liblwgeom/lwgeom_geos_clean.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 2009-2010 Sandro Santilli <strk@kbt.io>
 *
 **********************************************************************/


#include "liblwgeom.h"
#include "lwgeom_geos.h"
#include "liblwgeom_internal.h"
#include "lwgeom_log.h"

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

/* #define POSTGIS_DEBUG_LEVEL 4 */
/* #define PARANOIA_LEVEL 2 */
#undef LWGEOM_PROFILE_MAKEVALID


/*
 * Return Nth vertex in GEOSGeometry as a POINT.
 * May return NULL if the geometry has NO vertexex.
 */
GEOSGeometry* LWGEOM_GEOS_getPointN(const GEOSGeometry*, uint32_t);
GEOSGeometry*
LWGEOM_GEOS_getPointN(const GEOSGeometry* g_in, uint32_t n)
{
        uint32_t dims;
        const GEOSCoordSequence* seq_in;
        GEOSCoordSeq seq_out;
        double val;
        uint32_t sz;
        int gn;
        GEOSGeometry* ret;

        switch ( GEOSGeomTypeId(g_in) )
        {
        case GEOS_MULTIPOINT:
        case GEOS_MULTILINESTRING:
        case GEOS_MULTIPOLYGON:
        case GEOS_GEOMETRYCOLLECTION:
        {
                for (gn=0; gn<GEOSGetNumGeometries(g_in); ++gn)
                {
                        const GEOSGeometry* g = GEOSGetGeometryN(g_in, gn);
                        ret = LWGEOM_GEOS_getPointN(g,n);
                        if ( ret ) return ret;
                }
                break;
        }

        case GEOS_POLYGON:
        {
                ret = LWGEOM_GEOS_getPointN(GEOSGetExteriorRing(g_in), n);
                if ( ret ) return ret;
                for (gn=0; gn<GEOSGetNumInteriorRings(g_in); ++gn)
                {
                        const GEOSGeometry* g = GEOSGetInteriorRingN(g_in, gn);
                        ret = LWGEOM_GEOS_getPointN(g, n);
                        if ( ret ) return ret;
                }
                break;
        }

        case GEOS_POINT:
        case GEOS_LINESTRING:
        case GEOS_LINEARRING:
                break;

        }

        seq_in = GEOSGeom_getCoordSeq(g_in);
        if ( ! seq_in ) return NULL;
        if ( ! GEOSCoordSeq_getSize(seq_in, &sz) ) return NULL;
        if ( ! sz ) return NULL;

        if ( ! GEOSCoordSeq_getDimensions(seq_in, &dims) ) return NULL;

        seq_out = GEOSCoordSeq_create(1, dims);
        if ( ! seq_out ) return NULL;

        if ( ! GEOSCoordSeq_getX(seq_in, n, &val) ) return NULL;
        if ( ! GEOSCoordSeq_setX(seq_out, n, val) ) return NULL;
        if ( ! GEOSCoordSeq_getY(seq_in, n, &val) ) return NULL;
        if ( ! GEOSCoordSeq_setY(seq_out, n, val) ) return NULL;
        if ( dims > 2 )
        {
                if ( ! GEOSCoordSeq_getZ(seq_in, n, &val) ) return NULL;
                if ( ! GEOSCoordSeq_setZ(seq_out, n, val) ) return NULL;
        }

        return GEOSGeom_createPoint(seq_out);
}



LWGEOM * lwcollection_make_geos_friendly(LWCOLLECTION *g);
LWGEOM * lwline_make_geos_friendly(LWLINE *line);
LWGEOM * lwpoly_make_geos_friendly(LWPOLY *poly);
POINTARRAY* ring_make_geos_friendly(POINTARRAY* ring);

