ptarray_area_spheroid()

static double ptarray_area_spheroid ( const POINTARRAY *  pa, const SPHEROID *  spheroid  )

static

Definition at line 142 of file lwspheroid.c.

{
        /* Return zero on non-sensical inputs */
        if ( ! pa || pa->npoints < 4 )
                return 0.0;
 
        struct geod_geodesic gd;
        geod_init(&gd, spheroid->a, spheroid->f);
        struct geod_polygon poly;
        geod_polygon_init(&poly, 0);
        uint32_t i;
        double area; /* returned polygon area */
        POINT2D p; /* long/lat units are degrees */
 
        /* Pass points from point array; don't close the linearring */
        for ( i = 0; i < pa->npoints - 1; i++ )
        {
                getPoint2d_p(pa, i, &p);
                geod_polygon_addpoint(&gd, &poly, p.y, p.x);
                LWDEBUGF(4, "geod_polygon_addpoint %d: %.12g %.12g", i, p.y, p.x);
        }
        i = geod_polygon_compute(&gd, &poly, 0, 1, &area, 0);
        if ( i != pa->npoints - 1 )
        {
                lwerror("ptarray_area_spheroid: different number of points %d vs %d",
                                i, pa->npoints - 1);
        }
        LWDEBUGF(4, "geod_polygon_compute area: %.12g", area);
        return fabs(area);
}

References SPHEROID::a, SPHEROID::f, getPoint2d_p(), LWDEBUGF, lwerror(), POINTARRAY::npoints, POINT2D::x, and POINT2D::y.

Referenced by lwgeom_area_spheroid().

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