mvt_grid_and_validate_geos()

static LWGEOM * mvt_grid_and_validate_geos ( LWGEOM *  ng, uint8_t  basic_type  )

static

Given a geometry, it uses GEOS operations to make sure that it's valid according to the MVT spec and that all points are snapped into int coordinates It iterates several times if needed, if it fails, returns NULL.

Definition at line 1020 of file mvt.c.

{
        gridspec grid = {0, 0, 0, 0, 1, 1, 0, 0};
        ng = lwgeom_to_basic_type(ng, basic_type);
 
        if (basic_type != POLYGONTYPE)
        {
                /* Make sure there is no pending float values (clipping can do that) */
                lwgeom_grid_in_place(ng, &grid);
        }
        else
        {
                /* For polygons we have to both snap to the integer grid and force validation.
                 * The problem with this procedure is that snapping to the grid can create
                 * an invalid geometry and making it valid can create float values; so
                 * we iterate several times (up to 3) to generate a valid geom with int coordinates
                 */
                GEOSGeometry *geo;
                uint32_t iterations = 0;
                static const uint32_t max_iterations = 3;
                bool valid = false;
 
                /* Grid to int */
                lwgeom_grid_in_place(ng, &grid);
 
                initGEOS(lwgeom_geos_error, lwgeom_geos_error);
                geo = LWGEOM2GEOS(ng, 0);
                if (!geo)
                        return NULL;
                valid = GEOSisValid(geo) == 1;
 
                while (!valid && iterations < max_iterations)
                {
#if POSTGIS_GEOS_VERSION < 38
                        GEOSGeometry *geo_valid = LWGEOM_GEOS_makeValid(geo);
#else
                        GEOSGeometry *geo_valid = GEOSMakeValid(geo);
#endif
 
                        GEOSGeom_destroy(geo);
                        if (!geo_valid)
                                return NULL;
 
                        ng = GEOS2LWGEOM(geo_valid, 0);
                        GEOSGeom_destroy(geo_valid);
                        if (!ng)
                                return NULL;
 
                        lwgeom_grid_in_place(ng, &grid);
                        ng = lwgeom_to_basic_type(ng, basic_type);
                        geo = LWGEOM2GEOS(ng, 0);
                        valid = GEOSisValid(geo) == 1;
                        iterations++;
                }
                GEOSGeom_destroy(geo);
 
                if (!valid)
                {
                        POSTGIS_DEBUG(1, "mvt_geom: Could not transform into a valid MVT geometry");
                        return NULL;
                }
 
                /* In image coordinates CW actually comes out a CCW, so we reverse */
                lwgeom_force_clockwise(ng);
                lwgeom_reverse_in_place(ng);
        }
        return ng;
}

References GEOS2LWGEOM(), LWGEOM2GEOS(), lwgeom_force_clockwise(), lwgeom_geos_error(), lwgeom_grid_in_place(), lwgeom_reverse_in_place(), lwgeom_to_basic_type(), and POLYGONTYPE.

Referenced by mvt_clip_and_validate_geos().

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