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| GeoCommunity Mailing List |
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| Subject: | Re: GISList: true v. magnetic North in GPS |
| Date: |
02/24/2003 06:44:49 PM |
| From: |
Richard Ash |
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I would concur with Pete that this setting should not effect positioning.
It would effect the azimuth readings you receive while navigating.
If ALL (versus a percentage being anomalies) the points are consistently off
the same distance and direction, the problem is most likely a mismatch
between coordinate system/datum of the GPS coordinates and your basemap
layers. This trick is finding where the mismatch originates.
Note, that the projection settings on many GPS units only will determine how
the data is viewed. The data may actually be stored in a default coordinate
system/datum - typically Lat/Lon, WGS84.
Good luck.
Richard Ash
GPS Consultant
_______________________
Products, Consulting and Training for GPS/GIS/SURVEY
Specializing in GPS and Laser Range Finder Technology
Global Mapping Technology
1107 NW Oak Avenue
Corvallis, OR 97330
email: <gmtgps@peak.org>
----- Original Message -----
From: "Pete Russell" <wmrussel@excite.com>
To: <ifischho@Princeton.EDU>: <gislist@geocomm.com>
Sent: Monday, February 24, 2003 4:10 PM
Subject: RE: GISList: true v. magnetic North in GPS
>
> Hi Ilya,
>
> I can't answer all your questions about your error, but declination should
not have any effect on the accuracy of your points. Let me know if you hear
a differing opinion.
>
> Cheers,
>
> Pete
>
> ======================================
> Forester
> Russell Precision Mapping Inc
> GIS, GPS and Timber Management
> Based in Richmond, VA and Tuskegee, AL
> Office: (804) 320-2254
> Mobile: (804) 356-MAPS
> ======================================
>
> ---
>
> Hello,
> I am a grad student in ecology at Princeton. My thesis is on zebra
> movement and cognition. My field site is in Laikipia District, Kenya,
> slightly (<0.5 degree) north of the equator. My GPS data from last
> summer, collected with a Garmin 76, have errors of several hundred
> meters, relative to existing topo maps produced by the British army. I
> think the error is consistent in direction and distance, but I don't
> have enough points for comparison to be sure yet. I'd like to figure
> out these errors prior to using my georeferenced habitat data for
> analyses of ASTER images. I collected my GPS data in Clarke 1880
> spheroid, Arc1960 datums, the same projection as the topo maps. I am
> not sure whether I had the GPS set for true North or magnetic North when
> I collected the data last summer, but should be able to find this out
> soon with help of someone in Kenya. I'm writing to ask if there exist
> lookup tables for converting GPS data collected with one declination to
> the coordinates for the other North reference, for a given lat/lon
> location. Is it just a linear transformation? Thanks very much for any
> input. cheers,
> Ilya
>
>
>
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