/*
 * Ensure the geometry is "structurally" valid
 * (enough for GEOS to accept it)
 * May return the input untouched (if already valid).
 * May return geometries of lower dimension (on collapses)
 */
static LWGEOM *
lwgeom_make_geos_friendly(LWGEOM *geom)
{
        LWDEBUGF(2, "lwgeom_make_geos_friendly enter (type %d)", geom->type);
        switch (geom->type)
        {
        case POINTTYPE:
        case MULTIPOINTTYPE:
                /* a point is always valid */
                return geom;
                break;

        case LINETYPE:
                /* lines need at least 2 points */
                return lwline_make_geos_friendly((LWLINE *)geom);
                break;

        case POLYGONTYPE:
                /* polygons need all rings closed and with npoints > 3 */
                return lwpoly_make_geos_friendly((LWPOLY *)geom);
                break;

        case MULTILINETYPE:
        case MULTIPOLYGONTYPE:
        case COLLECTIONTYPE:
                return lwcollection_make_geos_friendly((LWCOLLECTION *)geom);
                break;

        case CIRCSTRINGTYPE:
        case COMPOUNDTYPE:
        case CURVEPOLYTYPE:
        case MULTISURFACETYPE:
        case MULTICURVETYPE:
        default:
                lwerror("lwgeom_make_geos_friendly: unsupported input geometry type: %s (%d)", lwtype_name(geom->type), geom->type);
                break;
        }
        return 0;
}

/*
 * Close the point array, if not already closed in 2d.
 * Returns the input if already closed in 2d, or a newly
 * constructed POINTARRAY.
 * TODO: move in ptarray.c
 */
POINTARRAY* ptarray_close2d(POINTARRAY* ring);
POINTARRAY*
ptarray_close2d(POINTARRAY* ring)
{
        POINTARRAY* newring;

        /* close the ring if not already closed (2d only) */
        if ( ! ptarray_is_closed_2d(ring) )
        {
                /* close it up */
                newring = ptarray_addPoint(ring,
                                           getPoint_internal(ring, 0),
                                           FLAGS_NDIMS(ring->flags),
                                           ring->npoints);
                ring = newring;
        }
        return ring;
}

/* May return the same input or a new one (never zero) */
POINTARRAY*
ring_make_geos_friendly(POINTARRAY* ring)
{
        POINTARRAY* closedring;
        POINTARRAY* ring_in = ring;

        /* close the ring if not already closed (2d only) */
        closedring = ptarray_close2d(ring);
        if (closedring != ring )
        {
                ring = closedring;
        }

        /* return 0 for collapsed ring (after closeup) */

        while ( ring->npoints < 4 )
        {
                POINTARRAY *oring = ring;
                LWDEBUGF(4, "ring has %d points, adding another", ring->npoints);
                /* let's add another... */
                ring = ptarray_addPoint(ring,
                                        getPoint_internal(ring, 0),
                                        FLAGS_NDIMS(ring->flags),
                                        ring->npoints);
                if ( oring != ring_in ) ptarray_free(oring);
        }


        return ring;
}

/* Make sure all rings are closed and have > 3 points.
 * May return the input untouched.
 */
LWGEOM *
lwpoly_make_geos_friendly(LWPOLY *poly)
{
        LWGEOM* ret;
        POINTARRAY **new_rings;
        int i;

        /* If the polygon has no rings there's nothing to do */
        if ( ! poly->nrings ) return (LWGEOM*)poly;

        /* Allocate enough pointers for all rings */
        new_rings = lwalloc(sizeof(POINTARRAY*)*poly->nrings);

        /* All rings must be closed and have > 3 points */
        for (i=0; i<poly->nrings; i++)
        {
                POINTARRAY* ring_in = poly->rings[i];
                POINTARRAY* ring_out = ring_make_geos_friendly(ring_in);

                if ( ring_in != ring_out )
                {
                        LWDEBUGF(3, "lwpoly_make_geos_friendly: ring %d cleaned, now has %d points", i, ring_out->npoints);
                        ptarray_free(ring_in);
                }
                else
                {
                        LWDEBUGF(3, "lwpoly_make_geos_friendly: ring %d untouched", i);
                }

                assert ( ring_out );
                new_rings[i] = ring_out;
        }

        lwfree(poly->rings);
        poly->rings = new_rings;
        ret = (LWGEOM*)poly;

