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 3424 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().

3425 {
3426  POINT3D AN, BN, VN; /* Normals to plane A and plane B */
3427  double ab_dot;
3428  int a1_side, a2_side, b1_side, b2_side;
3429  int rv = PIR_NO_INTERACT;
3430 
3431  /* Normals to the A-plane and B-plane */
3432  unit_normal(A1, A2, &AN);
3433  unit_normal(B1, B2, &BN);
3434 
3435  /* Are A-plane and B-plane basically the same? */
3436  ab_dot = dot_product(&AN, &BN);
3437  if ( FP_EQUALS(fabs(ab_dot), 1.0) )
3438  {
3439  /* Co-linear case */
3440  if ( point_in_cone(A1, A2, B1) || point_in_cone(A1, A2, B2) ||
3441  point_in_cone(B1, B2, A1) || point_in_cone(B1, B2, A2) )
3442  {
3443  rv |= PIR_INTERSECTS;
3444  rv |= PIR_COLINEAR;
3445  }
3446  return rv;
3447  }
3448 
3449  /* What side of plane-A and plane-B do the end points */
3450  /* of A and B fall? */
3451  a1_side = dot_product_side(&BN, A1);
3452  a2_side = dot_product_side(&BN, A2);
3453  b1_side = dot_product_side(&AN, B1);
3454  b2_side = dot_product_side(&AN, B2);
3455 
3456  /* Both ends of A on the same side of plane B. */
3457  if ( a1_side == a2_side && a1_side != 0 )
3458  {
3459  /* No intersection. */
3460  return PIR_NO_INTERACT;
3461  }
3462 
3463  /* Both ends of B on the same side of plane A. */
3464  if ( b1_side == b2_side && b1_side != 0 )
3465  {
3466  /* No intersection. */
3467  return PIR_NO_INTERACT;
3468  }
3469 
3470  /* A straddles B and B straddles A, so... */
3471  if ( a1_side != a2_side && (a1_side + a2_side) == 0 &&
3472  b1_side != b2_side && (b1_side + b2_side) == 0 )
3473  {
3474  /* Have to check if intersection point is inside both arcs */
3475  unit_normal(&AN, &BN, &VN);
3476  if ( point_in_cone(A1, A2, &VN) && point_in_cone(B1, B2, &VN) )
3477  {
3478  return PIR_INTERSECTS;
3479  }
3480 
3481  /* Have to check if intersection point is inside both arcs */
3482  vector_scale(&VN, -1);
3483  if ( point_in_cone(A1, A2, &VN) && point_in_cone(B1, B2, &VN) )
3484  {
3485  return PIR_INTERSECTS;
3486  }
3487 
3488  return PIR_NO_INTERACT;
3489  }
3490 
3491  /* The rest are all intersects variants... */
3492  rv |= PIR_INTERSECTS;
3493 
3494  /* A touches B */
3495  if ( a1_side == 0 )
3496  {
3497  /* Touches at A1, A2 is on what side? */
3498  rv |= (a2_side < 0 ? PIR_A_TOUCH_RIGHT : PIR_A_TOUCH_LEFT);
3499  }
3500  else if ( a2_side == 0 )
3501  {
3502  /* Touches at A2, A1 is on what side? */
3503  rv |= (a1_side < 0 ? PIR_A_TOUCH_RIGHT : PIR_A_TOUCH_LEFT);
3504  }
3505 
3506  /* B touches A */
3507  if ( b1_side == 0 )
3508  {
3509  /* Touches at B1, B2 is on what side? */
3510  rv |= (b2_side < 0 ? PIR_B_TOUCH_RIGHT : PIR_B_TOUCH_LEFT);
3511  }
3512  else if ( b2_side == 0 )
3513  {
3514  /* Touches at B2, B1 is on what side? */
3515  rv |= (b1_side < 0 ? PIR_B_TOUCH_RIGHT : PIR_B_TOUCH_LEFT);
3516  }
3517 
3518  return rv;
3519 }
#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:3409
static void vector_scale(POINT3D *n, double scale)
Scale a vector out by a factor.
Definition: lwgeodetic.c:456
#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:510
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:415
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:3371
#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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