lwgeom_geos_node.c

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/**********************************************************************
 *
 * PostGIS - Spatial Types for PostgreSQL
 * http://postgis.net
 *
 * PostGIS is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * PostGIS is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with PostGIS.  If not, see <http://www.gnu.org/licenses/>.
 *
 **********************************************************************
 *
 * Copyright (C) 2011 Sandro Santilli <strk@kbt.io>
 *
 **********************************************************************/


#include "lwgeom_geos.h"
#include "liblwgeom_internal.h"

#include <string.h>
#include <assert.h>

static int
lwgeom_ngeoms(const LWGEOM* n)
{
        const LWCOLLECTION* c = lwgeom_as_lwcollection(n);
        if ( c ) return c->ngeoms;
        else return 1;
}

static const LWGEOM*
lwgeom_subgeom(const LWGEOM* g, int n)
{
        const LWCOLLECTION* c = lwgeom_as_lwcollection(g);
        if ( c ) return lwcollection_getsubgeom((LWCOLLECTION*)c, n);
        else return g;
}


static void
lwgeom_collect_endpoints(const LWGEOM* lwg, LWMPOINT* col)
{
        int i, n;
        LWLINE* l;

        switch (lwg->type)
        {
                case MULTILINETYPE:
                        for ( i = 0,
                                n = lwgeom_ngeoms(lwg);
                              i < n; ++i )
                        {
                                lwgeom_collect_endpoints(
                                        lwgeom_subgeom(lwg, i),
                                        col);
                        }
                        break;
                case LINETYPE:
                        l = (LWLINE*)lwg;
                        col = lwmpoint_add_lwpoint(col,
                                lwline_get_lwpoint(l, 0));
                        col = lwmpoint_add_lwpoint(col,
                                lwline_get_lwpoint(l, l->points->npoints-1));
                        break;
                default:
                        lwerror("lwgeom_collect_endpoints: invalid type %s",
                                lwtype_name(lwg->type));
                        break;
        }
}

static LWMPOINT*
lwgeom_extract_endpoints(const LWGEOM* lwg)
{
        LWMPOINT* col = lwmpoint_construct_empty(SRID_UNKNOWN,
                                      FLAGS_GET_Z(lwg->flags),
                                      FLAGS_GET_M(lwg->flags));
        lwgeom_collect_endpoints(lwg, col);

        return col;
}

/* Assumes initGEOS was called already */
/* May return LWPOINT or LWMPOINT */
static LWGEOM*
lwgeom_extract_unique_endpoints(const LWGEOM* lwg)
{
        LWGEOM* ret;
        GEOSGeometry *gepu;
        LWMPOINT *epall = lwgeom_extract_endpoints(lwg);
        GEOSGeometry *gepall = LWGEOM2GEOS((LWGEOM*)epall, 1);
        lwmpoint_free(epall);
        if ( ! gepall ) {
                lwerror("LWGEOM2GEOS: %s", lwgeom_geos_errmsg);
                return NULL;
        }

        /* UnaryUnion to remove duplicates */
        /* TODO: do it all within pgis using indices */
        gepu = GEOSUnaryUnion(gepall);
        if ( ! gepu ) {
                GEOSGeom_destroy(gepall);
                lwerror("GEOSUnaryUnion: %s", lwgeom_geos_errmsg);
                return NULL;
        }
        GEOSGeom_destroy(gepall);

        ret = GEOS2LWGEOM(gepu, FLAGS_GET_Z(lwg->flags));
        GEOSGeom_destroy(gepu);
        if ( ! ret ) {
                lwerror("Error during GEOS2LWGEOM");
                return NULL;
        }

        return ret;
}

/* exported */
extern LWGEOM* lwgeom_node(const LWGEOM* lwgeom_in);
LWGEOM*
lwgeom_node(const LWGEOM* lwgeom_in)
{
        GEOSGeometry *g1, *gn, *gm;
        LWGEOM *ep, *lines;
        LWCOLLECTION *col, *tc;
        int pn, ln, np, nl;

