projection problems

[Stefan Jaeger]

Hello,

I have worked several months with an x,y projection in 4.0. I had to do this
because 4.0 did not support the transverse mercator projection in which
I had my data. Now I wanted to use v.proj to get maps in lat/lon 
and digitized in arc/info into my location. I created a new location with ll
where I put the vector maps. I created another one with tmerc projection and 
started v.proj. The idea was to copy those files under my old location with 
the x,y, projection. The conversion went wrong. The programm said south is 
smaller than north or somethimg similar. The problem was that I cannot set
the false easting value, i.e. the constant to add to the calculated 
projected coordinates to avoid negative eastings. We use in Germany the 
Gauss-Krueger projecion which is just a synonym for tmerc and all my 
other maps have region boundaries with Gauss-Krueger values.  I tried the 
projection programm in arc/info as well. I set the spheroid correctly. 
Arc/info has the possibility to add a false easting value to the projected 
coordinates. The result of this conversion was, that the projected easting
coordinates were shifted approx. 300m (!!) too far (northings were +- 
corect).  I checked the results 
with the proj4.1 programm which was absolutely correct. Here are my 
questions:

1. Has anybody made similar experiences with v.proj. or with arc/info? 
2. Is it possible to tell GRASS that all my x,y, maps are actually in 
tmerc projection?

Any hints appreciated.


Stefan Jaeger
Dept. of Geogr.
University of Heidelberg, Germany