Using the orthographic projection +proj=ortho fails if not explicitly setting +x_0=0 +y_0=0 despite that the proj docs for this state both should already default to 0.0.

This seems like a bug, that the defaults are not getting applied, contrary to docs.

This is undesirable for usability, as the user cannot anticipate which parameters they are required to set (except by trial and error, or searching for usage examples from elsewhere to compare).

For example, +proj=ortho +lat_0=-23.117 +lon_0=132.133 +x_0=0 +y_0=0 +a=6370997 +b=6370997 +units=m works fine, but a bare +proj=ortho does not.

Originally posted by @benjimin in #99