        if ( lwgeom_dimension(lwgeom_in) != 1 ) {
                lwerror("Noding geometries of dimension != 1 is unsupported");
                return NULL;
        }

        initGEOS(lwgeom_geos_error, lwgeom_geos_error);
        g1 = LWGEOM2GEOS(lwgeom_in, 1);
        if ( ! g1 ) {
                lwerror("LWGEOM2GEOS: %s", lwgeom_geos_errmsg);
                return NULL;
        }

        ep = lwgeom_extract_unique_endpoints(lwgeom_in);
        if ( ! ep ) {
                GEOSGeom_destroy(g1);
                lwerror("Error extracting unique endpoints from input");
                return NULL;
        }

        gn = GEOSNode(g1);
        GEOSGeom_destroy(g1);
        if ( ! gn ) {
                lwgeom_free(ep);
                lwerror("GEOSUnaryUnion: %s", lwgeom_geos_errmsg);
                return NULL;
        }

        gm = GEOSLineMerge(gn);
        GEOSGeom_destroy(gn);
        if ( ! gm ) {
                lwgeom_free(ep);
                lwerror("GEOSLineMerge: %s", lwgeom_geos_errmsg);
                return NULL;
        }

        lines = GEOS2LWGEOM(gm, FLAGS_GET_Z(lwgeom_in->flags));
        GEOSGeom_destroy(gm);
        if ( ! lines ) {
                lwgeom_free(ep);
                lwerror("Error during GEOS2LWGEOM");
                return NULL;
        }

        /*
         * Reintroduce endpoints from input, using split-line-by-point.
         * Note that by now we can be sure that each point splits at
         * most _one_ segment as any point shared by multiple segments
         * would already be a node. Also we can be sure that any of
         * the segments endpoints won't split any other segment.
         * We can use the above 2 assertions to early exit the loop.
         */

        col = lwcollection_construct_empty(MULTILINETYPE, lwgeom_in->srid,
                                      FLAGS_GET_Z(lwgeom_in->flags),
                                      FLAGS_GET_M(lwgeom_in->flags));

        np = lwgeom_ngeoms(ep);
        for (pn=0; pn<np; ++pn) { /* for each point */

                const LWPOINT* p = (LWPOINT*)lwgeom_subgeom(ep, pn);

                nl = lwgeom_ngeoms(lines);
                for (ln=0; ln<nl; ++ln) { /* for each line */

                        const LWLINE* l = (LWLINE*)lwgeom_subgeom(lines, ln);

                        int s = lwline_split_by_point_to(l, p, (LWMLINE*)col);

                        if ( ! s ) continue; /* not on this line */

                        if ( s == 1 ) {
                                /* found on this line, but not splitting it */
                                break;
                        }

                        /* splits this line */

                        /* replace this line with the two splits */
                        if ( lwgeom_is_collection(lines) ) {
                                tc = (LWCOLLECTION*)lines;
                                lwcollection_reserve(tc, nl + 1);
                                while (nl > ln+1) {
                                        tc->geoms[nl] = tc->geoms[nl-1];
                                        --nl;
                                }
                                lwgeom_free(tc->geoms[ln]);
                                tc->geoms[ln]   = col->geoms[0];
                                tc->geoms[ln+1] = col->geoms[1];
                                tc->ngeoms++;
                        } else {
                                lwgeom_free(lines);
                                /* transfer ownership rather than cloning */
                                lines = (LWGEOM*)lwcollection_clone_deep(col);
                                assert(col->ngeoms == 2);
                                lwgeom_free(col->geoms[0]);
                                lwgeom_free(col->geoms[1]);
                        }

                        /* reset the vector */
                        assert(col->ngeoms == 2);
                        col->ngeoms = 0;

                        break;
                }

        }

        lwgeom_free(ep);
        lwcollection_free(col);

        lines->srid = lwgeom_in->srid;
        return (LWGEOM*)lines;
}