        return ret;
}

/* Need NO or >1 points. Duplicate first if only one. */
LWGEOM *
lwline_make_geos_friendly(LWLINE *line)
{
        LWGEOM *ret;

        if (line->points->npoints == 1) /* 0 is fine, 2 is fine */
        {
#if 1
                /* Duplicate point */
                line->points = ptarray_addPoint(line->points,
                                                getPoint_internal(line->points, 0),
                                                FLAGS_NDIMS(line->points->flags),
                                                line->points->npoints);
                ret = (LWGEOM*)line;
#else
                /* Turn into a point */
                ret = (LWGEOM*)lwpoint_construct(line->srid, 0, line->points);
#endif
                return ret;
        }
        else
        {
                return (LWGEOM*)line;
                /* return lwline_clone(line); */
        }
}

LWGEOM *
lwcollection_make_geos_friendly(LWCOLLECTION *g)
{
        LWGEOM **new_geoms;
        uint32_t i, new_ngeoms=0;
        LWCOLLECTION *ret;

        /* enough space for all components */
        new_geoms = lwalloc(sizeof(LWGEOM *)*g->ngeoms);

        ret = lwalloc(sizeof(LWCOLLECTION));
        memcpy(ret, g, sizeof(LWCOLLECTION));
    ret->maxgeoms = g->ngeoms;

        for (i=0; i<g->ngeoms; i++)
        {
                LWGEOM* newg = lwgeom_make_geos_friendly(g->geoms[i]);
                if ( newg ) new_geoms[new_ngeoms++] = newg;
        }

        ret->bbox = NULL; /* recompute later... */

        ret->ngeoms = new_ngeoms;
        if ( new_ngeoms )
        {
                ret->geoms = new_geoms;
        }
        else
        {
                free(new_geoms);
                ret->geoms = NULL;
        ret->maxgeoms = 0;
        }

        return (LWGEOM*)ret;
}

/*
 * Fully node given linework
 */
static GEOSGeometry*
LWGEOM_GEOS_nodeLines(const GEOSGeometry* lines)
{
        GEOSGeometry* noded;
        GEOSGeometry* point;

        /*
         * Union with first geometry point, obtaining full noding
         * and dissolving of duplicated repeated points
         *
         * TODO: substitute this with UnaryUnion?
         */

        point = LWGEOM_GEOS_getPointN(lines, 0);
        if ( ! point ) return NULL;

        LWDEBUGF(3,
                       "Boundary point: %s",
                       lwgeom_to_ewkt(GEOS2LWGEOM(point, 0)));

        noded = GEOSUnion(lines, point);
        if ( NULL == noded )
        {
                GEOSGeom_destroy(point);
                return NULL;
        }

        GEOSGeom_destroy(point);

        LWDEBUGF(3,
                       "LWGEOM_GEOS_nodeLines: in[%s] out[%s]",
                       lwgeom_to_ewkt(GEOS2LWGEOM(lines, 0)),
                       lwgeom_to_ewkt(GEOS2LWGEOM(noded, 0)));

        return noded;
}

/*
 * We expect initGEOS being called already.
 * Will return NULL on error (expect error handler being called by then)
 *
 */
static GEOSGeometry*
LWGEOM_GEOS_makeValidPolygon(const GEOSGeometry* gin)
{
        GEOSGeom gout;
        GEOSGeom geos_bound;
        GEOSGeom geos_cut_edges, geos_area, collapse_points;
        GEOSGeometry *vgeoms[3]; /* One for area, one for cut-edges */
        unsigned int nvgeoms=0;

        assert (GEOSGeomTypeId(gin) == GEOS_POLYGON ||
                GEOSGeomTypeId(gin) == GEOS_MULTIPOLYGON);

        geos_bound = GEOSBoundary(gin);
        if ( NULL == geos_bound )
        {
                return NULL;
        }

        LWDEBUGF(3,
                       "Boundaries: %s",
                       lwgeom_to_ewkt(GEOS2LWGEOM(geos_bound, 0)));

