[Proj] Default datum transformation behavior

Brendan Billingsley billinb at nsidc.org
Tue Nov 25 18:12:15 EST 2008

The last question in the PROJ.4 FAQ explains how to use the
+nadgrids=@null argument to prevent a datum shift when doing a
conversion between projections with different projection spheroids.  I
have been using this trick and telling others about this trick.  However
I recently started using a newer version of FWTools and realized that
leaving out the "+nadgrids=@null +wktext" produced the same results as
having it in.  I then grabbed the newest version of proj (4.6.1),
compiled it and confirmed that the behavior has changed.  In my old
version (4.5.0) if I use cs2cs then to prevent the datum transformation
for my conversion I need the +nadgrids=@null argument, but for the new
version I can leave that argument off and I will get the same results as
having the argument on and using the 4.5.0 version.

So has the default behavior been changed, am I missing something or is
this a bug?  If the default behavior has been changed then that is great


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