/**
* Calculate the area of an LWGEOM. Anything except POLYGON, MULTIPOLYGON
* and GEOMETRYCOLLECTION return zero immediately. Multi's recurse, polygons
* calculate external ring area and subtract internal ring area. A GBOX is
* required to check relationship to equator an outside point.
* WARNING: Does NOT WORK for polygons over equator or pole.
*/
double lwgeom_area_spheroid(const LWGEOM *lwgeom, const GBOX *gbox, const SPHEROID *spheroid)
{
int type;
assert(lwgeom);
/* No area in nothing */
if ( lwgeom_is_empty(lwgeom) )
return 0.0;
/* Read the geometry type number */
type = TYPE_GETTYPE(lwgeom->type);
/* Anything but polygons and collections returns zero */
if ( ! ( type == POLYGONTYPE || type == MULTIPOLYGONTYPE || type == COLLECTIONTYPE ) )
return 0.0;
/* Actually calculate area */
if ( type == POLYGONTYPE )
{
LWPOLY *poly = (LWPOLY*)lwgeom;
int i;
double area = 0.0;
/* Just in case there's no rings */
if ( poly->nrings < 1 )
return 0.0;
/* First, the area of the outer ring */
area += ptarray_area_spheroid(poly->rings[0], spheroid);
/* Subtract areas of inner rings */
for ( i = 1; i < poly->nrings; i++ )
{
area -= ptarray_area_spheroid(poly->rings[i], spheroid);
}
return area;
}
/* Recurse into sub-geometries to get area */
if ( type == MULTIPOLYGONTYPE || type == COLLECTIONTYPE )
{
LWCOLLECTION *col = (LWCOLLECTION*)lwgeom;
int i;
double area = 0.0;
for ( i = 0; i < col->ngeoms; i++ )
{
area += lwgeom_area_spheroid(col->geoms[i], gbox, spheroid);
}
return area;
}
/* Shouldn't get here. */
return 0.0;
}
static VALUE get_area_from_wkt(VALUE self, VALUE geom_wkt)
{
lwg = lwgeom_from_wkt(RSTRING_PTR(geom_wkt), 0);
double area = lwgeom_area_spheroid(lwg, &s);
return rb_float_new(area);
}
double get_area_for_lwg()
{
double area = lwgeom_area_spheroid(lwg, &s);
lwgeom_free(lwg);
return area;
}
