A Note on Accuracy
Kevin comments on the Android Market:
Not accurate. I was driving at 20mph and the app said I was going at 243mphs.
An Explanation
The speed displayed by RideTrac in this version is the exact value that’s reported by the built-in Android GPS software. What happens in the code is every time a location change is detected by Android, it notifies RideTrac and sends a packet of information called Location. One of the elements of Location is a speed value and that is the value that is displayed in RideTrac. When crazy values are reported, this is most likely because during that time the GPS location is inaccurate and jumping around a bit while the GPS tries to lock onto the satellites. If the GPS has you at one spot one second and at another 30-40 meters away the next second as it refines its position, it looks like you’ve been beamed up by Scotty and the reported speed reflects that. You usually notice this most often when you first turn the GPS on. You will see the blue accuracy circle around the current location start large and begin to shrink while the location gets refined. In good coverage this happens quickly, but if the configuration of the GPS constellation is poor or if you don’t have a clear view of the sky, refining the position might take a while.
In any case you shouldn’t see prolonged, grossly inaccurate speeds unless you are in a very poor coverage area. Also, the prime function of RideTrac is to record your rides and the instantaneous speed is not part of what is recorded. If you do see very inaccurate speeds while in a good coverage area, let me know and we’ll see if something else might be going on there.
The next version of RideTrac will attempt to do some better filtering of the GPS data to avoid this sort of thing, but remember it is dependent on the built-in GPS accuracy no matter what. Filtering can only remove blunders, not make the GPS any more accurate than it actually is.
Thanks for the feed back.
If you leave the cell tower location service on while RideTrac is running, you may experience this “beaming” effect by miles at a time. When I inadvertently left the cell tower location service on during one of the test rides, RideTrac managed to rack up about 100 miles worth of ride data in the first 5 minutes of the ride.
@Adam
By “the cell tower location service”, do you mean you have the “Use wireless networks” global setting turned on? I guess I’ve never tested RideTrac with that turned on. I’ll look into it.
@dave
The “use wireless networks” setting allows for rough location estimation based on the known locations of cell towers within the phone’s range. Leaving this on while RideTrac is running caused, at least on my phone, the route to jump all over the place.
@Adam
Thanks for pointing this out. I verified it myself and you are correct. I am working on the next upgrade which addresses this issue. Here is the situation in a nutshell:
RideTrac 1.0.1 ignores what the location provider is (GPS, cell network, etc) and simply assumes that all providers are equal and consistent. Now I know this isn’t true. The next version of RideTrac only uses locations from a single, “best available” provider at a time. This means if you have both GPS and wireless network location ON and both are in range, then GPS will be used and wireless ignored. However, if you lose GPS signal for some reason but still have wireless, then RideTrac will automatically use wireless. I’m testing this out now and it seems to be working. Look for a new version this weekend addressing this plus a few other issues that have cropped up.
FYI: Version 1.0.2 is now released and fixes this problem.