ENPOPC ( curve, t, ndrvs, p, ifail )
====================================

  Evaluate point from curve parameter

    Can be called from the GO.

Receives:
  KI_tag_curve             *curve          --- curve
  KI_dbl                   *t              --- parameter of required point
 <KI_int_nitems>           *ndrvs          --- number of derivatives required

Returns:
  KI_vec_derivatives        p[ndrvs+1]     --- point and derivatives
  KI_cod_error             *ifail          --- failure code

Specific errors:
  KI_bad_parameter          parameter out of range
  KI_too_many_derivatives   too many derivatives requested
  KI_invalid_geometry       curve not supported

Description:
  Calculates the Cartesian coordinates of the point at the given parameter
  value 't', and also the derivatives with respect to 't', up to order
  'ndrvs'.

  Except for B-curves, which can be evaluated out of range, if ENCUPA indicates
  that this curve is not periodic or infinite, then the parameter 't' must be in
  the range specified in ENCUPA for this curve.

  Where derivative discontinuities exist at a junction between segments, the
  derivatives just after the discontinuity are returned.

  For all curve types other than B-curves only derivatives up to and including
  second order may be requested.

  In the case of foreign geometry curves (type TYCUFG), the maximum
  number of derivatives that can be returned by this function is determined
  by the curve's external evaluator. The evaluator should, at least, be
  able to calculate up to second order derivatives.

  In the case of constant-parameter-line curves (type TYCUCP), the maximum
  number of derivatives that can be returned by this function would depend
  on the evaluators for the underlying surface geometry.