PostGIS  2.5.2dev-r@@SVN_REVISION@@

◆ edge_intersects()

uint32_t edge_intersects ( const POINT3D A1,
const POINT3D A2,
const POINT3D B1,
const POINT3D B2 
)

Returns non-zero if edges A and B interact.

The type of interaction is given in the return value with the bitmask elements defined above.

Definition at line 3461 of file lwgeodetic.c.

References dot_product(), dot_product_side(), FP_EQUALS, PIR_A_TOUCH_LEFT, PIR_A_TOUCH_RIGHT, PIR_B_TOUCH_LEFT, PIR_B_TOUCH_RIGHT, PIR_COLINEAR, PIR_INTERSECTS, PIR_NO_INTERACT, point_in_cone(), unit_normal(), and vector_scale().

Referenced by circ_tree_contains_point(), circ_tree_distance_tree_internal(), lwpoly_intersects_line(), ptarray_contains_point_sphere(), ptarray_distance_spheroid(), and test_edge_intersects().

3462 {
3463  POINT3D AN, BN, VN; /* Normals to plane A and plane B */
3464  double ab_dot;
3465  int a1_side, a2_side, b1_side, b2_side;
3466  int rv = PIR_NO_INTERACT;
3467 
3468  /* Normals to the A-plane and B-plane */
3469  unit_normal(A1, A2, &AN);
3470  unit_normal(B1, B2, &BN);
3471 
3472  /* Are A-plane and B-plane basically the same? */
3473  ab_dot = dot_product(&AN, &BN);
3474  if ( FP_EQUALS(fabs(ab_dot), 1.0) )
3475  {
3476  /* Co-linear case */
3477  if ( point_in_cone(A1, A2, B1) || point_in_cone(A1, A2, B2) ||
3478  point_in_cone(B1, B2, A1) || point_in_cone(B1, B2, A2) )
3479  {
3480  rv |= PIR_INTERSECTS;
3481  rv |= PIR_COLINEAR;
3482  }
3483  return rv;
3484  }
3485 
3486  /* What side of plane-A and plane-B do the end points */
3487  /* of A and B fall? */
3488  a1_side = dot_product_side(&BN, A1);
3489  a2_side = dot_product_side(&BN, A2);
3490  b1_side = dot_product_side(&AN, B1);
3491  b2_side = dot_product_side(&AN, B2);
3492 
3493  /* Both ends of A on the same side of plane B. */
3494  if ( a1_side == a2_side && a1_side != 0 )
3495  {
3496  /* No intersection. */
3497  return PIR_NO_INTERACT;
3498  }
3499 
3500  /* Both ends of B on the same side of plane A. */
3501  if ( b1_side == b2_side && b1_side != 0 )
3502  {
3503  /* No intersection. */
3504  return PIR_NO_INTERACT;
3505  }
3506 
3507  /* A straddles B and B straddles A, so... */
3508  if ( a1_side != a2_side && (a1_side + a2_side) == 0 &&
3509  b1_side != b2_side && (b1_side + b2_side) == 0 )
3510  {
3511  /* Have to check if intersection point is inside both arcs */
3512  unit_normal(&AN, &BN, &VN);
3513  if ( point_in_cone(A1, A2, &VN) && point_in_cone(B1, B2, &VN) )
3514  {
3515  return PIR_INTERSECTS;
3516  }
3517 
3518  /* Have to check if intersection point is inside both arcs */
3519  vector_scale(&VN, -1);
3520  if ( point_in_cone(A1, A2, &VN) && point_in_cone(B1, B2, &VN) )
3521  {
3522  return PIR_INTERSECTS;
3523  }
3524 
3525  return PIR_NO_INTERACT;
3526  }
3527 
3528  /* The rest are all intersects variants... */
3529  rv |= PIR_INTERSECTS;
3530 
3531  /* A touches B */
3532  if ( a1_side == 0 )
3533  {
3534  /* Touches at A1, A2 is on what side? */
3535  rv |= (a2_side < 0 ? PIR_A_TOUCH_RIGHT : PIR_A_TOUCH_LEFT);
3536  }
3537  else if ( a2_side == 0 )
3538  {
3539  /* Touches at A2, A1 is on what side? */
3540  rv |= (a1_side < 0 ? PIR_A_TOUCH_RIGHT : PIR_A_TOUCH_LEFT);
3541  }
3542 
3543  /* B touches A */
3544  if ( b1_side == 0 )
3545  {
3546  /* Touches at B1, B2 is on what side? */
3547  rv |= (b2_side < 0 ? PIR_B_TOUCH_RIGHT : PIR_B_TOUCH_LEFT);
3548  }
3549  else if ( b2_side == 0 )
3550  {
3551  /* Touches at B2, B1 is on what side? */
3552  rv |= (b1_side < 0 ? PIR_B_TOUCH_RIGHT : PIR_B_TOUCH_LEFT);
3553  }
3554 
3555  return rv;
3556 }
#define PIR_B_TOUCH_RIGHT
Definition: lwgeodetic.h:91
#define PIR_A_TOUCH_RIGHT
Definition: lwgeodetic.h:89
static int dot_product_side(const POINT3D *p, const POINT3D *q)
Utility function for edge_intersects(), signum with a tolerance in determining if the value is zero...
Definition: lwgeodetic.c:3446
static void vector_scale(POINT3D *n, double scale)
Scale a vector out by a factor.
Definition: lwgeodetic.c:465
#define PIR_A_TOUCH_LEFT
Definition: lwgeodetic.h:90
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 cas...
Definition: lwgeodetic.c:519
static double dot_product(const POINT3D *p1, const POINT3D *p2)
Convert cartesian coordinates on unit sphere to lon/lat coordinates static void cart2ll(const POINT3D...
Definition: lwgeodetic.c:424
static int point_in_cone(const POINT3D *A1, const POINT3D *A2, const POINT3D *P)
Utility function for checking if P is within the cone defined by A1/A2.
Definition: lwgeodetic.c:3380
#define FP_EQUALS(A, B)
#define PIR_NO_INTERACT
Bitmask elements for edge_intersects() return value.
Definition: lwgeodetic.h:86
#define PIR_B_TOUCH_LEFT
Definition: lwgeodetic.h:92
#define PIR_COLINEAR
Definition: lwgeodetic.h:88
#define PIR_INTERSECTS
Definition: lwgeodetic.h:87
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