PostGIS  2.1.10dev-r@@SVN_REVISION@@
int clairaut_geographic ( const GEOGRAPHIC_POINT start,

Computes the pole of the great circle disk which is the intersection of the great circle with the line of maximum/minimum gradiant that lies on the great circle plane.

Definition at line 1048 of file lwgeodetic.c.

References cart2geog(), GEOGRAPHIC_POINT::lat, GEOGRAPHIC_POINT::lon, LW_FALSE, LW_SUCCESS, LW_TRUE, LWDEBUG, LWDEBUGF, normalize(), robust_cross_product(), POINT3D::x, POINT3D::y, POINT3D::z, and z_to_latitude().

Referenced by test_clairaut().

1049 {
1050  POINT3D t1, t2;
1052  LWDEBUG(4,"entering function");
1053  robust_cross_product(start, end, &t1);
1054  normalize(&t1);
1055  robust_cross_product(end, start, &t2);
1056  normalize(&t2);
1057  LWDEBUGF(4, "unit normal t1 == POINT(%.8g %.8g %.8g)", t1.x, t1.y, t1.z);
1058  LWDEBUGF(4, "unit normal t2 == POINT(%.8g %.8g %.8g)", t2.x, t2.y, t2.z);
1059  cart2geog(&t1, &vN1);
1060  cart2geog(&t2, &vN2);
1061  g_top->lat = z_to_latitude(t1.z,LW_TRUE);
1062  g_top->lon = vN2.lon;
1063  g_bottom->lat = z_to_latitude(t2.z,LW_FALSE);
1064  g_bottom->lon = vN1.lon;
1065  LWDEBUGF(4, "clairaut top == GPOINT(%.6g %.6g)", g_top->lat, g_top->lon);
1066  LWDEBUGF(4, "clairaut bottom == GPOINT(%.6g %.6g)", g_bottom->lat, g_bottom->lon);
1067  return LW_SUCCESS;
1068 }
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
double y
Definition: liblwgeom.h:296
double z_to_latitude(double z, int top)
Used in great circle to compute the pole of the great circle.
Definition: lwgeodetic.c:996
#define LW_SUCCESS
Definition: liblwgeom.h:55
void cart2geog(const POINT3D *p, GEOGRAPHIC_POINT *g)
Convert cartesion coordinates on unit sphere to spherical coordinates.
Definition: lwgeodetic.c:365
#define LWDEBUG(level, msg)
Definition: lwgeom_log.h:50
double x
Definition: liblwgeom.h:296
Point in spherical coordinates on the world.
Definition: lwgeodetic.h:33
double z
Definition: liblwgeom.h:296
#define LW_FALSE
Definition: liblwgeom.h:52
#define LW_TRUE
Return types for functions with status returns.
Definition: liblwgeom.h:51
#define LWDEBUGF(level, msg,...)
Definition: lwgeom_log.h:55

Here is the call graph for this function:

Here is the caller graph for this function: