Transformations
can be done between the following systems 
cartesian x y z vx vy vz spherical rmod theta phi vrad vtheta vphi scattering imp.param imp.angle init.separ v_at_inf theta phi tscattering imp.param imp.angle encount.time. v_at_inf theta phi trueanomaly a e i OMEGA omega f eccanomaly a e i OMEGA omega E meananomaly a e i OMEGA omega M peripassage a e i OMEGA omega T
The final transformation is a combination of only three types of transformation.
Within each class of coordinate systems there is one prototype which has
the same name as the class. To get from A to B, the first transformation
is from A to prototype(A), then from prototype(A) to prototype(B), and
finally from prototype(B) to B. these three transformations are called can,
trans, cast,  respectively. 
  
   ___________     trans     __________________________________________
  |           |------------>|                                          |
  | CARTESIAN |<------------|               TRUEANOMALY                |
  |___________|             |__________________________________________|
       |  A                  c |  A             |  A             |  A
       |  |                  a |  | c           |  |             |  |
       |  |                  s |  | a           |  |             |  |   
       |  |                  t |  | n           |  |             |  |
   ____V__|___            _____V__|___     _____V__|____     ____V__|_____
  
  |           |          |            |   |             |   |             |  
  | SPHERICAL |          | ECCANOMALY |   | MEANANOMALY |   | PERIPASSAGE |
  |___________|          |____________|   |_____________|   |_____________|
~/src/nbody/kepler kep2kep.c
Dec 1987 Created - Piet Hut @ Inst. f. Adv. Study, Princeton, NJ 08540, USA Mar 1991 adapted for NEMO V2 - no local error() and warning() PH/PJT Jun 1991 one more appeasement for GCC PJT May 1992 removed local versions of error(*) and warning() PJT 19-jun-92 fixed all those gcc warnings about local declaration mismatch PJT