INCUFA ( cu, bound, face, intpts, cuparm, suparm, incods, topol, nintpt,
=========================================================================
ifail )
=======
Intersect curve and face
Receives:
KI_tag_curve *cu --- curve
KI_vec_position bound[2] --- start and end of curve
KI_tag_face *face --- face
Returns:
<KI_tag_list_dbl> *intpts --- points of intersection
<KI_tag_list_dbl> *cuparm --- curve parameters at ints.
<KI_tag_list_dbl> *suparm --- surface parameters at ints.
<KI_tag_list_int> *incods --- tokens describing intersections
<KI_tag_list_<entity>> *topol --- entity intersected
<KI_int_nitems> *nintpt --- number of points returned
KI_cod_error *ifail --- failure indicator
Specific errors:
KI_cant_do_intersect cant perform requested intersection
cant do intersect
KI_invalid_geometry curve fails checks
KI_not_on_curve start or end point not on curve
KI_bad_end_points curve not defined between start and end points
KI_missing_geom face lacks geometry
Description:
INCUFA finds the intersections between a bounded curve and a face. It returns
a list of intersection coordinates and a list of tokens classifying the
intersections. If the bounded curve passes through an edge or vertex of the
face the tag of the appropriate entity is also returned. If the bounded
curve does not intersect the face, no tag information is returned, but is
deemed to be a successful operation.
The intersections are ordered along the bounded curve, and are classified
according to the direction of the curve.
The interval of the curve to be intersected with the face is specified
by giving the start and end coordinates. These are given in the array 'bound',
in the order start and then end. If these points are the same, and the
geometry of the curve is closed, the complete curve will be used and the end
points will not be treated specially below - i.e. information as to whether
they lie in or on the face will not be returned as this is merely a method of
specifying the whole curve.
If the curve is a trimmed curve the supplied bounds are ignored. However valid
vectors should be supplied.
The intersection coordinates are returned in a list of length 3*'nintpt'; if
there are no intersections of the curve and face within the interval of
the curve bounded by 'bound', 'nintpt' is returned as zero and 'intpts' is
returned as the NULTAG. If 'nintpt' intersections are found the list
'cuparm' contains 'nintpt' corresponding curve parameters and 'suparm'
contains the corresponding u,v pairs of surface parameters. The curve
and surface parametrisations are defined in the documentation of ENCUPA
and ENSUPA.
Any edges or vertices intersected by the curve are returned in a list
('topol') of length 'nintpt'.
The intersection types are returned in a list ('incods') of length 'nintpt'.
There are two codes for points of intersection when the curve and the surface
of the face intersect in a single point and eleven codes for intersections
where all or part of the curve lies in the surface.
Single point intersections between bounded curve and surface of face:
Code | Possible entry | Description
| in 'topol' |
_______|__________________|____________________________________________
CFCLSI | Edge or Vertex | The curve passes through the surface of the
| or NULTAG | face.
CFCLTG | Edge or Vertex | The curve touches the surface of the face
| or NULTAG | but does not pass through the surface.
Intersections with the bounded curve lying in the surface of the face:
Code | Possible entry | Description
| in 'topol' |
_______|__________________|____________________________________________
CFCLEF | Edge or Vertex | The curve passes from being outside
| | the face to being in its interior.
CFCLLF | Edge or Vertex | The curve passes from being in the interior
| | of the face to being outside the face.
CFCLEB | Vertex | The curve passes from being outside the
| | face to a region of coincidence with its
| | boundary.
CFCLLB | Vertex | The curve passes from a region of
| | coincidence with the boundary of the face
| | to being outside the face.
CFCLEI | Vertex | The curve passes from a region of
| | coincidence with the boundary of the face
| | to being in the interior of the face.
CFCLLI | Vertex | The curve passes from being in the interior
| | of the face to a region of coincidence with
| | the boundary of the face.
CFCLTI | Edge or Vertex | The curve is tangent to the inside of an
| | edge or passes through a vertex but remains
| | inside the face.
CFCLTO | Edge or Vertex | The curve is tangent to the outside of an
| | edge or passes through a vertex but remains
| | outside the face.
CFCLUC | Edge or Vertex | The start or end of the curve is inside
| or NULTAG | the face or lies on its boundary.
CFCLSC | Edge or Vertex | The curve enters the face at the start of a
| or NULTAG | region of coincidence with the surface.
CFCLEC | Edge or Vertex | The curve leaves the face at the end of a
| or NULTAG | region of coincidence with the surface.
Whether the curve enters or leaves the face is determined by the direction
of the curve, 'cu'.
Any B-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).
