ptarray_area_sphere()

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 1809 of file lwgeodetic.c.

{
        uint32_t i;
        const POINT2D *p;
        GEOGRAPHIC_POINT a, b, c;
        double area = 0.0;
 
        /* Return zero on nonsensical inputs */
        if ( ! pa || pa->npoints < 4 )
                return 0.0;
 
        p = getPoint2d_cp(pa, 0);
        geographic_point_init(p->x, p->y, &a);
        p = getPoint2d_cp(pa, 1);
        geographic_point_init(p->x, p->y, &b);
 
        for ( i = 2; i < pa->npoints-1; i++ )
        {
                p = getPoint2d_cp(pa, i);
                geographic_point_init(p->x, p->y, &c);
                area += sphere_signed_area(&a, &b, &c);
                b = c;
        }
 
        return fabs(area);
}

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

Referenced by lwgeom_area_sphere().

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