A while ago, I picked up an Earthmate GPS LT-20 for my computer. It is intended for use with a computer; it has only a USB cable and a status LED, and is actually quite small. This means you can't take it with you hiking or anything.
Performance: The first thing I noticed about the LT-20 is how long it takes to get a fix. Reviews of the LT-20 usually omit the "warm fix" measurement, or the amount of time it takes to get a fix when it is powered on in the same exact place it was before. This is because the LT-20 lacks any memory of the last place or time it was used, and thus has to "start from scratch" each time you turn it on. This can be a bit of a pain, because it can take from two to five minutes to get the first fix.
Beyond that, the performance is okay. It very occasionally drops the fix for a few seconds, and a little more often (maybe a few times per hour) it will drop to a 2D fix. As it is a low-end GPS, the LT-20 has no provision for an external antenna, so all of these judgements were made with the GPS next to the window of the car. The accuracy of the GPS is again pretty good; I'm not very familiar with the expected accuracy of civilian GPS, but it seemed pretty good.
Linux compatibility: Being a Linux user, I ignored the included copy of StreetAtlas 2006 and tried to get the GPS working with Linux. With a little fiddling, I discovered how to get it to work:
- Build the
cypress_m8kernel module and load it. - Plug in the GPS.
- Check if
/dev/ttyUSB0exists. If it does not, runmknod /dev/ttyUSB0 c 188 0- Run
cat /dev/ttyUSB0and check that you can see some NMEA sentences come in.- Run
gpsd -f /dev/ttyUSB0 -n. - Run
Linux apps: As the LT-20 is very small and easy to hook up, it makes a great GPS for wardriving. On long car trips, I always have it plugged in with gpsd+kismet logging access points. It's also useful with gpsdrive for car navigation (the original, intended purpose of it), although you should know that gpsdrive, being open-source and lacking the access to commercial street maps that DeLorme and other companies have, doesn't give quite the same experience. It doesn't do turn-by-turn directions, but it puts you on the map and allows you to download maps from a handful of websites.
Conclusion: I would recommend the Earthmate GPS LT-20 with reservations: if all you need is a simple GPS for wardriving--that is, as a computer peripheral--then the LT-20 will fill that need cheaply. But if you need high accuracy, quick fixes, a portable unit, or on-board navigation, it's not for you.
Related: Navigation/GPS page at Tuxmobil.org. Tuxmobil is a site about Linux and Unix on mobile computers, and related hardware and software.
Buy the Delorme Earthmate GPS LT-20 at Amazon.com
