ST_GeometricMedian()

Datum ST_GeometricMedian

(

PG_FUNCTION_ARGS

)

Definition at line 1241 of file lwgeom_functions_analytic.c.

{
        GSERIALIZED* geom;
        GSERIALIZED* result;
        LWGEOM* input;
        LWPOINT* lwresult;
        static const double min_default_tolerance = 1e-8;
        double tolerance = min_default_tolerance;
        bool compute_tolerance_from_box;
        bool fail_if_not_converged;
        int max_iter;
 
        /* Read and validate our input arguments */
        if (PG_ARGISNULL(0))
                PG_RETURN_NULL();
 
        compute_tolerance_from_box = PG_ARGISNULL(1);
 
        if (!compute_tolerance_from_box)
        {
                tolerance = PG_GETARG_FLOAT8(1);
                if (tolerance < 0)
                {
                        lwpgerror("Tolerance must be positive.");
                        PG_RETURN_NULL();
                }
        }
 
        max_iter = PG_ARGISNULL(2) ? -1 : PG_GETARG_INT32(2);
        fail_if_not_converged = PG_ARGISNULL(3) ? LW_FALSE : PG_GETARG_BOOL(3);
 
        if (max_iter < 0)
        {
                lwpgerror("Maximum iterations must be positive.");
                PG_RETURN_NULL();
        }
 
        /* OK, inputs are valid. */
        geom = PG_GETARG_GSERIALIZED_P(0);
        input = lwgeom_from_gserialized(geom);
 
        if (compute_tolerance_from_box)
        {
                /* Compute a default tolerance based on the smallest dimension
                 * of the geometry's bounding box.
                 */
                static const double tolerance_coefficient = 1e-6;
                const GBOX* box = lwgeom_get_bbox(input);
 
                if (box)
                {
                        double min_dim = FP_MIN(box->xmax - box->xmin, box->ymax - box->ymin);
                        if (lwgeom_has_z(input))
                                min_dim = FP_MIN(min_dim, box->zmax - box->zmin);
 
                        /* Apply a lower bound to the computed default tolerance to
                         * avoid a tolerance of zero in the case of collinear
                         * points.
                         */
                        tolerance = FP_MAX(min_default_tolerance, tolerance_coefficient * min_dim);
                }
        }
 
        lwresult = lwgeom_median(input, tolerance, max_iter, fail_if_not_converged);
        lwgeom_free(input);
 
        if(!lwresult)
        {
                lwpgerror("Error computing geometric median.");
                PG_RETURN_NULL();
        }
 
        result = geometry_serialize(lwpoint_as_lwgeom(lwresult));
 
        PG_RETURN_POINTER(result);
}

References FP_MAX, FP_MIN, geometry_serialize(), LW_FALSE, lwgeom_free(), lwgeom_from_gserialized(), lwgeom_get_bbox(), lwgeom_has_z(), lwgeom_median(), lwpoint_as_lwgeom(), GBOX::xmax, GBOX::xmin, GBOX::ymax, GBOX::ymin, GBOX::zmax, and GBOX::zmin.

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