ENPAPC ( curve, coords, t, ifail )
==================================

  Find parameter of point on curve

    Can be called from the GO.

Receives:
  KI_tag_curve             *curve          --- curve
  KI_vec_position           coords         --- coordinates of point on curve

Returns:
  KI_dbl                   *t              --- parameter of 'coords'
  KI_cod_error             *ifail          --- failure code

Specific errors:
  KI_not_on_curve           the supplied point is not on the curve
  KI_invalid_geometry       the curve fails to pass checks
                            curve not supported

Description:

  Returns the parameter of the given point, provided that it lies on the given
  curve. The parameter will lie in the range given by ENCUPA.

  The curve 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).