PostGIS  2.5.0dev-r@@SVN_REVISION@@
double ptarray_area_sphere ( const POINTARRAY pa)

Returns the area of the ring (ring must be closed) in square radians (surface of the sphere is 4*PI).

Definition at line 1716 of file lwgeodetic.c.

References area(), geographic_point_init(), getPoint2d_cp(), POINTARRAY::npoints, sphere_signed_area(), POINT2D::x, and POINT2D::y.

Referenced by lwgeom_area_sphere().

1717 {
1718  uint32_t i;
1719  const POINT2D *p;
1720  GEOGRAPHIC_POINT a, b, c;
1721  double area = 0.0;
1722 
1723  /* Return zero on nonsensical inputs */
1724  if ( ! pa || pa->npoints < 4 )
1725  return 0.0;
1726 
1727  p = getPoint2d_cp(pa, 0);
1728  geographic_point_init(p->x, p->y, &a);
1729  p = getPoint2d_cp(pa, 1);
1730  geographic_point_init(p->x, p->y, &b);
1731 
1732  for ( i = 2; i < pa->npoints-1; i++ )
1733  {
1734  p = getPoint2d_cp(pa, i);
1735  geographic_point_init(p->x, p->y, &c);
1736  area += sphere_signed_area(&a, &b, &c);
1737  b = c;
1738  }
1739 
1740  return fabs(area);
1741 }
Datum area(PG_FUNCTION_ARGS)
Point in spherical coordinates on the world.
Definition: lwgeodetic.h:47
unsigned int uint32_t
Definition: uthash.h:78
double x
Definition: liblwgeom.h:327
double y
Definition: liblwgeom.h:327
void geographic_point_init(double lon, double lat, GEOGRAPHIC_POINT *g)
Initialize a geographic point.
Definition: lwgeodetic.c:171
static double sphere_signed_area(const GEOGRAPHIC_POINT *a, const GEOGRAPHIC_POINT *b, const GEOGRAPHIC_POINT *c)
Computes the spherical area of a triangle.
Definition: lwgeodetic.c:706
const POINT2D * getPoint2d_cp(const POINTARRAY *pa, uint32_t n)
Returns a POINT2D pointer into the POINTARRAY serialized_ptlist, suitable for reading from...
Definition: lwgeom_api.c:364
uint32_t npoints
Definition: liblwgeom.h:370

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