[Proj] Help with use of swisstopo NTv2 grid shift ?
strk at keybit.net
Mon Jan 23 11:44:40 EST 2012
I'm trying to understand how to use the swisstopo grid shift
CHENYX06a.gsb file and would like to ask if anyone of you used
Following instructions found on this message:
I've prepared a couple of definitions pretending that the target
(CH1903+) was a WGS84 and defined the input (CH1903) as needing
the CHENYX06a.gsb gridshift:
+proj=longlat +ellps=WGS84 +nadgrids=CHENYX06a.gsb +no_defs
+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs
But when trying to convert, proj4 reports that the gridshift file is only
valid within the following range of coordinates:
NTv2 CHENyx06 661x313: LL=(5.55,45.4666667) UR=(11.05,48.0666667)
pj_apply_gridshift(): failed to find a grid shift table for
This surprised me as the .asc version of the gridshift seems to
contain a different range:
Which matches the CH1903 and CH1903+ coordinate systems, being supposedly
Is it possible that the .gsb file is different from the .asc file ?
Or where does proj4 get the LL/UR data from ?
Any help with using CHENYX06a.gsb with proj4 is appreciated,
Thanks in advance.
() Free GIS & Flash consultant/developer
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