PostGIS  2.5.0dev-r@@SVN_REVISION@@

◆ clairaut_geographic()

int clairaut_geographic ( const GEOGRAPHIC_POINT start,
const GEOGRAPHIC_POINT end,
GEOGRAPHIC_POINT g_top,
GEOGRAPHIC_POINT g_bottom 
)

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

Definition at line 1070 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().

1071 {
1072  POINT3D t1, t2;
1073  GEOGRAPHIC_POINT vN1, vN2;
1074  LWDEBUG(4,"entering function");
1075  robust_cross_product(start, end, &t1);
1076  normalize(&t1);
1077  robust_cross_product(end, start, &t2);
1078  normalize(&t2);
1079  LWDEBUGF(4, "unit normal t1 == POINT(%.8g %.8g %.8g)", t1.x, t1.y, t1.z);
1080  LWDEBUGF(4, "unit normal t2 == POINT(%.8g %.8g %.8g)", t2.x, t2.y, t2.z);
1081  cart2geog(&t1, &vN1);
1082  cart2geog(&t2, &vN2);
1083  g_top->lat = z_to_latitude(t1.z,LW_TRUE);
1084  g_top->lon = vN2.lon;
1085  g_bottom->lat = z_to_latitude(t2.z,LW_FALSE);
1086  g_bottom->lon = vN1.lon;
1087  LWDEBUGF(4, "clairaut top == GPOINT(%.6g %.6g)", g_top->lat, g_top->lon);
1088  LWDEBUGF(4, "clairaut bottom == GPOINT(%.6g %.6g)", g_bottom->lat, g_bottom->lon);
1089  return LW_SUCCESS;
1090 }
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:603
void normalize(POINT3D *p)
Normalize to a unit vector.
Definition: lwgeodetic.c:584
double y
Definition: liblwgeom.h:342
double z_to_latitude(double z, int top)
Used in great circle to compute the pole of the great circle.
Definition: lwgeodetic.c:1018
#define LW_SUCCESS
Definition: liblwgeom.h:79
void cart2geog(const POINT3D *p, GEOGRAPHIC_POINT *g)
Convert cartesian coordinates on unit sphere to spherical coordinates.
Definition: lwgeodetic.c:383
#define LWDEBUG(level, msg)
Definition: lwgeom_log.h:83
double x
Definition: liblwgeom.h:342
Point in spherical coordinates on the world.
Definition: lwgeodetic.h:47
double z
Definition: liblwgeom.h:342
#define LW_FALSE
Definition: liblwgeom.h:76
#define LW_TRUE
Return types for functions with status returns.
Definition: liblwgeom.h:75
#define LWDEBUGF(level, msg,...)
Definition: lwgeom_log.h:88
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