Garmin GPS Car

admin answers:

If you have a module that connects to a PC, it will probably send a continuous stream of more or less incomprehensible “stuff”. With luck it will be in the NMEA format, considerable information is available on the web, a few sites I had bookmarked are in “sources” below. I haven’t actually done much with this since I use the Microsoft software, but i was curious about it, so i did a little looking.
I have a Pharos unit that came with Microsoft Streets and Trips™ that sends something like this:

first four lines are information about the Satellites that are in view
$GPGSA,A,3,21,22,18,03,26,,,,,,,,2.9,1.8,2.2*3D
$GPGSV,3,1,10,22,74,262,41,18,63,058,38,03,46,269,33,21,36,114,37*7A
$GPGSV,3,2,10,19,32,307,17,14,22,189,27,09,15,090,,15,11,111,*73
$GPGSV,3,3,10,26,07,034,32,24,03,114,*7C
next is the “Recommended Minimum Specific GPS/TRANSIT Data”
$GPRMC,115913.000,A,4744.0527,N,12438.1005,W,0.03,140.67,040807,,,A*74
and last is “Global Positioning System Fix Data”
$GPGGA,115914.000,4744.0527,N,12438.1005,W,1,05,1.8,16.3,M,-17.5,M,,0000*5B

note that Yahoo clips long lines so there is stuff missing, but this is just for example.

admin answers:

You have received two excellent answers so far. But I think you are still wondering how to do a differential land survey, right? Can you get hold of two GPS and two laptop PCs? It is then just a matter of registering the two positions and time sets and compare them later. I don’t know your budget for this project but you could e.g. Buy cheap PDA with GPS incorportated. You’ll find cheap ones like Mio and Acer. You’ll most probably find also freeware or shareware that reads the NMEA port of the GPS and creates a file with position and time. Then you might want to write your own application that reads both files, compare position for the same time and calculate the offset in whatever unit you want. Most probably when working at this accuracy, your geographical position is not important, only the relative one from one GPS to the other. But if you have a map reference, you can trace it from that. As a warning, don’t use GWS84 references on an old map. I know from experience that e.g. Nautical charts may be very relatively accurate but inaccurate to a common world reference such as GWS84.

admin answers:

On my Garmin Nuvi (and on most Garmin units) the Satellite information shows latitude and longitude along with satellite signal strength and altitude.

When the unit is turned on and tracking, there are signal strength bars on the top left (Nuvi units, at least). Touching the bars gets you to the Satellite Information Page.

I would suspect most GPS units have some similar way to display coordinates.