PostGIS  2.1.10dev-r@@SVN_REVISION@@
int edge_intersection ( const GEOGRAPHIC_EDGE e1,
const GEOGRAPHIC_EDGE e2,
GEOGRAPHIC_POINT g 
)

Returns true if an intersection can be calculated, and places it in *g.

Returns false otherwise.

Definition at line 1074 of file lwgeodetic.c.

References dot_product(), edge_contains_point(), GEOGRAPHIC_EDGE::end, FP_EQUALS, geographic_point_equals(), GEOGRAPHIC_POINT::lat, GEOGRAPHIC_POINT::lon, LW_FALSE, LW_TRUE, LWDEBUG, LWDEBUGF, normalize(), rad2deg, robust_cross_product(), GEOGRAPHIC_EDGE::start, unit_normal(), POINT3D::x, POINT3D::y, and POINT3D::z.

Referenced by circ_tree_distance_tree_internal(), and test_edge_intersection().

1075 {
1076  POINT3D ea, eb, v;
1077  LWDEBUGF(4, "e1 start(%.20g %.20g) end(%.20g %.20g)", e1->start.lat, e1->start.lon, e1->end.lat, e1->end.lon);
1078  LWDEBUGF(4, "e2 start(%.20g %.20g) end(%.20g %.20g)", e2->start.lat, e2->start.lon, e2->end.lat, e2->end.lon);
1079 
1080  LWDEBUGF(4, "e1 start(%.20g %.20g) end(%.20g %.20g)", rad2deg(e1->start.lon), rad2deg(e1->start.lat), rad2deg(e1->end.lon), rad2deg(e1->end.lat));
1081  LWDEBUGF(4, "e2 start(%.20g %.20g) end(%.20g %.20g)", rad2deg(e2->start.lon), rad2deg(e2->start.lat), rad2deg(e2->end.lon), rad2deg(e2->end.lat));
1082 
1083  if ( geographic_point_equals(&(e1->start), &(e2->start)) )
1084  {
1085  *g = e1->start;
1086  return LW_TRUE;
1087  }
1088  if ( geographic_point_equals(&(e1->end), &(e2->end)) )
1089  {
1090  *g = e1->end;
1091  return LW_TRUE;
1092  }
1093  if ( geographic_point_equals(&(e1->end), &(e2->start)) )
1094  {
1095  *g = e1->end;
1096  return LW_TRUE;
1097  }
1098  if ( geographic_point_equals(&(e1->start), &(e2->end)) )
1099  {
1100  *g = e1->start;
1101  return LW_TRUE;
1102  }
1103 
1104  robust_cross_product(&(e1->start), &(e1->end), &ea);
1105  normalize(&ea);
1106  robust_cross_product(&(e2->start), &(e2->end), &eb);
1107  normalize(&eb);
1108  LWDEBUGF(4, "e1 cross product == POINT(%.12g %.12g %.12g)", ea.x, ea.y, ea.z);
1109  LWDEBUGF(4, "e2 cross product == POINT(%.12g %.12g %.12g)", eb.x, eb.y, eb.z);
1110  LWDEBUGF(4, "fabs(dot_product(ea, eb)) == %.14g", fabs(dot_product(&ea, &eb)));
1111  if ( FP_EQUALS(fabs(dot_product(&ea, &eb)), 1.0) )
1112  {
1113  LWDEBUGF(4, "parallel edges found! dot_product = %.12g", dot_product(&ea, &eb));
1114  /* Parallel (maybe equal) edges! */
1115  /* Hack alert, only returning ONE end of the edge right now, most do better later. */
1116  /* Hack alart #2, returning a value of 2 to indicate a co-linear crossing event. */
1117  if ( edge_contains_point(e1, &(e2->start)) )
1118  {
1119  *g = e2->start;
1120  return 2;
1121  }
1122  if ( edge_contains_point(e1, &(e2->end)) )
1123  {
1124  *g = e2->end;
1125  return 2;
1126  }
1127  if ( edge_contains_point(e2, &(e1->start)) )
1128  {
1129  *g = e1->start;
1130  return 2;
1131  }
1132  if ( edge_contains_point(e2, &(e1->end)) )
1133  {
1134  *g = e1->end;
1135  return 2;
1136  }
1137  }
1138  unit_normal(&ea, &eb, &v);
1139  LWDEBUGF(4, "v == POINT(%.12g %.12g %.12g)", v.x, v.y, v.z);
1140  g->lat = atan2(v.z, sqrt(v.x * v.x + v.y * v.y));
1141  g->lon = atan2(v.y, v.x);
1142  LWDEBUGF(4, "g == GPOINT(%.12g %.12g)", g->lat, g->lon);
1143  LWDEBUGF(4, "g == POINT(%.12g %.12g)", rad2deg(g->lon), rad2deg(g->lat));
1144  if ( edge_contains_point(e1, g) && edge_contains_point(e2, g) )
1145  {
1146  return LW_TRUE;
1147  }
1148  else
1149  {
1150  LWDEBUG(4, "flipping point to other side of sphere");
1151  g->lat = -1.0 * g->lat;
1152  g->lon = g->lon + M_PI;
1153  if ( g->lon > M_PI )
1154  {
1155  g->lon = -1.0 * (2.0 * M_PI - g->lon);
1156  }
1157  if ( edge_contains_point(e1, g) && edge_contains_point(e2, g) )
1158  {
1159  return LW_TRUE;
1160  }
1161  }
1162  return LW_FALSE;
1163 }
void robust_cross_product(const GEOGRAPHIC_POINT *p, const GEOGRAPHIC_POINT *q, POINT3D *a)
Computes the cross product of two vectors using their lat, lng representations.
Definition: lwgeodetic.c:583
void normalize(POINT3D *p)
Normalize to a unit vector.
Definition: lwgeodetic.c:564
int edge_contains_point(const GEOGRAPHIC_EDGE *e, const GEOGRAPHIC_POINT *p)
Returns true if the point p is on the minor edge defined by the end points of e.
Definition: lwgeodetic.c:981
double y
Definition: liblwgeom.h:296
#define LWDEBUG(level, msg)
Definition: lwgeom_log.h:50
double x
Definition: liblwgeom.h:296
double z
Definition: liblwgeom.h:296
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:490
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:397
#define LW_FALSE
Definition: liblwgeom.h:52
#define rad2deg(r)
Definition: lwgeodetic.h:61
GEOGRAPHIC_POINT start
Definition: lwgeodetic.h:44
#define LW_TRUE
Return types for functions with status returns.
Definition: liblwgeom.h:51
GEOGRAPHIC_POINT end
Definition: lwgeodetic.h:45
int geographic_point_equals(const GEOGRAPHIC_POINT *g1, const GEOGRAPHIC_POINT *g2)
Definition: lwgeodetic.c:147
#define FP_EQUALS(A, B)
#define LWDEBUGF(level, msg,...)
Definition: lwgeom_log.h:55

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