If you're planning to turn your UAVs (or just R/C planes) into aerial mapping machines, you're going to want a GPS data logger. What they do is give position information that you can match with each of your shots, so you can properly align them into a mosaic and place it on Google Maps. Companies such as Pict'Earth can take a GPS log file and a zip file of a few hundred shots and turn them into a beautiful orthorectified Google Earth overlay like this
I've used two GPS loggers: the i-Blue 747
Bluetooth device from Transytems, and the Trackstick II
. The first I can recommend highly; the second I can't recommend at all. Here are the facts so you can make up your own mind.
1) The i-Blue 747
can be found for $70 at Amazon
. It's got 16MB of memory, tracks 32 satellites and has Bluetooth so you can use it for real-time telemetry and even have it drive an autopilot. It comes with rechargeable lithium batteries and is really small (approx 2.9" x 1.75" x 0.75"). The software does all the basics, including letting you download a saved GPS session to Google Earth or a CSV text file and let you see satellite positions and current reading in real time.
[Note: the software communicates with the device via a virtual Com port, handled by a driver. It can be a little tricky to figure out which Com port, however, so I suggest you go to your Windows device manager and see which port was assigned to the device and set the software to use that. On one of my machines it was port 5; on the other it was port 10; it depends on how many other drivers you've already loaded.)
It also saves GPS positions once per second, which is important when you're trying to match it with pictures you're taking at least that fast. In our testing, it aquired a satellite lock in less than minute and was rock-solid in keeping it, even when we just tossed the device randomly into an aircraft's instrument bay, buried under other electronics and bathed with other radio emissions. Basically, we've used this devices on dozens of flights, UAV and otherwise, and its performance has been top-notch.
2) The Trackstick II
costs nearly $150 at Amazon
. It only has 1MB of memory and only tracks 12 satellites. No Bluetooth, so it's just a logger with no real-time function. It requires AAA batteries, and is long and rectangular, about twice the total size of the i-Blue (4.25" x 1.25" x 0.9"). It has a built-in USB jack, so you can plug it straight into your PC (the i-Blue requires a standard USB cable). The software does essentially the same thing as the i-Blue's.
In testing, three serious problems cropped up with the Trackstick (aside from it being expensive, big, and badly underfeatured):
- It only records a GPS record every 15 seconds in low-power mode and every 5 seconds in high-power mode. Even at the highest, battery-draining settings, that's way too slow for aerial mapping.
- It takes forever to get a satellite lock. The first time, it took more than half an hour and subsequently it took more than three minutes.
- Keeping that satellite lock is a struggle, too. By having a terrible GPS chip that only sees 12 satellites, the Trackstick II suffers from frequent drop-outs and glitchy datapoints. We found it essentially unusable.
Basically, I can't understand why the Trackstick is even sold. It does nothing that the i-Blue747 doesn't do at half the price, and doesn't do other important things like Bluetooth, 1-second GPS sampling, and having a useful amount of memory. I'm sorry I bought it--avoid.