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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | Re: GISList: Hawaii GIS |
| Date: |
08/01/2002 04:03:35 PM |
| From: |
Laurence R Moore |
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Thomas Harris wrote:
> 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?
Mike Flannigan:
>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.
There are 127 7.5-minute quads in Hawaii. Many have been revised in the
last few years: DRGs of 86 revised quads have been published at this
writing.
The original maps have some exceptionally confusing characteristics. They
are projected on the Old Hawaiian Datum, the UTM grids are on a different
spheroid than the graticule, and the DRGs use some awful kludges to
reconcile these things with the GeoTIFF standard.
The revised maps are on NAD83, and should be a pretty good fit to other
modern data sources.
So the first question is: which data do you have? The datum listed in the
lower left credit note is the definitive way to tell. The edition date in
the lower right will be 1996 (I think) or later for the new maps, and
(probably) much earlier for the old maps.
----------
Larry Moore
U.S. Geological Survey
Mid-Continent Mapping Center
lmoore@usgs.gov
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