Re: GPS and WM5 SirfIII problem

Hi,

Speed is in the 7th field of the GPRMC sentence, which in you sample data
varies from 0.66 to 2.88, down to sentences that show only 0.00. The GPGGA
(also 7th field) sentence specifies the number of satellites in view. So,
your code is interpreting the output correctly. That is, the NMEA-0183
GPRMC sentence DOES indicate 0 speed -- if the associated GPGGA sentence
shows 4 or more satellites in view, then there is a fault in your receiver.
Some receivers are programed to filter out very low speeds, where the actual
speed is zero, but the algorithm that determines it from GPS location
detects variation of location as speed.

I speculate that this may be happening in your receiver, but because of some
sort of bug, this low speed variation (noise) isn't filtered reliably. I'm
not sufficiently familiar with the internal workings of the SIRFIII to say
if the fault is with the chipset, or with some allied processor -- or,
perhaps, you just have a bad unit.

***

--
Richard Grier, MVP
Hard & Software
Author of Visual Basic Programmer's Guide to Serial Communications, Fourth
Edition,
ISBN 1-890422-28-2 (391 pages, includes CD-ROM). July 2004, Revised March
2006.
See www.hardandsoftware.net for details and contact information.


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