[GRASSLIST:2112] understanding r.proj
Len Coop
coopl at ippc2.orst.edu
Tue Jul 17 20:52:17 EDT 2001
I am having problems understanding and using
r.proj,
working in the case of converting from Albers Equal Area (source) into
lat long (target) for version 4.3?
Should I forget trying to use it and upgrade to 5.0?
As I pick apart the shell script (that is r.proj), it seems it expects
me to want to go from
one projection to another via lat long. I want to end up in lat long.
The process used by r.proj seems to be (skipping steps involved in
preparing headers and switching locations):
1) use r.stats to sample an example target map to obtain a site list at
the right resolution and boundaries
?it just grabs the 1st file in the cell directory! - should be able
to specify which one
2) use proj (PROJ.4) to convert site list to source projection (or just
copy file if ll is target projection)
?should it not be using invproj (proj +inv) to convert to ll
3) use proj (PROJ.4) again to convert the ll site list to a site list in
the source projection
(or just copy if ll is the source projection)
4) use s.sample to sample the source map using the converted site list
?why does this work with the next step since we are in the source
projection
5) r.in.ascii to make the new target map
The general process that I think I should be doing is :
1) use r.stats to sample a target map to obtain a site list at the right
resolution and boundaries
2) use proj (PROJ.4) to convert samples to source projection (for my
needs, ll to aea)
3x) no need to use proj a second time now in my case (but would for the
general case)
4) use s.sample to sample the source map using the converted site list
5) use invproj (proj +inv for ll) to convert the samples + data to the
target projection
6) use r.in.ascii to make the new target map
I have not succeeded with either strategy so far.
Are some of my problems because r.proj (GRASS 4.3) expects PROJ 3 rather
than 4?
Thanks for any insights,
Len
--
Leonard Coop
Research Associate
Entomology Dept & Integrated Plant Protection Center
2046 Cordley
Oregon State University
Corvallis OR 97331-2907
Phone 541-737-5523
Fax 541-737-3080
http://osu.orst.edu/dept/entomology/coopl
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