[Xastir] Question on site survey

[Gerry Creager (N5JXS)]

Excellent point.  However, I'm pretty familiar with how the OnCore does 
its math, and I've compared it to post-processed data from Trimble and 
Ashtech receivers, producing documented NAD83 coordinates.

The GPS ICD (ICD-GPS-200, currently, I think [the docs are at home or 
with KJ5O] REV C) tells you how to do the math.  If you don't do it 
right, you get a different answer.  Magellan had a conscious decision to 
use integer math and take some shortcuts in their matrix manipulations 
to save money overall, and try to capture the sub-$100 market.  from my 
perspective, that was a mistake and it took a long time for them to 
decide to do it right.

If a programmer took an unauthorized shortcut in the Garmin code, well, 
that'd be problemmatic.

gerry

Brian D Heaton wrote:
> Jack,
> 
> 	Do you have access to a 3rd GPS from a 3rd vendor (or even a few
> more)?  I think it would be interesting to see if two agree and only one
> disagrees.  That might give you a few more datapoints.  
> 
> 			THX/BDH
> 
> 
> 
> On Mon, 2003-12-08 at 04:43, Jack Twilley wrote:
> 
>>WARNING: Unsanitized content follows.
>>WARNING: Unsanitized content follows.
>>-----BEGIN PGP SIGNED MESSAGE-----
>>Hash: SHA1
>>
>>I've mentioned on xastir-dev that I'm running a site survey with my
>>M12 Oncore GPS in an attempt to identify precisely where my station is
>>located.
>>
>>I've noticed something disturbing about the survey -- I've been
>>collecting data for roughly five days and my original estimate
>>(gathered from my Garmin GPS III+ in my car, and from Mapquest, etc.,
>>with my address) is reasonably accurate in latitude and altitude but
>>not longitude.
>>
>>The amount of error in longitude is within 0.2% of 100 meters, with
>>the Oncore thinking it's 100 meters west of the Garmin's location.
>>
>>That nice round number looked suspiciously like a datum problem, but I
>>checked with the @@Ao FF command, and I received "ID 49", which
>>corresponds with WGS-84 according to the Oncore documentation.
>>
>>Suggestions?
>>
>>Jack.
>>- -- 
>>Jack Twilley
>>jmt at twilley dot org
>>http colon slash slash www dot twilley dot org slash tilde jmt slash
>>-----BEGIN PGP SIGNATURE-----
>>Version: GnuPG v1.2.3 (FreeBSD)
>>
>>iD8DBQE/1EfbGPFSfAB/ezgRApmWAKDnzo92s/Dk24C5wB0wPgWTlzMcKQCdF66P
>>8kCSBqP9JEkZwJhCyTQkMbk=
>>=7igU
>>-----END PGP SIGNATURE-----
>>_______________________________________________
>>Xastir mailing list
>>Xastir at xastir.org
>>http://krypton.hscs.virginia.edu/mailman/listinfo/xastir

-- 
Gerry Creager -- gerry.creager at tamu.edu
Network Engineering -- AATLT, Texas A&M University
Office: 979.458.4020  FAX: 979.847.8578
Cell: 979.229.5301    Pager: 979.228.0173