mvt_geom()

LWGEOM* mvt_geom	(	const LWGEOM *	lwgeom,
		const GBOX *	gbox,
		uint32_t	extent,
		uint32_t	buffer,
		bool	clip_geom
	)

Transform a geometry into vector tile coordinate space.

Makes best effort to keep validity. Might collapse geometry into lower dimension.

Definition at line 710 of file mvt.c.

References AFFINE::afac, buffer(), AFFINE::efac, GBOX::flags, FLAGS_SET_GEODETIC, gbox_contains_2d(), gbox_init(), gbox_overlaps_2d(), AFFINE::ifac, gridspec_t::ipx, gridspec_t::ipy, lwgeom_affine(), lwgeom_calculate_gbox(), lwgeom_clip_by_rect(), lwgeom_clone_deep(), lwgeom_force_clockwise(), lwgeom_free(), lwgeom_get_basic_type(), lwgeom_get_bbox(), lwgeom_grid(), lwgeom_intersection(), lwgeom_is_empty(), lwgeom_make_valid(), lwgeom_reverse(), lwgeom_to_basic_type(), lwpoly_as_lwgeom(), lwpoly_construct_envelope(), lwpoly_free(), POLYGONTYPE, GBOX::xmax, GBOX::xmin, AFFINE::xoff, gridspec_t::xsize, GBOX::ymax, GBOX::ymin, AFFINE::yoff, and gridspec_t::ysize.

Referenced by ST_AsMVTGeom().

{
        AFFINE affine;
        gridspec grid;
        LWGEOM *lwgeom_out = NULL;
        double width = gbox->xmax - gbox->xmin;
        double height = gbox->ymax - gbox->ymin;
        double fx = extent / width;
        double fy = -(extent / height);
        uint8_t basic_type;
        POSTGIS_DEBUG(2, "mvt_geom called");

        /* Short circuit out on EMPTY */
        if (lwgeom_is_empty(lwgeom))
                return NULL;

        if (width == 0 || height == 0)
                elog(ERROR, "mvt_geom: bounds width or height cannot be 0");

        if (extent == 0)
                elog(ERROR, "mvt_geom: extent cannot be 0");

        lwgeom_out = lwgeom_clone_deep(lwgeom);
        basic_type = lwgeom_get_basic_type(lwgeom_out);

        /* transform to tile coordinate space */
        memset(&affine, 0, sizeof(affine));
        affine.afac = fx;
        affine.efac = fy;
        affine.ifac = 1;
        affine.xoff = -gbox->xmin * fx;
        affine.yoff = -gbox->ymax * fy;
        lwgeom_affine(lwgeom_out, &affine);

        /* snap to integer precision, removing duplicate points */
        memset(&grid, 0, sizeof(gridspec));
        grid.ipx = 0;
        grid.ipy = 0;
        grid.xsize = 1;
        grid.ysize = 1;
        lwgeom_out = lwgeom_grid(lwgeom_out, &grid);

        if (lwgeom_out == NULL || lwgeom_is_empty(lwgeom_out))
                return NULL;

        if (clip_geom)
        {
                GBOX bgbox, lwgeom_gbox;
                gbox_init(&bgbox);
                gbox_init(&lwgeom_gbox);
                bgbox.xmax = bgbox.ymax = (double)extent + (double)buffer;
                bgbox.xmin = bgbox.ymin = -(double)buffer;
                FLAGS_SET_GEODETIC(lwgeom_gbox.flags, 0);
                FLAGS_SET_GEODETIC(bgbox.flags, 0);
                lwgeom_calculate_gbox(lwgeom_out, &lwgeom_gbox);

                if (!gbox_overlaps_2d(&lwgeom_gbox, &bgbox))
                {
                        POSTGIS_DEBUG(3, "mvt_geom: geometry outside clip box");
                        return NULL;
                }

                if (!gbox_contains_2d(&bgbox, &lwgeom_gbox))
                {
                        LWGEOM *clipped_geom;
#if POSTGIS_GEOS_VERSION < 35
                        LWPOLY *lwenv = lwpoly_construct_envelope(0, bgbox.xmin, bgbox.ymin, bgbox.xmax, bgbox.ymax);
                        clipped_geom = lwgeom_intersection(lwgeom_out, lwpoly_as_lwgeom(lwenv));
                        lwpoly_free(lwenv);
#else
                        clipped_geom = lwgeom_clip_by_rect(lwgeom_out, bgbox.xmin, bgbox.ymin, bgbox.xmax, bgbox.ymax);
#endif
                        if (clipped_geom == NULL || lwgeom_is_empty(clipped_geom))
                        {
                                POSTGIS_DEBUG(3, "mvt_geom: no geometry after clip");
                                return NULL;
                        }

                        /* For some polygons, the simplify step might have left them
                         * as invalid, which can cause clipping to return the complementary
                         * geometry of what it should */
                        if ((basic_type == POLYGONTYPE) &&
                            !gbox_contains_2d(&lwgeom_gbox, lwgeom_get_bbox(clipped_geom)))
                        {
                                /* TODO: Adapt this when and if Exception Policies are introduced.
                                 * Other options would be to fix the geometry and retry
                                 * or to calculate the difference between the 2 boxes.
                                 */
                                POSTGIS_DEBUG(3, "mvt_geom: Invalid geometry after clipping");
                                lwgeom_free(clipped_geom);
                                return NULL;
                        }

                        lwgeom_out = clipped_geom;
                }
        }

        if (lwgeom_out == NULL || lwgeom_is_empty(lwgeom_out))
                return NULL;

        /* if polygon(s) make valid and force clockwise as per MVT spec */
        if (basic_type == POLYGONTYPE)
        {
                lwgeom_out = lwgeom_make_valid(lwgeom_out);

                /* Because we are in image coordinates, we need to go to CCW in */
                /* order to get a CW output in image space */
                lwgeom_force_clockwise(lwgeom_out);
                lwgeom_reverse(lwgeom_out);
        }

        /* Make sure we return the most basic type after simplification and validation */
        lwgeom_out = lwgeom_to_basic_type(lwgeom_out, basic_type);
        if (basic_type != lwgeom_get_basic_type(lwgeom_out))
        {
                /* Drop type changes to play nice with MVT renderers */
                POSTGIS_DEBUG(3, "mvt_geom: Dropping geometry after type change");
                return NULL;
        }

        if (lwgeom_out == NULL || lwgeom_is_empty(lwgeom_out))
                return NULL;


        /* Clipping and validation might produce float values. Grid again into int
         * and pray that the output is still valid */
        lwgeom_out = lwgeom_grid(lwgeom_out, &grid);

        if (lwgeom_out == NULL || lwgeom_is_empty(lwgeom_out))
                return NULL;

        return lwgeom_out;
}

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