[Proj] How can I get transformation matrix from `invproj`?

Ken Mankoff mankoff at gmail.com
Tue Mar 13 08:00:18 EST 2018

I'm working with data on a rotated pole. I can project from "real world" to
"rotated" coordinates with the following command:

invproj -f "%f" +proj=ob_tran +o_proj=latlon +o_lon_p=-200 +o_lat_p=18
+lon_0=180 -m 57.295779506

I'd like to adjust some GRASS vectors. They aren't simple point vectors so
I can't easily export | invproj | import. However, GRASS does have a
v.transform command https://grass.osgeo.org/grass74/manuals/v.transform.html

I'm having trouble figuring out two things:

1) What is the translation and rotation that occurs based on the invproj
command above
2) How to I convert that information to the x y shift and z rotate expected
by the v.transform command.

I'm hoping this list can help with the first?

Thank you,

  Ken Mankoff
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