Actually, Curt and I worked through this some time ago. If you're not
careful, you'll get me into the GPS Lecture Series mode. In bygone
years on the APRS list, there were legions who groaned when that happened.
In general terms, you've got GPS accuracy (repeatability vice a known,
surveyed point) on the order of 6 meters. This has been the same ever
since DoD turned off selective availability in 2000. There are times
when it's better, times when it's worse, mostly due to satellite
constellation geometry.
If you use DGPS, RTK or WAAS, you should see an improvement of about
(not precisely) an horder of magnitude. Lots of receivers have WAAS now.
gc
Jim Tolbert wrote:
Running back to the desire for DAO packets..... I am assuming that
with standard APRS packets having 2 decimal places and DAO having 3
decimal places that I will be locating a particular GPS receiver to an
area that is an order of magnitude more precise. I am probably not
saying this correctly, but with the standard APRS packet, I have an area
of uncertainty of about 20' x 40' ( in northern Wisconsin, US (
N45,W92)). By moving to a DAO packet, I will have an area of
uncertainty of about 2' x 4'.
If I have a bunch of GPS receivers of the same type, can I assume that
the relative location is pretty good, even if the absolute location may
be off a bit? I am really primarily interested in relative positioning.
Since Xastir is really just plotting the data it receives, I am going to
post this query on the APRS group as well, but I wanted to be sure to
catch Gerry <grin>...........
Many thanks, all................... jt
--
Gerry Creager -- [EMAIL PROTECTED]
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843
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