Deternining when GPS data is good

Hi!

I am new to GPS's and I am writing software application for the
PocketPC to get the location using I-Blue737 Bluetooth GPS. I can get
and parse the NMEA string okay and get the latitude and longitude
values, but I'm not sure when the location is within the 2D-RMS spec
of less than 3 meters. Can I assume after the cold start time, the
data is accurate? What do GPS applications typically do to determine
when the data is good? Any help would be appreciated!

Thanks a lot!!!
Anne

Hi,
if you are reading the GGA sentance :

$GPGGA,074851.00,3115.453366,N,12108.636274,E,2,05,2.0,0.738,M,9.689,M,
1.0,0012*76

Value after "E" is the working mode of your GPS (2 here).
And with the following code :

0 - Invalid
1 - GPS fix
2 - DGPS fix
3 - I can't remember but something like GPS SPS mode
4 - RTK fix
5 - Floating or RTK initialisation.

You will get some other informations on the following link :

http://aprs.gids.nl/nmea/#gsa

Cheers

http://utilsea.free.fr

Anne wrote:

Anne--You will only know what is typical of your instrument by
testing against a "known" surveyed position. If a receiver could
actually "know the magnitude and direction of its error, that
information could be applied to correct the error.
http://edu-observatory.org/gps/gps_accuracy.html

Some receivers (and signals used) are more accurate than others.

wrote:

But then, of course, if you knew that, you wouldn't need
the GPS device, hahahahaha!

wrote:


If you were using it in conjunction with a paper map, you would.

--
Alan White
Mozilla Firefox and Forte Agent.
Twenty-eight miles NW of Glasgow, overlooking Lochs Long and Goil in Argyll,
Scotland.
Webcam and weather:- http://windycroft.gt-britain.co.uk/weather