PostGIS  2.5.0dev-r@@SVN_REVISION@@
 void unit_normal ( const POINT3D * P1, const POINT3D * P2, POINT3D * normal )

Calculates the unit normal to two vectors, trying to avoid problems with over-narrow or over-wide cases.

Definition at line 506 of file lwgeodetic.c.

References cross_product(), dot_product(), normalize(), vector_difference(), and vector_sum().

507 {
508  double p_dot = dot_product(P1, P2);
509  POINT3D P3;
510
511  /* If edge is really large, calculate a narrower equivalent angle A1/A3. */
512  if ( p_dot < 0 )
513  {
514  vector_sum(P1, P2, &P3);
515  normalize(&P3);
516  }
517  /* If edge is narrow, calculate a wider equivalent angle A1/A3. */
518  else if ( p_dot > 0.95 )
519  {
520  vector_difference(P2, P1, &P3);
521  normalize(&P3);
522  }
523  /* Just keep the current angle in A1/A3. */
524  else
525  {
526  P3 = *P2;
527  }
528
529  /* Normals to the A-plane and B-plane */
530  cross_product(P1, &P3, normal);
531  normalize(normal);
532 }
void normalize(POINT3D *p)
Normalize to a unit vector.
Definition: lwgeodetic.c:580
static double dot_product(const POINT3D *p1, const POINT3D *p2)
Convert cartesion coordinates on unit sphere to lon/lat coordinates static void cart2ll(const POINT3D...
Definition: lwgeodetic.c:411
static void vector_difference(const POINT3D *a, const POINT3D *b, POINT3D *n)
Calculate the difference of two vectors.
Definition: lwgeodetic.c:441
void vector_sum(const POINT3D *a, const POINT3D *b, POINT3D *n)
Calculate the sum of two vectors.
Definition: lwgeodetic.c:430
static void cross_product(const POINT3D *a, const POINT3D *b, POINT3D *n)
Calculate the cross product of two vectors.
Definition: lwgeodetic.c:419

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