cover.

When I got home, I uploaded my first track using Navilink II. The data appeared on the PC in several formats including KML and GPX. Just double-clicking on the KML file opened Google Earth and displayed my track, which was extremely satisfying and proved that everything worked! Next I downloaded JOSM and played around with the GPX version of the track, but as this was just a test I didn't upload anything.

At this point I was just capturing data into the GT-31's internal memory. I had bought an SD card, and I knew where the "save to card" option was in the GT-31, but I hadn't figured out how to interpret the data that was saved on it.

Today I took the GT-31 for a walk. This time, I went with the intention of capturing a real track for OSM, so I was careful to follow the footpaths without cutting any corners.

Unlike yesterday, when I settled for using the data from the GT-31's internal memory, today I was determined to work out how to use the SD card data. After all, I had paid for my 2 GB and I wanted to use it. The data on the SD card was in a file whose name ended in "_TRK.BIN". Promisingly, the Navilink II program, supplied with the GT-31, had a "_TRK.BIN" button under the "Misc" tab, but when I used it all I got was an error message: "ERROR_PORT". Normally, ports are what you use to talk to the GT-31, not to the SD card, so this message didn't make sense. Disappointed, I gave up on this approach.

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