|
|
| GeoCommunity Mailing List |
| |
| Mailing List Archives |
| Subject: | Re: GISList: Hawaii GIS & GPS coordinate discrepancy |
| Date: |
07/31/2002 07:32:27 PM |
| From: |
Peter Earls |
|
|
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
>
>
>
> To unsubscribe, write to gislist-unsubscribe@geocomm.com
> ________________________________________________________________________
> Setup a GeoCommunity Account and have access to FAST DataDownloads
> and Premium Career Posting at a discounted rate!
> https://www.geocomm.com/cgi-bin/accounts/login
>
> On-line Archives available at
> http://spatialnews.geocomm.com/community/lists/
>
>
To unsubscribe, write to gislist-unsubscribe@geocomm.com
________________________________________________________________________
Setup a GeoCommunity Account and have access to FAST DataDownloads
and Premium Career Posting at a discounted rate!
https://www.geocomm.com/cgi-bin/accounts/login
On-line Archives available at
http://spatialnews.geocomm.com/community/lists/
|
|
Sponsored by:
For information
regarding
advertising rates
Click Here!
|
