PostGIS  2.2.8dev-r@@SVN_REVISION@@

◆ unit_normal()

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 491 of file lwgeodetic.c.

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

Referenced by clairaut_cartesian(), edge_calculate_gbox(), edge_intersection(), edge_intersects(), test_sphere_project(), and vector_rotate().

492 {
493  double p_dot = dot_product(P1, P2);
494  POINT3D P3;
495 
496  /* If edge is really large, calculate a narrower equivalent angle A1/A3. */
497  if ( p_dot < 0 )
498  {
499  vector_sum(P1, P2, &P3);
500  normalize(&P3);
501  }
502  /* If edge is narrow, calculate a wider equivalent angle A1/A3. */
503  else if ( p_dot > 0.95 )
504  {
505  vector_difference(P2, P1, &P3);
506  normalize(&P3);
507  }
508  /* Just keep the current angle in A1/A3. */
509  else
510  {
511  P3 = *P2;
512  }
513 
514  /* Normals to the A-plane and B-plane */
515  cross_product(P1, &P3, normal);
516  normalize(normal);
517 }
void normalize(POINT3D *p)
Normalize to a unit vector.
Definition: lwgeodetic.c:565
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:396
static void vector_difference(const POINT3D *a, const POINT3D *b, POINT3D *n)
Calculate the difference of two vectors.
Definition: lwgeodetic.c:426
void vector_sum(const POINT3D *a, const POINT3D *b, POINT3D *n)
Calculate the sum of two vectors.
Definition: lwgeodetic.c:415
static void cross_product(const POINT3D *a, const POINT3D *b, POINT3D *n)
Calculate the cross product of two vectors.
Definition: lwgeodetic.c:404
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