        /* Use noded boundaries as initial "cut" edges */

#ifdef LWGEOM_PROFILE_MAKEVALID
  lwnotice("ST_MakeValid: noding lines");
#endif


        geos_cut_edges = LWGEOM_GEOS_nodeLines(geos_bound);
        if ( NULL == geos_cut_edges )
        {
                GEOSGeom_destroy(geos_bound);
                lwnotice("LWGEOM_GEOS_nodeLines(): %s", lwgeom_geos_errmsg);
                return NULL;
        }

        /* NOTE: the noding process may drop lines collapsing to points.
         *       We want to retrive any of those */
        {
                GEOSGeometry* pi;
                GEOSGeometry* po;

#ifdef LWGEOM_PROFILE_MAKEVALID
    lwnotice("ST_MakeValid: extracting unique points from bounds");
#endif

                pi = GEOSGeom_extractUniquePoints(geos_bound);
                if ( NULL == pi )
                {
                        GEOSGeom_destroy(geos_bound);
                        lwnotice("GEOSGeom_extractUniquePoints(): %s",
                                 lwgeom_geos_errmsg);
                        return NULL;
                }

                LWDEBUGF(3,
                               "Boundaries input points %s",
                               lwgeom_to_ewkt(GEOS2LWGEOM(pi, 0)));

#ifdef LWGEOM_PROFILE_MAKEVALID
    lwnotice("ST_MakeValid: extracting unique points from cut_edges");
#endif

                po = GEOSGeom_extractUniquePoints(geos_cut_edges);
                if ( NULL == po )
                {
                        GEOSGeom_destroy(geos_bound);
                        GEOSGeom_destroy(pi);
                        lwnotice("GEOSGeom_extractUniquePoints(): %s",
                                 lwgeom_geos_errmsg);
                        return NULL;
                }

                LWDEBUGF(3,
                               "Boundaries output points %s",
                               lwgeom_to_ewkt(GEOS2LWGEOM(po, 0)));

#ifdef LWGEOM_PROFILE_MAKEVALID
    lwnotice("ST_MakeValid: find collapse points");
#endif

                collapse_points = GEOSDifference(pi, po);
                if ( NULL == collapse_points )
                {
                        GEOSGeom_destroy(geos_bound);
                        GEOSGeom_destroy(pi);
                        GEOSGeom_destroy(po);
                        lwnotice("GEOSDifference(): %s", lwgeom_geos_errmsg);
                        return NULL;
                }

                LWDEBUGF(3,
                               "Collapse points: %s",
                               lwgeom_to_ewkt(GEOS2LWGEOM(collapse_points, 0)));

#ifdef LWGEOM_PROFILE_MAKEVALID
    lwnotice("ST_MakeValid: cleanup(1)");
#endif

                GEOSGeom_destroy(pi);
                GEOSGeom_destroy(po);
        }
        GEOSGeom_destroy(geos_bound);

        LWDEBUGF(3,
                       "Noded Boundaries: %s",
                       lwgeom_to_ewkt(GEOS2LWGEOM(geos_cut_edges, 0)));

        /* And use an empty geometry as initial "area" */
        geos_area = GEOSGeom_createEmptyPolygon();
        if ( ! geos_area )
        {
                lwnotice("GEOSGeom_createEmptyPolygon(): %s", lwgeom_geos_errmsg);
                GEOSGeom_destroy(geos_cut_edges);
                return NULL;
        }

        /*
         * See if an area can be build with the remaining edges
         * and if it can, symdifference with the original area.
         * Iterate this until no more polygons can be created
         * with left-over edges.
         */
        while (GEOSGetNumGeometries(geos_cut_edges))
        {
                GEOSGeometry* new_area=0;
                GEOSGeometry* new_area_bound=0;
                GEOSGeometry* symdif=0;
                GEOSGeometry* new_cut_edges=0;

#ifdef LWGEOM_PROFILE_MAKEVALID
    lwnotice("ST_MakeValid: building area from %d edges", GEOSGetNumGeometries(geos_cut_edges));
#endif

