[Proj] WGS84 to Sphere Inconsistency Between Proj Versions
Faron Anslow
fanslow at eos.ubc.ca
Thu Aug 21 19:50:13 EDT 2008
Hello,
This is my first post to the list, so I hope this hasn't been covered
extensively elsewhere (probably has).
A Colleague and I are working with an atmospheric reanalysis product
(NARR) that is on a fairly odd projection. That projection being
lambert conformal conic with a spherical earth with radius of 6371200
m. To assist in projecting site data, DEMs and etc from lat/long WGS84
coords to our spherical projection my colleague has written a matlab
interface to the proj library. Our problem arises when we compare
reprojected coordinate values from cs2cs or GRASS with the matlab mex
file result. For instance, with cs2cs, running:
cs2cs +proj=latlong +datum=WGS84 +to +proj=lcc +lat_1=50 +lat_2=50
+lat_0=50 +lon_0=-107 +a=6371200.0000000000 +es=0.0 +f=0.0 +no_defs -r
on the coordinates 70.933 -8.667 will yield:
2859697.41 4597308.07 0.00
while our matlab mex file gives:
2873633.37 4593659.17 -12148.43
I suspect the problem is that documented in the FAQ, which requires the
addition of +nadgrids=@null to the proj command. However, when I add
this to the cs2cs call, the results don't change. When I add it to the
mex call, the mex file crashes (not set up to handle the @null I
guess). Our question is which result is the correct one? We suspect
that a big change in elevation should be expected when switching from
the WGS84 ellipsoid to the sphere. cs2cs from proj 4.4 installed on
another machine gives results that agree with our mex file.
Even stranger is that when we compile the mex file with the line:
mex Work/Code/Matlab_tools/cs2cs_proj4.c /usr/lib/libproj.a
instead of:
mex -l proj /home/fanslow/Work/Code/Matlab_tools/cs2cs_proj4.c
the matlab result matches that of the cs2cs command given above.
If anyone has any answers, or even if you want to try to project these
test coords using your proj install, and send those along, your help
would be greatly appreciated.
Thanks a ton,
Faron
--
Post Doctoral Researcher
Department of Earth and Ocean Sciences
The University of British Columbia
6339 Stores Road
Vancouver, British Columbia
Canada, V6T 1Z4
604 822 3063
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