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| Subject: | Re: GISList: Hawaii GIS & GPS coordinate discrepancy |
| Date: |
08/01/2002 08:51:40 AM |
| From: |
Buzz Hiller |
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Has anyone checked these errors in terms of parts per million ? This might
reveal a conversion process error...for example, using 2.54 CM to the inch
instead of 2.5400XXX. This example is probably not an issue, but
consistency in the percentage error might yield further insight to the
issue.
Just some ideas..
BH
----- Original Message -----
From: "Peter Earls" <earlsp@okstate.edu>
To: <gislist@geocomm.com>
Sent: Wednesday, July 31, 2002 8:37 PM
Subject: Re: GISList: Hawaii GIS & GPS coordinate discrepancy
> Thomas,
>
> Are your UTM coordinates for roads generated directly from the GPS
> receiver or it's software as opposed to projecting lat-longs in a GIS? I
> ask because I have found a discrepancy in Oklahoma that may be related.
>
> I have found that UTM NAD27 coordinates generated by several makes and
> models of GPS receivers (Trimble (including Pathfinder Office software),
> Garmin, Magellen, and Rockwell using the military P code) generate
> coordinates that are consistently 27 m east of the same UTM coordinates
> given by ESRI software and by the UTMS program (
> http://www.ngs.noaa.gov/PC_PROD/pc_prod.shtml ) when I project the
> lat-long coordinates read from these receivers. I found this to be the
> case so far in 2 locations about 75 miles apart.
>
> I don't know why this discrepancy exists yet, but a surveyor has told me
> that NGS sets the standards, so supposedly the UTMS program should be the
> 'correct' coordinates. But UTM coordinates from GPS overlay considerably
> closer (5-6 m difference on average) on DOQs than the ESRI and UTMS
> coordinates.
>
> I have yet to find any datum/spheroid differences that amount to this
> distance in Oklahoma (NAD27 and NAD83 differ by ~200 m mostly in the
> north-south direction here).
>
> - Pete
>
> ==================================================================
> Peter Earls
> Oklahoma State University
> earlsp@okstate.edu
>
> On Wed, 31 Jul 2002, Mike Flannigan wrote:
>
> >
> > It sounds very familiar. I noticed on a trip to Hawaii this year that
> > the entire GNIS database of features is off by the same, consistent,
> > ~100 meters you notice. As I recall, features are really east of the
> > location given in GNIS. Not sure what the problem is, but I
> > suspect it is datum related. GNIS appears to be NAD27 for the
> > lower 48, but it's not well documented in my version.
> >
> >
> > Mike Flannigan
> >
> >
> > Thomas Harris wrote:
> >
> > > Hi List:
> > > We are having some difficulty with out Hawaii GIS. I received USGS
> > > DRG's that are in UTM NAD27. Overlaying our Hawaii roads coverage
> > > reveals a uniform offset in the DRG data of over 100 meters. We have
> > > confidence in our road data because of field validation with GPS. I
> > > suspect that the problem is perhaps unique to Hawaii. Does this
> > > problem sound familiar to anyone working with Hawaii data?
> > > Thanks in advance,
> > > Thomas
> >
> >
> >
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>
>
>
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