Geometry of the Observed Solar Surface
1. Use soho_ephem.c to determine L0, B0 as viewed by SOHO-MDI at a particular time like this, with year.month.day_hour:minute:second
STANFORD> soho_ephem 2002.04.14_22:52:56which will return
OBS_DIST (au L0 (deg B0 (deg VR (m/s) VN (m/s) VW (m/s) Carr Rot 0.9919838074 150.007 -5.6812 476.97 2363.58 29524.2 1988.5833
Note: If fastrack.c left the MDI header keywords OBS_L0 and OBS_B0 in the fastracked cube headers, the need for soho_ephem would be redundant.
The solar ephemeris can also be calculated from this tool.
To calculate the longitude and latitude of each spatial point of a map which has been Postel projected use geom_postel.pro.
A solar rotation applet good to understand L0 and B0.