mvt_safe_clip_polygon_by_box()

static LWGEOM* mvt_safe_clip_polygon_by_box ( LWGEOM *  lwg_in, GBOX *  clip_box  )

static

Clips an input geometry using GEOSIntersection It used to try to use GEOSClipByRect (as mvt_unsafe_clip_by_box) but since that produces invalid output when an invalid geometry is given and detecting it resulted to be impossible, we use intersection instead and, upon error, force validation of the input and retry.

Might return NULL

Definition at line 831 of file mvt.c.

{
        LWGEOM *geom_clipped, *envelope;
        GBOX geom_box;
        GEOSGeometry *geos_input, *geos_box, *geos_result;
 
        gbox_init(&geom_box);
        FLAGS_SET_GEODETIC(geom_box.flags, 0);
        lwgeom_calculate_gbox(lwg_in, &geom_box);
 
        if (!gbox_overlaps_2d(&geom_box, clip_box))
        {
                POSTGIS_DEBUG(3, "mvt_geom: geometry outside clip box");
                return NULL;
        }
 
        if (gbox_contains_2d(clip_box, &geom_box))
        {
                POSTGIS_DEBUG(3, "mvt_geom: geometry contained fully inside the box");
                return lwg_in;
        }
 
        initGEOS(lwnotice, lwgeom_geos_error);
        if (!(geos_input = LWGEOM2GEOS(lwg_in, 1)))
                return NULL;
 
        envelope = (LWGEOM *)lwpoly_construct_envelope(
            lwg_in->srid, clip_box->xmin, clip_box->ymin, clip_box->xmax, clip_box->ymax);
        geos_box = LWGEOM2GEOS(envelope, 1);
        lwgeom_free(envelope);
        if (!geos_box)
        {
                GEOSGeom_destroy(geos_input);
                return NULL;
        }
 
        geos_result = GEOSIntersection(geos_input, geos_box);
        if (!geos_result)
        {
                POSTGIS_DEBUG(3, "mvt_geom: no geometry after intersection. Retrying after validation");
                GEOSGeom_destroy(geos_input);
                lwg_in = lwgeom_make_valid(lwg_in);
                if (!(geos_input = LWGEOM2GEOS(lwg_in, 1)))
                {
                        GEOSGeom_destroy(geos_box);
                        return NULL;
                }
                geos_result = GEOSIntersection(geos_input, geos_box);
                if (!geos_result)
                {
                        GEOSGeom_destroy(geos_box);
                        GEOSGeom_destroy(geos_input);
                        return NULL;
                }
        }
 
        GEOSSetSRID(geos_result, lwg_in->srid);
        geom_clipped = GEOS2LWGEOM(geos_result, 0);
 
        GEOSGeom_destroy(geos_box);
        GEOSGeom_destroy(geos_input);
        GEOSGeom_destroy(geos_result);
 
        if (!geom_clipped || lwgeom_is_empty(geom_clipped))
        {
                POSTGIS_DEBUG(3, "mvt_geom: no geometry after clipping");
                return NULL;
        }
 
        return geom_clipped;
}

References GBOX::flags, FLAGS_SET_GEODETIC, gbox_contains_2d(), gbox_init(), gbox_overlaps_2d(), GEOS2LWGEOM(), LWGEOM2GEOS(), lwgeom_calculate_gbox(), lwgeom_free(), lwgeom_geos_error(), lwgeom_is_empty(), lwgeom_make_valid(), lwnotice(), lwpoly_construct_envelope(), LWGEOM::srid, GBOX::xmax, GBOX::xmin, GBOX::ymax, and GBOX::ymin.

Referenced by mvt_iterate_clip_by_box_geos().

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