Function:     PROCO

Purpose:      Function which does the conversion of grid to sky
              coordinates and vice versa.

File:         proco.c

Author:       K.G. Begeman

Use:          INTEGER PROCO( XIN   ,     Input      double precision
                             YIN   ,     Input      double precision
                             XOUT  ,     Output     double precision
                             YOUT  ,     Output     double precision
                             CRVAL1,     Input      double precision
                             CRVAL2,     Input      double precision
                             CDELT1,     Input      double precision
                             CDELT2,     Input      double precision
                             CROTA2,     Input      double precision
                             PROSYS,     Input      integer
                             MODE  )     Input      integer

              PROCO    0: successful conversion
                       1: unknown projection
                       2: unknown mode
                       3: CROTA2 = 90.0 for mode 1 and 2
                       4: CDELT1 or CDELT2 equal to zero
                       5: Input or internal values outside range of 
                          this projection
              XIN      Input X coordinate (Longitude in degrees or
                       X grids).
              YIN      Input Y coordinate (Latitude in degrees or
                       Y grids).
              XOU      Output X coordinate (X grids or Longitude
                       in degrees).
              YOU      Output Y coordinates (Y grids or Latitude
                       in degrees).
              CRVAL1   Projection centre longitude (Longitude in
                       degrees).
              CRVAL2   Projection centre latitude (Latitude in
                       degrees).
              CDELT1   X grid separation in degrees.
              CDELT2   Y grid separation in degrees.
              CROTA2   Rotation angle in degrees.
              PROSYS   Type of projection:
                        1    AITOFF equal area projection
                        2    Equivalent Cylindrical projection
                        3    Flat projection
                        4    Gnomonic projection
                        5    Orthographic projection
                        6    Rectangular projection
                        7    Global Sinusoidal projection
                        8    North Celestial Pole projection
                        9    Stereographic projection
                       10    Mercator projection
              MODE     Mode determines what type of input/output
                       coordinates are given/wanted.
                       MODE       XIN     YIN   XOUT   YOUT
                         0        LON     LAT      X      Y
                         1          X     LAT    LON      Y
                         2        LON       Y      X    LAT
                         3          X       Y    LON    LAT

Updates:      Jan  5, 1990: KGB, Document created.
              Sep 09, 1998: VOG, Replaced -180, 180 degrees restriction 
                            for AITOFF and RECTANGULAR (a,y) -> (x,d)
                            projections by 0, 360 restriction.
              Jan 24, 2007: Changed post condition for aitoff