Notes on Gravity
(From email 7 September, 2012)
In the gravity folder there is a routine called Sgrav. It makes a file called SGRAV.TXT that is like SHAPE.TXT but with extra columns for surface acceleration, potential and laplacian (just as a check). This is for a non-rotating body with GM=1. Then Sacc, Spot, Sslp and Selv compute the surface acceleration, potential, slope and elevation (above geoid) for the body with the correct GM and omega. Selv also makes the geoid file.
The main subroutine is GRAVITY. It computes the gravity at any point in space, inside, outside or on the surface. I used it in my trajectory integration program for landing on Eros. GLATLON is a special program I wrote for someone who wanted various information for points on Eros. You can see how GRAVITY is used there. There are five subroutines called by gravity called D1-D5 that subdivide the surface elements if your point of interest is too near to a facet. Essentially it mimics a recursive call since you can't do that in FORTRAN.