                /*
                 * ASSUMPTION: cut_edges should already be fully noded
                 */

                new_area = LWGEOM_GEOS_buildArea(geos_cut_edges);
                if ( ! new_area )   /* must be an exception */
                {
                        GEOSGeom_destroy(geos_cut_edges);
                        GEOSGeom_destroy(geos_area);
                        lwnotice("LWGEOM_GEOS_buildArea() threw an error: %s",
                                 lwgeom_geos_errmsg);
                        return NULL;
                }

                if ( GEOSisEmpty(new_area) )
                {
                        /* no more rings can be build with thes edges */
                        GEOSGeom_destroy(new_area);
                        break;
                }

                /*
                 * We succeeded in building a ring !
                 */

#ifdef LWGEOM_PROFILE_MAKEVALID
    lwnotice("ST_MakeValid: ring built with %d cut edges, saving boundaries", GEOSGetNumGeometries(geos_cut_edges));
#endif

                /*
                 * Save the new ring boundaries first (to compute
                 * further cut edges later)
                 */
                new_area_bound = GEOSBoundary(new_area);
                if ( ! new_area_bound )
                {
                        /* We did check for empty area already so
                         * this must be some other error */
                        lwnotice("GEOSBoundary('%s') threw an error: %s",
                                 lwgeom_to_ewkt(GEOS2LWGEOM(new_area, 0)),
                                 lwgeom_geos_errmsg);
                        GEOSGeom_destroy(new_area);
                        GEOSGeom_destroy(geos_area);
                        return NULL;
                }

#ifdef LWGEOM_PROFILE_MAKEVALID
    lwnotice("ST_MakeValid: running SymDifference with new area");
#endif

                /*
                 * Now symdif new and old area
                 */
                symdif = GEOSSymDifference(geos_area, new_area);
                if ( ! symdif )   /* must be an exception */
                {
                        GEOSGeom_destroy(geos_cut_edges);
                        GEOSGeom_destroy(new_area);
                        GEOSGeom_destroy(new_area_bound);
                        GEOSGeom_destroy(geos_area);
                        lwnotice("GEOSSymDifference() threw an error: %s",
                                 lwgeom_geos_errmsg);
                        return NULL;
                }

                GEOSGeom_destroy(geos_area);
                GEOSGeom_destroy(new_area);
                geos_area = symdif;
                symdif = 0;

                /*
                 * Now let's re-set geos_cut_edges with what's left
                 * from the original boundary.
                 * ASSUMPTION: only the previous cut-edges can be
                 *             left, so we don't need to reconsider
                 *             the whole original boundaries
                 *
                 * NOTE: this is an expensive operation.
                 *
                 */

#ifdef LWGEOM_PROFILE_MAKEVALID
    lwnotice("ST_MakeValid: computing new cut_edges (GEOSDifference)");
#endif

                new_cut_edges = GEOSDifference(geos_cut_edges, new_area_bound);
                GEOSGeom_destroy(new_area_bound);
                if ( ! new_cut_edges )   /* an exception ? */
                {
                        /* cleanup and throw */
                        GEOSGeom_destroy(geos_cut_edges);
                        GEOSGeom_destroy(geos_area);
                        /* TODO: Shouldn't this be an lwerror ? */
                        lwnotice("GEOSDifference() threw an error: %s",
                                 lwgeom_geos_errmsg);
                        return NULL;
                }
                GEOSGeom_destroy(geos_cut_edges);
                geos_cut_edges = new_cut_edges;
        }

#ifdef LWGEOM_PROFILE_MAKEVALID
  lwnotice("ST_MakeValid: final checks");
#endif

        if ( ! GEOSisEmpty(geos_area) )
        {
                vgeoms[nvgeoms++] = geos_area;
        }
        else
        {
                GEOSGeom_destroy(geos_area);
        }

        if ( ! GEOSisEmpty(geos_cut_edges) )
        {
                vgeoms[nvgeoms++] = geos_cut_edges;
        }
        else
        {
                GEOSGeom_destroy(geos_cut_edges);
        }

        if ( ! GEOSisEmpty(collapse_points) )
        {
                vgeoms[nvgeoms++] = collapse_points;
        }
        else
        {
                GEOSGeom_destroy(collapse_points);
        }

