[Proj] Grid shift files.

[Roger Oberholtzer]

I am trying to use a grid shift file via the C API.

It works for me in one situation, but not another:

The working one (OSTN02):

                +proj=tmerc
                +lat_0=49
                +lon_0=-2
                +k=0.9996012717
                +x_0=400000
                +y_0=-100000
                +ellps=airy
                +nadgrids=gb.gsb
                +units=m
                +no_defs

The one that is not working (RD New):

                +proj=sterea
                +lat_0=52.15616055555555
                +lon_0=5.38763888888889
                +k=0.9999079
                +x_0=155000
                +y_0=463000
                +ellps=bessel
                +nadgrids=rdtrans2008.gsb
                +units=m
                +no_defs

The grid shift files are in the same directory. The strange thing is that
when I trace the program execution (strace on Linux), I see that the OSTN02
file gb.gsb is opened and read. However, the one that is not working (RD
New) does not even try to open the rdtrans2008.gsb file. So it is not a
matter of the format of the file. It is not even being accessed. (I may
later have a file format issue. I hope not.)

I know it's old, but this is with 4.8.0. I cannot think the mechanics of
opening the file are different. Could it be related to another parameter I
am using in RD New? +proj or +ellps?

-- 
Roger Oberholtzer
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