Date: Wed, 04 May 94 15:48:13 +0200
From: Ralf Kunkel <STE077@ZAM001.ZAM.KFA-JUELICH.DE>
Organization: Forschungszentrum Juelich GmbH
Subject: importing raster maps
To: Office of GRASS integration <grassu-list@max.cecer.army.mil>There are a couple of raster maps I want to import into GRASS 4.1.3. These
maps are referred to a Gauss-Krueger Projection (central meridian 9.0 degrees
east, speroid=bessel) with equidistant spacing in N-S and W-E directions in
this projection.
As far as I could get out of the GRASS-manuals, importing ASCII-data using
r.in.ascii or r.in.ll uses an equidistant spacing of lat-lon coordinates.
Although I dont't know exactly how to arrange this, it should be possible to
convert the GK coordinates of each single raster cell or it's boundaries into
lat-lon coordinates with PROJ. But then, the geographic locations of the
cells should be changed significantly when importing into GRASS.
Right now, I'm stucked on this problem. I wonder if somebody can give me some
hints in importing the data into GRASS.Thanks in advance
Ralf Kunkel
A couple of partial answers.
First: Gauss-Krueger is synonymous with Transverse Mercator. The former
nomenclature is more common in Europe and the latter in North America.
Second: the central meridian of 9 degrees makes it similar to UTM.
BUT do not use UTM unless you determine that a scale factor of
0.9996 (k_0) was spec'ed for the CM.
Regardless, you are going to need the CM scale factor. If you can't
determine what it is you're going to have to guess 1.0.
Third: check the datas easting to see if the zone was prepended as
N,000,000 meters. That is, the easting will have a number larger
than about 800,000m (probably in the range of 2,000,000+).
Knowing these factors, getting the data into GRASS ought to be possible.
Gerald (Jerry) I. Evenden Internet: gie@charon.er.usgs.gov
voice: (508)563-6766 Postal: P.O. Box 1027
fax: (508)457-2310 N.Falmouth, MA 02556-1027