How many speedometer applications does the iPhone 3G need? You tell me. I wanted a speedometer application that was very simple and also let me know where I was even out of reach of a cell tower. So I wrote one.
The most important requirement was that I could use it on my motorcycle. That meant no fancy displays, options, or other wizardry. In fact there is only one button for this app. You tap it to toggle between MPH and KPH. That's it. The button doubles as a label to remind you whether the speed is in MPH or KPH.
The basic, easy to read display gives you your speed, course, and location. While the application is running, your screen won't shutoff, so you don't have to disable your screen autolock.
JUST DON'T STARE AT IT WHILE OPERATING A MOTOR VEHICLE!!!
Requires GPS & iPhone OS 3.0
Doesn't work in Airplane Mode.
Some words on accuracy. If you compare the speed reading to your car, motorcycle, or other vehicle, it will usually be different. It could read higher or lower. Under acceleration the GPS is likely to lag.
This is all normal. The GPS will only update the display when you've moved about 10 meters (depending on signal strength) or when it gets a more accurate reading. There is also a small amount of lag while the reading settles down during constant speed.
Bottom line is that you should not count on the speed readings being super accurate or consistent in their error. The same applies to your position. The display of precision used to show your position exceeds the actual accuracy capabilities of the device.
That said, I did write this application for my use. If I find ways to improve the accuracy on an iPhone 3G, which is my everyday use device, I will. Any improvements will of course be uploaded. Perhaps the accelerometers can be used to augment the speedometer. Perhaps there are other ways to work with the available data.
Some words on the display. I know that the other speedometer applications use fancy graphics presentations. The display for this application was chosen to provide information quickly in all lighting conditions. Mucking around with or staring at an iPhone display is NOT something you want to be doing on a motorcycle!