        if ( 1 == nvgeoms )
        {
                /* Return cut edges */
                gout = vgeoms[0];
        }
        else
        {
                /* Collect areas and lines (if any line) */
                gout = GEOSGeom_createCollection(GEOS_GEOMETRYCOLLECTION, vgeoms, nvgeoms);
                if ( ! gout )   /* an exception again */
                {
                        /* cleanup and throw */
                        /* TODO: Shouldn't this be an lwerror ? */
                        lwnotice("GEOSGeom_createCollection() threw an error: %s",
                                 lwgeom_geos_errmsg);
                        /* TODO: cleanup! */
                        return NULL;
                }
        }

        return gout;

}

static GEOSGeometry*
LWGEOM_GEOS_makeValidLine(const GEOSGeometry* gin)
{
        GEOSGeometry* noded;
        noded = LWGEOM_GEOS_nodeLines(gin);
        return noded;
}

static GEOSGeometry*
LWGEOM_GEOS_makeValidMultiLine(const GEOSGeometry* gin)
{
        GEOSGeometry** lines;
        GEOSGeometry** points;
        GEOSGeometry* mline_out=0;
        GEOSGeometry* mpoint_out=0;
        GEOSGeometry* gout=0;
        uint32_t nlines=0, nlines_alloc;
        uint32_t npoints=0;
        uint32_t ngeoms=0, nsubgeoms;
        uint32_t i, j;

        ngeoms = GEOSGetNumGeometries(gin);

        nlines_alloc = ngeoms;
        lines = lwalloc(sizeof(GEOSGeometry*)*nlines_alloc);
        points = lwalloc(sizeof(GEOSGeometry*)*ngeoms);

        for (i=0; i<ngeoms; ++i)
        {
                const GEOSGeometry* g = GEOSGetGeometryN(gin, i);
                GEOSGeometry* vg;
                vg = LWGEOM_GEOS_makeValidLine(g);
                /* Drop any invalid or empty geometry */
                if (!vg)
                        continue;
                if (GEOSisEmpty(vg))
                {
                        GEOSGeom_destroy(vg);
                        continue;
                }
                if ( GEOSGeomTypeId(vg) == GEOS_POINT )
                {
                        points[npoints++] = vg;
                }
                else if ( GEOSGeomTypeId(vg) == GEOS_LINESTRING )
                {
                        lines[nlines++] = vg;
                }
                else if ( GEOSGeomTypeId(vg) == GEOS_MULTILINESTRING )
                {
                        nsubgeoms=GEOSGetNumGeometries(vg);
                        nlines_alloc += nsubgeoms;
                        lines = lwrealloc(lines, sizeof(GEOSGeometry*)*nlines_alloc);
                        for (j=0; j<nsubgeoms; ++j)
                        {
                                const GEOSGeometry* gc = GEOSGetGeometryN(vg, j);
                                /* NOTE: ownership of the cloned geoms will be
                                 *       taken by final collection */
                                lines[nlines++] = GEOSGeom_clone(gc);
                        }
                }
                else
                {
                        /* NOTE: return from GEOSGeomType will leak
                         * but we really don't expect this to happen */
                        lwerror("unexpected geom type returned "
                                "by LWGEOM_GEOS_makeValid: %s",
                                GEOSGeomType(vg));
                }
        }

        if ( npoints )
        {
                if ( npoints > 1 )
                {
                        mpoint_out = GEOSGeom_createCollection(GEOS_MULTIPOINT,
                                                               points, npoints);
                }
                else
                {
                        mpoint_out = points[0];
                }
        }

        if ( nlines )
        {
                if ( nlines > 1 )
                {
                        mline_out = GEOSGeom_createCollection(
                                        GEOS_MULTILINESTRING, lines, nlines);
                }
                else
                {
                        mline_out = lines[0];
                }
        }

        lwfree(lines);

        if ( mline_out && mpoint_out )
        {
                points[0] = mline_out;
                points[1] = mpoint_out;
                gout = GEOSGeom_createCollection(GEOS_GEOMETRYCOLLECTION,
                                                 points, 2);
        }
        else if ( mline_out )
        {
                gout = mline_out;
        }
        else if ( mpoint_out )
        {
                gout = mpoint_out;
        }

        lwfree(points);

        return gout;
}

static GEOSGeometry* LWGEOM_GEOS_makeValid(const GEOSGeometry*);

