Geometry/halfspace_normal_triangle_int_3d.f90 at master · lguez/Geometry · GitHub

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subroutine halfspace_normal_triangle_int_3d ( pp, normal, t, int_num, pint )

!*****************************************************************************80
!
!! HALFSPACE_NORMAL_TRIANGLE_INT_3D: intersection ( norm halfspace, triangle ).
!
!  Discussion:
!
!    The normal form of a halfspace in 3D may be described as the set
!    of points P on or "above" a plane described in normal form:
!
!      PP is a point on the plane,
!      NORMAL is the unit normal vector, pointing "out" of the
!      halfspace.
!
!    The triangle is specified by listing its three vertices.
!
!    The intersection may be described by the number of vertices of the
!    triangle that are included in the halfspace, and by the location of
!    points between vertices that separate a side of the triangle into
!    an included part and an unincluded part.
!
!    0 vertices, 0 separators    (no intersection)
!    1 vertex, 0 separators      (point intersection)
!    2 vertices, 0 separators    (line intersection)
!    3 vertices, 0 separators    (triangle intersection)
!
!    1 vertex, 2 separators,     (intersection is a triangle)
!    2 vertices, 2 separators,   (intersection is a quadrilateral).
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license.
!
!  Modified:
!
!    06 May 2005
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, double precision PP(3), a point on the bounding plane
!    that defines the halfspace.
!
!    Input, double precision NORMAL(3), the components of the normal vector
!    to the bounding plane that defines the halfspace.  By convention, the
!    normal vector points "outwards" from the halfspace.
!
!    Input, double precision T(3,3), the vertices of the triangle.
!
!    Output, integer INT_NUM, the number of intersection points
!    returned, which will always be between 0 and 4.
!
!    Output, double precision PINT(3,4), the coordinates of the INT_NUM
!    intersection points.  The points will lie in sequence on the triangle.
!    Some points will be vertices, and some may be separators.
!
  implicit none

  integer, parameter :: dim_num = 3

  double precision d
  double precision dist1
  double precision dist2
  double precision dist3
  double precision normal(dim_num)
  integer int_num
  double precision pp(dim_num)
  double precision pint(dim_num,4)
  double precision t(dim_num,3)
!
!  Compute the signed distances between the vertices and the plane.
!
  d = - dot_product ( normal(1:dim_num), pp(1:dim_num) )
!
!  Compute the signed distances between the vertices and the plane.
!
  dist1 = d + dot_product ( normal(1:dim_num), t(1:dim_num,1) )
  dist2 = d + dot_product ( normal(1:dim_num), t(1:dim_num,2) )
  dist3 = d + dot_product ( normal(1:dim_num), t(1:dim_num,3) )
!
!  Now we can find the intersections.
!
  call halfspace_triangle_int_3d ( dist1, dist2, dist3, t, int_num, pint )

  return
end