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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | RE: GISList: true v. magnetic North in GPS |
| Date: |
02/24/2003 06:10:41 PM |
| From: |
Pete Russell |
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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
======================================
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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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