/*
 * We expect initGEOS being called already.
 * Will return NULL on error (expect error handler being called by then)
 */
static GEOSGeometry*
LWGEOM_GEOS_makeValidCollection(const GEOSGeometry* gin)
{
        int nvgeoms;
        GEOSGeometry **vgeoms;
        GEOSGeom gout;
        unsigned int i;

        nvgeoms = GEOSGetNumGeometries(gin);
        if ( nvgeoms == -1 ) {
                lwerror("GEOSGetNumGeometries: %s", lwgeom_geos_errmsg);
                return 0;
        }

        vgeoms = lwalloc( sizeof(GEOSGeometry*) * nvgeoms );
        if ( ! vgeoms ) {
                lwerror("LWGEOM_GEOS_makeValidCollection: out of memory");
                return 0;
        }

        for ( i=0; i<nvgeoms; ++i ) {
                vgeoms[i] = LWGEOM_GEOS_makeValid( GEOSGetGeometryN(gin, i) );
                if ( ! vgeoms[i] ) {
                        while (i--) GEOSGeom_destroy(vgeoms[i]);
                        lwfree(vgeoms);
                        /* we expect lwerror being called already by makeValid */
                        return NULL;
                }
        }

        /* Collect areas and lines (if any line) */
        gout = GEOSGeom_createCollection(GEOS_GEOMETRYCOLLECTION, vgeoms, nvgeoms);
        if ( ! gout )   /* an exception again */
        {
                /* cleanup and throw */
                for ( i=0; i<nvgeoms; ++i ) GEOSGeom_destroy(vgeoms[i]);
                lwfree(vgeoms);
                lwerror("GEOSGeom_createCollection() threw an error: %s",
                         lwgeom_geos_errmsg);
                return NULL;
        }
        lwfree(vgeoms);

        return gout;

}


static GEOSGeometry*
LWGEOM_GEOS_makeValid(const GEOSGeometry* gin)
{
        GEOSGeometry* gout;
        char ret_char;

        /*
         * Step 2: return what we got so far if already valid
         */

        ret_char = GEOSisValid(gin);
        if ( ret_char == 2 )
        {
                /* I don't think should ever happen */
                lwerror("GEOSisValid(): %s", lwgeom_geos_errmsg);
                return NULL;
        }
        else if ( ret_char )
        {
                LWDEBUGF(3,
                               "Geometry [%s] is valid. ",
                               lwgeom_to_ewkt(GEOS2LWGEOM(gin, 0)));

                /* It's valid at this step, return what we have */
                return GEOSGeom_clone(gin);
        }

        LWDEBUGF(3,
                       "Geometry [%s] is still not valid: %s. "
                       "Will try to clean up further.",
                       lwgeom_to_ewkt(GEOS2LWGEOM(gin, 0)), lwgeom_geos_errmsg);



        /*
         * Step 3 : make what we got valid
         */

        switch (GEOSGeomTypeId(gin))
        {
        case GEOS_MULTIPOINT:
        case GEOS_POINT:
                /* points are always valid, but we might have invalid ordinate values */
                lwnotice("PUNTUAL geometry resulted invalid to GEOS -- dunno how to clean that up");
                return NULL;
                break;

        case GEOS_LINESTRING:
                gout = LWGEOM_GEOS_makeValidLine(gin);
                if ( ! gout )  /* an exception or something */
                {
                        /* cleanup and throw */
                        lwerror("%s", lwgeom_geos_errmsg);
                        return NULL;
                }
                break; /* we've done */

        case GEOS_MULTILINESTRING:
                gout = LWGEOM_GEOS_makeValidMultiLine(gin);
                if ( ! gout )  /* an exception or something */
                {
                        /* cleanup and throw */
                        lwerror("%s", lwgeom_geos_errmsg);
                        return NULL;
                }
                break; /* we've done */

