PostGIS  2.2.7dev-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 1703 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().

1704 {
1705  int i;
1706  const POINT2D *p;
1707  GEOGRAPHIC_POINT a, b, c;
1708  double area = 0.0;
1709 
1710  /* Return zero on nonsensical inputs */
1711  if ( ! pa || pa->npoints < 4 )
1712  return 0.0;
1713 
1714  p = getPoint2d_cp(pa, 0);
1715  geographic_point_init(p->x, p->y, &a);
1716  p = getPoint2d_cp(pa, 1);
1717  geographic_point_init(p->x, p->y, &b);
1718 
1719  for ( i = 2; i < pa->npoints-1; i++ )
1720  {
1721  p = getPoint2d_cp(pa, i);
1722  geographic_point_init(p->x, p->y, &c);
1723  area += sphere_signed_area(&a, &b, &c);
1724  b = c;
1725  }
1726 
1727  return fabs(area);
1728 }
int npoints
Definition: liblwgeom.h:355
Datum area(PG_FUNCTION_ARGS)
Point in spherical coordinates on the world.
Definition: lwgeodetic.h:32
double x
Definition: liblwgeom.h:312
const POINT2D * getPoint2d_cp(const POINTARRAY *pa, int n)
Returns a POINT2D pointer into the POINTARRAY serialized_ptlist, suitable for reading from...
Definition: lwgeom_api.c:472
double y
Definition: liblwgeom.h:312
void geographic_point_init(double lon, double lat, GEOGRAPHIC_POINT *g)
Initialize a geographic point.
Definition: lwgeodetic.c:156
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:691

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