Which mapproject -Job to get same result as proj?

Q&A
1

Hello. In https://proj.org/en/9.2/operations/projections/omerc.html#usage one sees

$ echo 12 55 | proj +proj=omerc +lon_1=-1 +lat_1=1 +lon_2=0 +lat_2=0
349567.57 6839490.50

Just curious, how can I produce the same results with mapproject? What
should I plug in for the “?” below to arrive at the same answer:

$ echo 12 55 | gmt mapproject -R?/?/?/?+r -Job-1/1/0/0/?c -? -? -?
349567.57 6839490.50

Thanks!

2 
echo 12 55 | gmt mapproject -J"+proj=omerc +lon_1=-1 +lat_1=1 +lon_2=0 +lat_2=0"
349567.574844   6839490.49645

or

echo 12 55 | gmt mapproject -J+proj=omerc+lon_1=-1+lat_1=1+lon_2=0+lat_2=0
349567.574844   6839490.49645

See just above https://docs.generic-mapping-tools.org/dev/gmt.html#the-r-option

3

I see.
I have followed up in Docs: how could `-Jo|O[a|A]` all map to just `-Jomerc`? .

4

Yes, we really must remove those projection aliases from docs (and keep the code for backward compat). They were introduced long ago when creating the GDAL gmt driver. Now that we have a real proj4 implementation they are nothing but a source of confusion.

1 Like
5

Please add to submit agenda so not forgotten.

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