[Proj] RSO, +gamma and Hotine Oblique Mercator Variant A

[Hilmy Hashim]

Mikael,


In http://trac.osgeo.org/proj/ticket/104, you said

A +no_uoff ("no u-offset") means that the origin is at the so-called natural
origin, on the central oblique line of the projection, and near the ordinary
equator (on the "aposphere equator", but I've never understood what an
aposphere is).
>From my simplistic understanding of Hotine's method, during the first part
of the forward projection, the coordinates from the ellipsoid are projected
onto a sphere of "constant total curvature" or an aposphere. I suppose this
makes the maths simpler? So the equator on this aposphere is slightly offset
from the equator on the ellipsoid.

Regards

*Hilmy*
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