[GRASSLIST:1598] Re: r.in.gdal and a GeoTIFF

[Markus Neteler]

On Sat, Oct 25, 2003 at 11:32:37AM +0200, Markus Neteler wrote:
> On Fri, Oct 24, 2003 at 02:27:43PM +0200, Markus Neteler wrote:
> > On Thu, Oct 23, 2003 at 10:51:40AM -0500, Ed Davison wrote:
> > > On Thu, 2003-10-23 at 04:43, Markus Neteler wrote:
> > > 
> > > > Searching around I found this file.
> > > > http://edcftp.cr.usgs.gov/pub/data/nationalatlas/shdrlfi020l.tar.gz
> 
> BTW: The ellipsoid/datum within this data set does NOT match
> the metadata description of the same map. Similar things
> I observed with the geological map: The SHAPE file lacks the .prj
> file, the geological map metadata refer to a third spheroid.
> 

A followup for the record: 
I have been contacting the USGS/National Atlas people, and they 
explained the situation:

Concerning the raster maps:
"The North American Shaded Relief is in a Lambert Azimuthal Equal Area
 projection, on a sphere.  We use the same projection for all our image
 files.
"

"The WGS references that remain in the GeoTIFF are an artifact of Arc.  The
 source data (GTOPO30) was referenced to WGS84.  What I've been told is
 that Arc won't accept blank values for the ellipsoid and datum, and since
 nothing applies for a sphere, the original values are not replaced.
 However, our file really is on a sphere with the parameters supplied in
 our metadata, so the references to WGS84 can be ignored.
"

Concerning the vector maps:
"The Roads layer is distributed in geographic coordinates, as are all our
 vector map layers.  Vectors are distributed in geographics so that our
 users can easily convert to their preferred projection.
 Our geographic files (again, all the vector map layers) use the GRS1980
 spheroid, with a semi-major axis of 6378137.

 If you want to combine our image files with our vector data, the vector
 data needs to be projected to the Lambert Azimuthal Equal Area projection.
"

So the previously posted 'ogr2ogr' command needs a correction ("-a_srs")
to produce a correct result.

Hope this helps,

 Markus