Stoneyhurst heliographic coordinate system

Note for ongoing work..

The Stoneyhurst heliographic coordinate system is defined in following article among other sun-based coordinate systems:

THOMPSON, W. T. Coordinate systems for solar image data. Astronomy & Astrophysics, 2006, 449.2: 791-803. Also available at http://secchi.nrl.navy.mil/wiki/uploads/Main/coordinates.pdf

Findings: the term "heliographic latitude/longitude" is parallel to geographic lat/lons.  When we are aware about oblateness of the Earth (i.e. almost everywhere except for weather modellers), we distinguish "geographic" and "geocentric" latitudes.  More general terms are "planetographic" and "planetocentric".  In the Stoneyhurst system, we assume spheric sun (i.e. zero oblateness) implicitly, so we use the term "heliographic" in spite of the mathematical formula based on heliocentric coordinates.