Ben, A follow-up to my message below...
The U.S. site is the NGS Opus-RS service: http://www.ngs.noaa.gov/OPUS/OPUS-RS.html The basic work-flow is: 1. Connect a Garmin GPS receiver (with an RS232 serial port) to a laptop 2. Execute "Async" and log raw GPS measurements for about 20 minutes to an hour 3. Use "gar2rnx" to convert the binary file from Async to a RINEX format file. 4. Upload the RINEX file to the NGS Opus service, wait for results. FYI,"Async" expects an RS232 serial connection (but you could change the source code to use a USB connection), so look for an older Garmin (ebay?) or a new one with the old style serial connection. Brent Fraser GeoAnalytic Inc. Calgary, Alberta ----- Original Message ----- From: "Brent Fraser" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, August 06, 2007 10:52 AM Subject: RE: [Geowanking] Cheap post-process DGPS - why not? Ben, With a $100 Garmin, some open source s/w, and some data from a base station, it's possible to get 20 to 30 cm accuracy. The easiest/cheapest situation is static post-mission processing. That means sitting on a point for 20 to 60 minutes, recording the needed information from the $100 Garmin, then computing the position of the point using the info from the base station. In most cases the base station data can come from the USGS. If you need dynamic real-time accuracy, then you would likely need to set up your own base station with another GPS receiver, a transmitter, and a receiver on the roving receiver (and more software). My need was to get sub-meter accuracy of 10 points to ortho-rectify a satellite image. I used a Garmin GPSMap60, "async" and gar2rnx software (http://artico.lma.fi.upm.es/numerico/miembros/antonio/async /) and the Canadian Precise Positioning Service (http://www.geod.nrcan.gc.ca/ppp_e.php). I don't have a link to the USGS site, but some intense Googling should find it... Brent Fraser GeoAnalytic Inc Calgary Alberta >> I have tried that approach with a pair of cheap GPSs and wrote the >> software to automatically do the add/subtract. Got absolutely rubbish >> results - even with two of the same model of GPS. I guess it is >> something >> to do with them not choosing the same set of satellites to use > > Darn it. Well, thanks very much for letting me know, you've saved me the > cost of buying that second unit to try it. :) > > -Ben _______________________________________________ Geowanking mailing list [email protected] http://lists.burri.to/mailman/listinfo/geowanking _______________________________________________ Geowanking mailing list [email protected] http://lists.burri.to/mailman/listinfo/geowanking
