PostGIS  2.2.7dev-r@@SVN_REVISION@@
int 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 3099 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(), ptarray_contains_point_sphere(), ptarray_distance_spheroid(), and test_edge_intersects().

3100 {
3101  POINT3D AN, BN, VN; /* Normals to plane A and plane B */
3102  double ab_dot;
3103  int a1_side, a2_side, b1_side, b2_side;
3104  int rv = PIR_NO_INTERACT;
3105 
3106  /* Normals to the A-plane and B-plane */
3107  unit_normal(A1, A2, &AN);
3108  unit_normal(B1, B2, &BN);
3109 
3110  /* Are A-plane and B-plane basically the same? */
3111  ab_dot = dot_product(&AN, &BN);
3112  if ( FP_EQUALS(fabs(ab_dot), 1.0) )
3113  {
3114  /* Co-linear case */
3115  if ( point_in_cone(A1, A2, B1) || point_in_cone(A1, A2, B2) ||
3116  point_in_cone(B1, B2, A1) || point_in_cone(B1, B2, A2) )
3117  {
3118  rv |= PIR_INTERSECTS;
3119  rv |= PIR_COLINEAR;
3120  }
3121  return rv;
3122  }
3123 
3124  /* What side of plane-A and plane-B do the end points */
3125  /* of A and B fall? */
3126  a1_side = dot_product_side(&BN, A1);
3127  a2_side = dot_product_side(&BN, A2);
3128  b1_side = dot_product_side(&AN, B1);
3129  b2_side = dot_product_side(&AN, B2);
3130 
3131  /* Both ends of A on the same side of plane B. */
3132  if ( a1_side == a2_side && a1_side != 0 )
3133  {
3134  /* No intersection. */
3135  return PIR_NO_INTERACT;
3136  }
3137 
3138  /* Both ends of B on the same side of plane A. */
3139  if ( b1_side == b2_side && b1_side != 0 )
3140  {
3141  /* No intersection. */
3142  return PIR_NO_INTERACT;
3143  }
3144 
3145  /* A straddles B and B straddles A, so... */
3146  if ( a1_side != a2_side && (a1_side + a2_side) == 0 &&
3147  b1_side != b2_side && (b1_side + b2_side) == 0 )
3148  {
3149  /* Have to check if intersection point is inside both arcs */
3150  unit_normal(&AN, &BN, &VN);
3151  if ( point_in_cone(A1, A2, &VN) && point_in_cone(B1, B2, &VN) )
3152  {
3153  return PIR_INTERSECTS;
3154  }
3155 
3156  /* Have to check if intersection point is inside both arcs */
3157  vector_scale(&VN, -1);
3158  if ( point_in_cone(A1, A2, &VN) && point_in_cone(B1, B2, &VN) )
3159  {
3160  return PIR_INTERSECTS;
3161  }
3162 
3163  return PIR_NO_INTERACT;
3164  }
3165 
3166  /* The rest are all intersects variants... */
3167  rv |= PIR_INTERSECTS;
3168 
3169  /* A touches B */
3170  if ( a1_side == 0 )
3171  {
3172  /* Touches at A1, A2 is on what side? */
3173  rv |= (a2_side < 0 ? PIR_A_TOUCH_RIGHT : PIR_A_TOUCH_LEFT);
3174  }
3175  else if ( a2_side == 0 )
3176  {
3177  /* Touches at A2, A1 is on what side? */
3178  rv |= (a1_side < 0 ? PIR_A_TOUCH_RIGHT : PIR_A_TOUCH_LEFT);
3179  }
3180 
3181  /* B touches A */
3182  if ( b1_side == 0 )
3183  {
3184  /* Touches at B1, B2 is on what side? */
3185  rv |= (b2_side < 0 ? PIR_B_TOUCH_RIGHT : PIR_B_TOUCH_LEFT);
3186  }
3187  else if ( b2_side == 0 )
3188  {
3189  /* Touches at B2, B1 is on what side? */
3190  rv |= (b1_side < 0 ? PIR_B_TOUCH_RIGHT : PIR_B_TOUCH_LEFT);
3191  }
3192 
3193  return rv;
3194 }
#define PIR_B_TOUCH_RIGHT
Definition: lwgeodetic.h:71
#define PIR_A_TOUCH_RIGHT
Definition: lwgeodetic.h:69
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:3084
static void vector_scale(POINT3D *n, double scale)
Scale a vector out by a factor.
Definition: lwgeodetic.c:437
#define PIR_A_TOUCH_LEFT
Definition: lwgeodetic.h:70
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:491
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 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:3046
#define FP_EQUALS(A, B)
#define PIR_NO_INTERACT
Bitmask elements for edge_intersects() return value.
Definition: lwgeodetic.h:66
#define PIR_B_TOUCH_LEFT
Definition: lwgeodetic.h:72
#define PIR_COLINEAR
Definition: lwgeodetic.h:68
#define PIR_INTERSECTS
Definition: lwgeodetic.h:67

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