OUCOCU ( curve, start, end, ctol, atol, stol, posns, npos, ifail )
==================================================================

  Output coordinates on curve.

Receives:
  KI_tag_curve             *curve          --- curve to be output
  KI_vec_position           start          --- starts from here
  KI_vec_position           end            --- ends here
  double                   *ctol           --- max permitted chordal error
  double                   *atol           --- max permitted angular error
  double                   *stol           --- max permitted step length

Returns:
 <KI_tag_list_dbl>         *posns          --- list of vector components
  KI_int_nitems            *npos           --- number of items in list
  KI_cod_error             *ifail          --- failure code

Specific errors:
  KI_tolerances_too_tight   failed to meet tolerances
  KI_stol_too_small         invalid step length control set
  KI_atol_too_small         invalid angular control set
  KI_ctol_too_small         invalid chordal control set
  KI_wrong_direction        start and end in wrong order
  KI_coincident             start and end coincide but curve not closed
  KI_not_on_curve           coords not within resolution distance of curve

Description:

  This routine outputs coordinates along 'curve' from 'start' to 'end'.
  The user may specify the controls that govern the output of the
  coordinates or request that coordinates be output to default controls.

  To help explain the meaning of 'ctol', 'atol', and 'stol', a chord is
  defined to be the straight line between adjacent coordinates. A step is
  the process of progressing from one location to the next.

  'ctol' is the max permitted chordal error. That is the maximum permitted
         distance from a chord to the curve between the ends of the chord.

  'atol' is the max permitted angular error. It is the maximum permitted
         sum of the angles between the chord and the tangents to the curve
         at the ends of the chord.

  'stol' is the max permitted chordal length.

  'ctol', 'atol', and 'stol' are independent means of controlling the
  output of the points. There will be no step where a valid 'ctol',
  'atol', or 'stol' limit is exceeded. There is no guarantee that 'ctol',
  'atol' or 'stol' will actually be attained.

  There are lower limits to the values of 'ctol', 'atol' and 'stol' that
  can be used as controls. These values are not specified here as they
  depend upon the model resolution. Where these limits are exceeded
  suitable failure codes are returned.

  If all the controls are set to <= 0.0, default controls are applied
  which capture the shape of the curve. Where some of the controls are set
  to <= 0.0, those controls that are <= 0.0 are ignored and coordinates
  are output to the remaining valid controls.

  The positions stepped to are returned in 'posns', a list of doubles in
  the form

  Xn, Yn, Zn, X(n+1), Y(n+1), Z(n+1), X(n+2) ......

  where n varies from 0 to 'npos'/3 - 1.

  X0,Y0,Z0 is 'start' first location stepped to and
  XL,YL,ZL is 'end'   last location  stepped to.
        where L = 'npos'/3 - 1

  'start' to 'end' must follow the natural direction of the curve as indicated in
  the appropriate KI curve creation routine. If the curve is a trimmed curve the
  bounds are ignored. However valid vectors should be supplied.