PostGIS  2.1.10dev-r@@SVN_REVISION@@
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.

Good even for small distances between p and q.

Definition at line 583 of file lwgeodetic.c.

References GEOGRAPHIC_POINT::lat, GEOGRAPHIC_POINT::lon, POINT3D::x, POINT3D::y, and POINT3D::z.

Referenced by clairaut_geographic(), edge_distance_to_point(), edge_intersection(), edge_point_side(), and sphere_angle().

584 {
585  double lon_qpp = (q->lon + p->lon) / -2.0;
586  double lon_qmp = (q->lon - p->lon) / 2.0;
587  double sin_p_lat_minus_q_lat = sin(p->lat-q->lat);
588  double sin_p_lat_plus_q_lat = sin(p->lat+q->lat);
589  double sin_lon_qpp = sin(lon_qpp);
590  double sin_lon_qmp = sin(lon_qmp);
591  double cos_lon_qpp = cos(lon_qpp);
592  double cos_lon_qmp = cos(lon_qmp);
593  a->x = sin_p_lat_minus_q_lat * sin_lon_qpp * cos_lon_qmp -
594  sin_p_lat_plus_q_lat * cos_lon_qpp * sin_lon_qmp;
595  a->y = sin_p_lat_minus_q_lat * cos_lon_qpp * cos_lon_qmp +
596  sin_p_lat_plus_q_lat * sin_lon_qpp * sin_lon_qmp;
597  a->z = cos(p->lat) * cos(q->lat) * sin(q->lon-p->lon);
598 }
double y
Definition: liblwgeom.h:296
double x
Definition: liblwgeom.h:296
double z
Definition: liblwgeom.h:296

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