SPC (State Plane Coordinates) extension?

[paron]

I'm coding a converter for SPC (State Plane Coordinates) to/from GCS
(lat-lon).

State Plane Coordinates are handy since they come out in ordinary
rectangular feet or meters. In addition, many government agencies in
the U.S. use State Plane for their work. Another similar system is
UTC; it is a fairly simple variation on the SPC conversion.

Would rectangular/angular conversion be a worthwhile extension to
geoRuby, or should it be on its own, or am I the only one that needs
it? Or is it already baked right in, but I missed it?

Ron