Subroutine:   irco_deproject

Purpose:      Reconstructs celestial sphere from plane projection.

Category:     IRAS

File:         irco_deproject.c

Author:       Fred Lahuis

Use:
       CALL IRCO_DEPROJECT(
                      PRID,     I      integer,
                      X, Y,     I      double precision array(N),
                      XYZ,      O      double precision array(3*N),
                      N)        I      integer.

              PRID    a projection system number (see IRCO_PRNAME),
              X, Y    the coordinates on the plane,
              XYZ     corresponding coordinates on the sphere,       
              N       number of coordinates to be deprojected.      

       This subroutine is the opposite of IRCO_PROJECT.
                                                                      
       See IRCO_PROJECT for common properties of the projection methods.
       Note that at the edge effects may cause loss of accuracy,
       and that maps that are finite (e.g. azimuthal equal-area proj.)
       may behave funny when points beyond the edge are de-projected.

       However, it is guaranteed that any point in the plane will
       be de-projected onto a point of the unit sphere.
       Projections where the formulae lend themselves to a periodic
       representation (e.g.cylindrical) will use this periodicity,
       otherwise points outside the map will be moved to the map edge.

References:   IRCO_PRNAME, IRCO_PROJECT.

Updates:      91 Dec 16 Fred Lahuis,       Creation date

Original:     PRUNPR