[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
news.
Thanks,
Brendan
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