ENPAPS ( surf, coords, u, v, ifail )
====================================

  Find parameters of point on surface

    Can be called from the GO.

Receives:
  KI_tag_surface           *surf           --- surface
  KI_vec_position           coords         --- coordinates of point on surface

Returns:
  KI_dbl                   *u              --- u parameter of 'coords'
  KI_dbl                   *v              --- v parameter of 'coords'
  KI_cod_error             *ifail          --- failure code

Specific errors:
  KI_not_on_surface         point is not on the surface
                            point lies outside the valid parameter range
  KI_invalid_geometry       the surface fails to pass checks
                            surface not supported

Description:

  Returns the parameters of the given point, provided that it lies on the
  given surface. The parameters will lie in the range given in ENSUPA for
  this surface. At parametric singularities, such as sphere poles, the
  non-degenerate parameter is returned as the lowest value in its range.
  The function works for any surface type.

  The surface must be capable of passing the checks imposed by CHCKEN.
  The self intersection check is only performed if the appropriate option is set
  (see SEINTP).