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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | Re: GISList: Garmin GPS & ArcView 3.1 |
| Date: |
04/09/2002 06:02:31 PM |
| From: |
Jim Gilpin |
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Hello Amin,
I've used both the e-trex and the more expensive Trimble Geo 3 with the
associated Pathfinder Office software for natural resource mapping. The Trimble
option allows for differential correction, and thus higher accuracy, but at a
much higher cost. For example, the Trimble package (GPS plus software) costs
about $7500 CND vs about $200 CND for the e-trex. The uncorrected e-trex data is
usually in the 5-10 m accuracy range. The normal or "code" corrected Geo 3 data
is usually in the 2-5 m range. Using the carrier phase shift data with the Geo 3
you can achieve differential correction to sub-metre accuracy.
So, I guess it depends on how flush you are. Higher quality data, ideally, is
nice to have. But single position (uncorrected) data, is simpler and cheaper to
acquire. At a 1:24,000 scale, the difference between corrected and uncorrected
data is hardly discernible. The Minnesota Dept. of Natural Resources has an
excellent free arcview extension (DNRGarmin) for uploading and downloading
Garmin GPS data to ArcView.
The errors in the original maps may exceed GPS error. Certainly scale errors in
standard aerial photos, from relief displacement, will be greater than GPS
error. You really should use orthophotos if possible. Given these other sources
of error, I'd recommend keeping the GPS data collection cheap and simple. Use
the e-trex.
"Davis, Amin" wrote:
> Hello, ALL
>
> I am seeking advice as to whether a Garmin E-Trex handheld GPS unit
> would be sufficient (in terms of relative accuracy) to do natural resources
> mapping, particularly mapping of trails, fences, & wetlands for a local
> nature conservancy. I use this same unit for quick & dirty mapping for my
> job (overlaying GPS points on 1:24,000 scale USGS quads or aerial
> photography). However, I have been asked to set up a GPS standard for this
> group and want to make sure that I don't need a more expensive GPS unit. I
> use ArcView 3.1 to map the GPS locations.
> The accuracy doesn't need to be survey quality (sub-meter).
> However, we want to be able to record coordinates and go back to these
> locations w/out ending up in another universe... Will this $120 Garmin GPS
> unit be sufficient or would you recommend an upgrade?
>
> Any Thoughts Would Be Appreciated!
>
> Thank You,
>
> Amin Davis
> Raleigh, NC 27622
> (919) 782-5511 Ext 171
>
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--
Jim Gilpin
Instructor: Surveying, GPS
Yukon College
Phone (867) 668-8763
Fax (867) 668-2935
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