[Proj] apply plane rotation after transverse Mercator projection

[Duffy, Garret]

Hi,

I would like to design a projection that is similar to a TM projection
except append the parameter "XY_Plane_Rotation", i.e. rotate the XY
axes.  Is this possible to do in PROJ4?  I note the tmerc doesn't have
an alpha parameter or similar.  I already tried using RSO but it's
overkill for what I want to do, all I want to do is apply a simple
cartesian rotation to the projected XY axes.

Another thing I tried was editing a PRJ file for a TM projected data and
then appending "PARAMETER["XY_Plane_Rotation",XX]" to the file but that
doesn't seem to work.

Do I have to define a custom PROJCS that is based on tmerc but allows
for the XY_Plane_Rotation parameter?

Any suggestions gratefully would be (very) gratefully received as I have
been trying to do this supposedly simple thing all week.

Regards,

Garret
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