Method IntersectWithLine

Common/DataModel/vtkPlane.cxx:271–330

------------------------------------------------------------------------------ Given a line defined by the two points p1,p2; and a plane defined by the normal n and point p0, compute an intersection. The parametric coordinate along the line is returned in t, and the coordinates of intersection are returned in x. A zero is returned if the plane and line do not intersect between (0<=t<=1). If the pl

// do not intersect between (0<=t<=1). If the plane and line are parallel,
// zero is returned and t is set to VTK_LARGE_DOUBLE.
int vtkPlane::IntersectWithLine(
  const double p1[3], const double p2[3], double n[3], double p0[3], double& t, double x[3])
{
  double num, den, p21[3];
  double fabsden, fabstolerance;

  // Compute line vector
  //
  p21[0] = p2[0] - p1[0];
  p21[1] = p2[1] - p1[1];
  p21[2] = p2[2] - p1[2];

  // Compute denominator.  If ~0, line and plane are parallel.
  //
  num = vtkMath::Dot(n, p0) - (n[0] * p1[0] + n[1] * p1[1] + n[2] * p1[2]);
  den = n[0] * p21[0] + n[1] * p21[1] + n[2] * p21[2];
  //
  // If denominator with respect to numerator is "zero", then the line and
  // plane are considered parallel.
  //

  // trying to avoid an expensive call to fabs()
  if (den < 0.0)
  {
    fabsden = -den;
  }
  else
  {
    fabsden = den;
  }
  if (num < 0.0)
  {
    fabstolerance = -num * VTK_PLANE_TOL;
  }
  else
  {
    fabstolerance = num * VTK_PLANE_TOL;
  }
  if (fabsden <= fabstolerance)
  {
    t = VTK_DOUBLE_MAX;
    return 0;
  }

  // valid intersection
  t = num / den;

  x[0] = p1[0] + t * p21[0];
  x[1] = p1[1] + t * p21[1];
  x[2] = p1[2] + t * p21[2];

  if (t >= 0.0 && t <= 1.0)
  {
    return 1;
  }
  else
  {
    return 0;