gbox_get_sortable_hash()

uint64_t gbox_get_sortable_hash	(	const GBOX *	g,
		const int32_t	srid
	)

Return a sortable key based on the center point of the GBOX.

Definition at line 808 of file gbox.c.

{
        union floatuint {
                uint32_t u;
                float f;
        };
 
        union floatuint x, y;
 
        /*
        * Since in theory the bitwise representation of an IEEE
        * float is sortable (exponents come before mantissa, etc)
        * we just copy the bits directly into an int and then
        * interleave those ints.
        */
        if (FLAGS_GET_GEODETIC(g->flags))
        {
                GEOGRAPHIC_POINT gpt;
                POINT3D p;
                p.x = (g->xmax + g->xmin) / 2.0;
                p.y = (g->ymax + g->ymin) / 2.0;
                p.z = (g->zmax + g->zmin) / 2.0;
                normalize(&p);
                cart2geog(&p, &gpt);
                /* We know range for geography, so build the curve taking it into account */
                x.f = 1.5 + gpt.lon / 512.0;
                y.f = 1.5 + gpt.lat / 256.0;
        }
        else
        {
                x.f = (g->xmax + g->xmin) / 2;
                y.f = (g->ymax + g->ymin) / 2;
                /*
                 * Tweak for popular SRID values: push floating point values into 1..2 range,
                 * a region where exponent is constant and thus Hilbert curve
                 * doesn't have compression artifact when X or Y value is close to 0.
                 * If someone has out of bounds value it will still expose the arifact but not crash.
                 * TODO: reconsider when we will have machinery to properly get bounds by SRID.
                 */
                if (srid == 3857 || srid == 3395)
                {
                        x.f = 1.5 + x.f / 67108864.0;
                        y.f = 1.5 + y.f / 67108864.0;
                }
                else if (srid == 4326)
                {
                        x.f = 1.5 + x.f / 512.0;
                        y.f = 1.5 + y.f / 256.0;
                }
        }
 
        return uint32_hilbert(y.u, x.u);
}

References cart2geog(), GBOX::flags, FLAGS_GET_GEODETIC, GEOGRAPHIC_POINT::lat, GEOGRAPHIC_POINT::lon, normalize(), uint32_hilbert(), POINT3D::x, pixval::x, GBOX::xmax, GBOX::xmin, POINT3D::y, pixval::y, GBOX::ymax, GBOX::ymin, POINT3D::z, GBOX::zmax, and GBOX::zmin.

Referenced by gserialized_cmp(), gserialized_get_sortable_hash(), and rect_node_cmp().

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