PostGIS  2.5.0dev-r@@SVN_REVISION@@
double lwpoly_area ( const LWPOLY poly)

Find the area of the outer ring - sum (area of inner rings).

Definition at line 439 of file lwpoly.c.

References lwerror(), POINTARRAY::npoints, LWPOLY::nrings, ptarray_signed_area(), and LWPOLY::rings.

Referenced by lwcurvepoly_area(), lwgeom_area(), lwmpoly_to_points(), and lwpoly_to_points().

440 {
441  double poly_area = 0.0;
442  uint32_t i;
443 
444  if ( ! poly )
445  lwerror("lwpoly_area called with null polygon pointer!");
446 
447  for ( i=0; i < poly->nrings; i++ )
448  {
449  POINTARRAY *ring = poly->rings[i];
450  double ringarea = 0.0;
451 
452  /* Empty or messed-up ring. */
453  if ( ring->npoints < 3 )
454  continue;
455 
456  ringarea = fabs(ptarray_signed_area(ring));
457  if ( i == 0 ) /* Outer ring, positive area! */
458  poly_area += ringarea;
459  else /* Inner ring, negative area! */
460  poly_area -= ringarea;
461  }
462 
463  return poly_area;
464 }
double ptarray_signed_area(const POINTARRAY *pa)
Returns the area in cartesian units.
Definition: ptarray.c:990
uint32_t nrings
Definition: liblwgeom.h:454
unsigned int uint32_t
Definition: uthash.h:78
POINTARRAY ** rings
Definition: liblwgeom.h:456
void lwerror(const char *fmt,...)
Write a notice out to the error handler.
Definition: lwutil.c:190
uint32_t npoints
Definition: liblwgeom.h:370

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