[Proj] Programmatically obtaining the domain of a projection

[Phil Elson]

I've got a case where I would like to identify the domain of a projection
programmatically. Take the geos projection for example:


$> invproj +proj=geos +h=35785831 +units=m
5.3e6 0
68d48'11.267"E    0dN

5.4e6 0
74d56'57.772"E    0dN

5.5e6 0
*    *


$> invproj +proj=geos +h=50000000 +units=m
5.5e6 0
69d42'46.646"E    0dN

5.6e6
74d40'19.703"E    0dN

5.7e6
*    *


Are the mathematical limits of Proj4 projections generally available (the C
interface is fine), or is using a numerical method the only way to
calculate the domain?


Notes:
 * There are some domains/bounds available on spatialreference.org (e.g.,
http://spatialreference.org/ref/epsg/4277/) but they are not exhaustive,
are transformed to WGS84 and have presumably been calculated manually.
 * I've had a quick look at PJ_geos to see if this particular example has a
simple solution (and indeed grepped for "limits", "bounds", and "range" in
the whole proj.4 source) without much luck.
 * I've already got a programmatic solution to this, I'm really looking to
find out if there is a more elegant mathematical answer to my problem.

Many thanks in advance,

Phil
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