Using Trails for iPhone

I think Trails is the best GPS tracking app for the iPhone that I've come across for plotting OpenStreetMap tracks. Here are a few things I've found:

I've mostly been walking or taking taxis, so the "minimum distance filter" set as low as possible (5m). I think this works better than having it switched off, as it reduces the overall number of points that need to be stored (see the next point).

I set the Required Accuracy to 80m. Even this is probably too high.

On an iPhone 3GS (running OS 3.1), if you track for more than 2 hours, creating several "Segments" along the way, the app gradually becomes less responsive. The Time Elapsed only updates every five seconds or so, and the map rotation becomes jerky, as does tapping or sliding on the interface. I think this is due to the number of points that have to be constantly updated on the display. Restarting the phone or the app doesn't significantly improve matters. It felt like a CPU problem, so on newer hardware it's probably fine.

When I first started mapping the town, I assumed that staying within the same "track", but making lots of "segments" would be the most effective way to work, as I could see which roads I had already been down. Unfortunately, the performance problems meant that I couldn't carry on this way.

So when the app became less responsive, I created a new Track, and set the old one to be a Background Track, thinking that this would still allow me to see where I had been, but maybe reduce the burden on the processor (as the user can't interact with the background track, so presumably it's just a bitmap or something?). This didn't work. The app was just as sluggish on a new Track with a complex Background Track, as it had been in the original Track.

So it seems that for large scale mapping, there's currently no easy way to do this in Trails, at least, not if you're using an iPhone 3G.

What's needed is a GPS equivalent to "onion-skinning" as used in many stop-frame animation applications. If all the former trails could be laid beneath the current trail as an image, even if this took some time to pre-process, it would be more useful than the current arrangement.

Also, if it was possible to switch off the map-rotation, this would save on CPU cycles, and make it easier for mappers to orient themselves! Having the map completely switched off would also solve the CPU problem, but being able to see the existing map is very useful.

Like I said, Trails is by far the best GPS app out there that I've used. The app almost never crashes, and the one time that it did crash, all my data was saved up until the very last GPS point that I was tracking! These are just some tips to make life easier for OpenStreetMap users. --Tomhannen 19:23, 26 June 2010 (UTC)