mvt_geom()

LWGEOM* mvt_geom	(	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.

NOTE: modifies in place if possible (not currently possible for polygons)

Definition at line 1081 of file mvt.c.

{
        AFFINE affine = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
        gridspec grid = {0, 0, 0, 0, 1, 1, 0, 0};
        double width = gbox->xmax - gbox->xmin;
        double height = gbox->ymax - gbox->ymin;
        double resx, resy, res, fx, fy;
        const uint8_t basic_type = lwgeom_get_basic_type(lwgeom);
        int preserve_collapsed = LW_FALSE;
        POSTGIS_DEBUG(2, "mvt_geom called");
 
        /* Simplify it as soon as possible */
        lwgeom = lwgeom_to_basic_type(lwgeom, basic_type);
 
        /* 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");
 
        resx = width / extent;
        resy = height / extent;
        res = (resx < resy ? resx : resy)/2;
        fx = extent / width;
        fy = -(extent / height);
 
        /* Remove all non-essential points (under the output resolution) */
        lwgeom_remove_repeated_points_in_place(lwgeom, res);
        lwgeom_simplify_in_place(lwgeom, res, preserve_collapsed);
 
        /* If geometry has disappeared, you're done */
        if (lwgeom_is_empty(lwgeom))
                return NULL;
 
        /* transform to tile coordinate space */
        affine.afac = fx;
        affine.efac = fy;
        affine.ifac = 1;
        affine.xoff = -gbox->xmin * fx;
        affine.yoff = -gbox->ymax * fy;
        lwgeom_affine(lwgeom, &affine);
 
        /* snap to integer precision, removing duplicate points */
        lwgeom_grid_in_place(lwgeom, &grid);
 
        if (lwgeom == NULL || lwgeom_is_empty(lwgeom))
                return NULL;
 
        lwgeom = mvt_clip_and_validate_geos(lwgeom, basic_type, extent, buffer, clip_geom);
        if (lwgeom == NULL || lwgeom_is_empty(lwgeom))
                return NULL;
 
        return lwgeom;
}

References AFFINE::afac, buffer(), AFFINE::efac, AFFINE::ifac, LW_FALSE, lwgeom_affine(), lwgeom_get_basic_type(), lwgeom_grid_in_place(), lwgeom_is_empty(), lwgeom_remove_repeated_points_in_place(), lwgeom_simplify_in_place(), lwgeom_to_basic_type(), mvt_clip_and_validate_geos(), window::res, GBOX::xmax, GBOX::xmin, AFFINE::xoff, GBOX::ymax, GBOX::ymin, and AFFINE::yoff.

Referenced by ST_AsMVTGeom().

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