Function:     SKYPRO

Purpose:      Transformation between sky and grid coordinates.

File:         skypro.c

Author:       K.G. Begeman

Use:          INTEGER SKYPRO ( 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
                               SKYSYS ,    Input    integer
                               SKYBASE,    Input    integer
                               PROBASE,    Input    integer
                               MODE   )    Input    integer
              
              SKYPRO   0: transformation successful
                       1: unknown projection
                       2: unknown mode
                       3: CROTA2 = 90.0 for mode 1 and 2
                       4: CDELT1 or CDELT2 equal to zero
                       5: input sky system unknown
                       6: output sky system unknown
                       7: input and output sky system unknown
              XIN      Input X coordinate in degrees or grids.
              YIN      Input Y coordinate in degrees or grids.
              XOUT     Output X coordinate in degrees or grids.
              YOUT     Output Y coordinate in degrees or grids.
              CRVAL1   Projection centre of X coordinate in degrees.
              CRVAL2   Projection centre of Y coordinate in degrees.
              CDELT1   Grid separation along X axis in degrees.
              CDELT2   Grid separation along Y axis in degrees.
              CROTA2   Rotation angle in degrees.
              SKYSYS   Sky system of sky coordinates.
                       SKYSYS          sky system
                         1             equatorial (1950.0)
                         2             galactic
                         3             ecliptic
                         4             supergalactic
              SKYBASE  Sky system of projection centre.
                       SKYBASE         sky system
                         1             equatorial (1950.0)
                         2             galactic
                         3             ecliptic
                         4             supergalactic
              PROBASE  Projection system onto which the sky coordinates
                       are projected:
                       PROBASE         projection type
                         1             AITOFF equal area
                         2             Equivalent Cylindrical
                         3             Flat
                         4             Gnomonic
                         5             Orthographic
                         6             Rectangular
                         7             Global Sinusoidal
                         8             North Celestial Pole
                         9             Stereographic
                        10             Mercator
              MODE     Mode determines what type of input/output
                       coordinates are given/wanted.
                       MODE       XIN     YIN   XOUT   YOUT
                         0        sky     sky   grid   grid
                         1       grid     sky    sky   grid
                         2        sky    grid   grid    sky
                         3       grid    grid    sky    sky

Updates:      Dec 15, 1989: KGB, Document created.