Adding isea to proj4

make PJ_isea.c
cp PJ_isea.c path/to/proj-4.7.0
cd path/to/proj-4.7.0
patch -p1 < ../isea/proj4.patch              

now build proj.4 as usual for your system

-- postgis

There is too much numerical instability to try to project directly with postgis.
The interruptions make it almost impossible to reconstitute the input polygons.

Might be able to do it by computing segments, and then ordering the segments
in crossing order.


ISEA Params

Aperture will set the scaling property

Resolution is either the resolution level for the given aperture,
or the total number of hexes along a triangle side if aperture is zero.

I think the ISEA plane projection is offsetting to avoid negative Y coords.