[PROJ] general use of proj_factors

[Thomas Knudsen]

>  If I use something defined with proj_create_crs_to_crs I get incorrect
values for the meridian convergence

Which is as expected: proj_create_crs_to_crs returns a transformation
BETWEEN two CRS. The geometrical factors are meaningfully defined
for projections only. A transformation between two CRS is not in general
a projection.

You may get some numbers out of calling proj_factors with a transformation
as an argument, but you should not expect any kind of meaningful result.

Also, you may get numbers out of a PJ generated from a CRS (EPSG:nnnn),
by ignoring the reference frame information implied, in which case an
eventual projection remains. But if the CRS is, say, geographical or
geocentric cartesian, the factors are meaningless.

**It's apples and pears**. Don't expect meaningful proj_factors from
anything
other than a traditional projection specification.
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