projecting problems

GRASS GRASS user
1

Hello GRASS community...

I've been trying to project data from a LAEA site with a
central meridian of 180W to a LAEA locations with a cental
meridian of 0 E (basically turning data in the"same projection
" 180 degrees".

-results-
r.proj works occationally but the depending on how the data
         has been cut it either gives the error that north must be
         greater than south or then it projects a small piece of the
         wanted area leaving the rest blank.

v.proj doesn't give any errors and everything seem ok until
         data is looked at. Then it may be noticed that the vectors
          have been turned around to the right direction but are
          somehow placed having their south edge starting from
          where the north limit is supposed to be

Similar trouble is met when the data is tried to be spooled though
a LatLong locations - where data is projected but not to the correct
geographical location.

But then there is no trouble projecting material from Latlong to either
of the above mentioned locations (laea180 anf laea0)

Any suggestions?
Is it a problem with the projecting program or could there be a
simpler answer?

thanks in advance...
Juhana
-----------------------------------------------------------------
Juhana Nieminen, Division of Environmental Biology, GIS Laboratory
P.O.Box 44 (Jyrangontie 2) tel: +358-9-191 40059
FIN-00014 University of Helsinki fax: +358-9-191 40048
Finland http://ginkgo.pc.helsinki.fi
-------------------------------------------------------------------

2

On Sat, 6 Nov 1999, juhana wrote:

r.proj works occationally but the depending on how the data
         has been cut it either gives the error that north must be
         greater than south or then it projects a small piece of the
         wanted area leaving the rest blank.

v.proj doesn't give any errors and everything seem ok until
         data is looked at. Then it may be noticed that the vectors
          have been turned around to the right direction but are
          somehow placed having their south edge starting from
          where the north limit is supposed to be

Any suggestions?
Is it a problem with the projecting program or could there be a
simpler answer?

It's a problem with r.proj and v.proj. The programs were not designed
to handle other than cylindrical projections and have to be rewritten to
be able to handle the other types. r.proj needs more extensive changes
than v.proj. You may get around the wraparound problem in v.proj by
avoiding to define a full -180-180 region. Leave one of the egdes just one
snap (one resolution unit) below the full value.

Morten Hulden