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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | Fwd: Re: GISList: DRGs |
| Date: |
04/17/2003 03:55:01 PM |
| From: |
John D. Evans |
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Hello DuBose,
The DRG images are exactly the same in the new datum! Only their
georeferencing changes.
(Read the fine print in the margins: the datum shift is essentially a
constant over each 7.5-minute area. This is of course an approximation,
valid for the DRG's 2.54m resolution vs. national map accuracy standards, etc.)
So, just use libgeotiff's listgeo and geotifcp
(http://www.remotesensing.org/geotiff/geotiff.html) to adjust the GeoTIFF
tags in each DRG. Use the x,y shifts printed in the DRG margins, or (if
you've got a lot of DRGs) recompute them using PROJ.4
(http://www.remotesensing.org/proj/) or your favorite datum transformer.
We used this approximation to serve up seamless DRGs online at
http://ortho.ftw.nrcs.usda.gov in both NAD27 and NAD83 UTM, using the same
image collection (~100 GB?) with two different index files (~1MB).
- John D. Evans, Ph.D.
Global Science & Technology, Inc. (GST)
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At 03:25 PM 4/16/2003 -0400, DuBose Griffin wrote:
I am trying to acquire drg's of the south carolina coast. Our agency has
these but they are in the NAD 27 datum. I want the DRGs in NAD 83. Do these
exist. I have exhausted the USGS website and I cannot seem to acquire this
information. Has anyone ordered these before and any suggestions are
welcomed.
Thank you
DuBose
** Please Note New Phone and Fax Numbers Below
***********************************************************
Ms. DuBose Griffin
Endangered Species Biologist
GIS Analyst
Sea Turtle Desk
South Carolina Department of Natural Resources
Wildlife and Freshwater Fisheries Division
Wildlife Diversity Section
217 Fort Johnson Road
Post Office Box 12559
Charleston, South Carolina 29422-2559
U.S.A.
Email: griffind@mrd.dnr.state.sc.us
Voice: 843-953-9016
Fax: 843-953-9353
URL: http://water.dnr.state.sc.us/
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