[Proj] Rectified Skew Orthomorphic projection, again...

Carl Godkin cgodkin at gmail.com
Wed Dec 16 00:27:32 EST 2009


Almost 6 years ago I asked a question on this list (actually, a predecessor
list) about the rectified skew orthomorphic projection as used in Malaysia.


I offered a patch which ended up as Bugzilla 461 to provide an alternative
"omerc" called "rso" since the former was almost but not quite correct for
batches of test points I had.

At the time Frank said he'd wait for Gerald to weigh in on the situation
which he did (as you could see from the email thread).  Gerald succeeded
to producing the correct results by adding another parameter (which he
"gamma_c") to "omerc."

I had meanwhile patched our copy of PROJ 4.4.7 (as I explained in the
Bugzilla entry) so I was happy.

Here's where I made my mistake:

When we updated PROJ versions, I assumed that Gerald's change was
in the PROJ code.  I didn't realized that Gerald had apparently only made
the change to support "gamma_c" (thus obviating my patch) to his libproj
version, and not to PROJ.  (Until today when I started noticing the
message about "gamma_c" not being used, I was unaware of this!)

What should I do?  For now, I've just re-applied my old patch to a more
recent version of PROJ and I'm getting the correct results again.  I
guess the right thing to do would be to patch the "omerc" code as
Gerald did, but I don't know how to do that and his code doesn't seem
to be available anywhere any longer.

Thanks for listening,

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