static void test_ptarray_signed_area()
{
LWLINE *line;
double area;
/* parallelogram */
line = lwgeom_as_lwline(lwgeom_from_text("LINESTRING(0 0,1 1, 2 1, 1 0, 0 0)"));
area = ptarray_signed_area(line->points);
CU_ASSERT_DOUBLE_EQUAL(area, 1.0, 0.0000001);
lwline_free(line);
/* square */
line = lwgeom_as_lwline(lwgeom_from_text("LINESTRING(0 0,0 2, 2 2, 2 0, 0 0)"));
area = ptarray_signed_area(line->points);
CU_ASSERT_DOUBLE_EQUAL(area, 4.0, 0.0000001);
lwline_free(line);
/* square backwares*/
line = lwgeom_as_lwline(lwgeom_from_text("LINESTRING(0 0,2 0, 2 2, 0 2, 0 0)"));
area = ptarray_signed_area(line->points);
//printf("%g\n",area);
CU_ASSERT_DOUBLE_EQUAL(area, -4.0, 0.0000001);
lwline_free(line);
}
/**
* Find the area of the outer ring - sum (area of inner rings).
*/
double
lwpoly_area(const LWPOLY *poly)
{
double poly_area = 0.0;
int i;
if ( ! poly )
lwerror("lwpoly_area called with null polygon pointer!");
for ( i=0; i < poly->nrings; i++ )
{
POINTARRAY *ring = poly->rings[i];
double ringarea = 0.0;
/* Empty or messed-up ring. */
if ( ring->npoints < 3 )
continue;
ringarea = fabs(ptarray_signed_area(ring));
if ( i == 0 ) /* Outer ring, positive area! */
poly_area += ringarea;
else /* Inner ring, negative area! */
poly_area -= ringarea;
}
return poly_area;
}
int
ptarray_isccw(const POINTARRAY *pa)
{
double area = 0;
area = ptarray_signed_area(pa);
if ( area > 0 ) return LW_FALSE;
else return LW_TRUE;
}