        case GEOS_POLYGON:
        case GEOS_MULTIPOLYGON:
        {
                gout = LWGEOM_GEOS_makeValidPolygon(gin);
                if ( ! gout )  /* an exception or something */
                {
                        /* cleanup and throw */
                        lwerror("%s", lwgeom_geos_errmsg);
                        return NULL;
                }
                break; /* we've done */
        }

        case GEOS_GEOMETRYCOLLECTION:
        {
                gout = LWGEOM_GEOS_makeValidCollection(gin);
                if ( ! gout )  /* an exception or something */
                {
                        /* cleanup and throw */
                        lwerror("%s", lwgeom_geos_errmsg);
                        return NULL;
                }
                break; /* we've done */
        }

        default:
        {
                char* typname = GEOSGeomType(gin);
                lwnotice("ST_MakeValid: doesn't support geometry type: %s",
                         typname);
                GEOSFree(typname);
                return NULL;
                break;
        }
        }

#if PARANOIA_LEVEL > 1
        /*
         * Now check if every point of input is also found
         * in output, or abort by returning NULL
         *
         * Input geometry was lwgeom_in
         */
        {
                        int loss;
                        GEOSGeometry *pi, *po, *pd;

                        /* TODO: handle some errors here...
                         * Lack of exceptions is annoying indeed,
                         * I'm getting old --strk;
                         */
                        pi = GEOSGeom_extractUniquePoints(gin);
                        po = GEOSGeom_extractUniquePoints(gout);
                        pd = GEOSDifference(pi, po); /* input points - output points */
                        GEOSGeom_destroy(pi);
                        GEOSGeom_destroy(po);
                        loss = pd && !GEOSisEmpty(pd);
                        GEOSGeom_destroy(pd);
                        if ( loss )
                        {
                                lwnotice("%s [%d] Vertices lost in LWGEOM_GEOS_makeValid", __FILE__, __LINE__);
                                /* return NULL */
                        }
        }
#endif /* PARANOIA_LEVEL > 1 */


        return gout;
}

/* Exported. Uses GEOS internally */
LWGEOM*
lwgeom_make_valid(LWGEOM* lwgeom_in)
{
        int is3d;
        GEOSGeom geosgeom;
        GEOSGeometry* geosout;
        LWGEOM *lwgeom_out;

        is3d = FLAGS_GET_Z(lwgeom_in->flags);

        /*
         * Step 1 : try to convert to GEOS, if impossible, clean that up first
         *          otherwise (adding only duplicates of existing points)
         */

        initGEOS(lwgeom_geos_error, lwgeom_geos_error);

        lwgeom_out = lwgeom_in;
        geosgeom = LWGEOM2GEOS(lwgeom_out, 0);
        if ( ! geosgeom )
        {
                LWDEBUGF(4,
                               "Original geom can't be converted to GEOS (%s)"
                               " - will try cleaning that up first",
                               lwgeom_geos_errmsg);


                lwgeom_out = lwgeom_make_geos_friendly(lwgeom_out);
                if ( ! lwgeom_out )
                {
                        lwerror("Could not make a valid geometry out of input");
                }

                /* try again as we did cleanup now */
                /* TODO: invoke LWGEOM2GEOS directly with autoclean ? */
                geosgeom = LWGEOM2GEOS(lwgeom_out, 0);
                if ( ! geosgeom )
                {
                        lwerror("Couldn't convert POSTGIS geom to GEOS: %s",
                                lwgeom_geos_errmsg);
                        return NULL;
                }

        }
        else
        {
                LWDEBUG(4, "original geom converted to GEOS");
                lwgeom_out = lwgeom_in;
        }

        geosout = LWGEOM_GEOS_makeValid(geosgeom);
        GEOSGeom_destroy(geosgeom);
        if ( ! geosout )
        {
                return NULL;
        }

        lwgeom_out = GEOS2LWGEOM(geosout, is3d);
        GEOSGeom_destroy(geosout);

        if ( lwgeom_is_collection(lwgeom_in) && ! lwgeom_is_collection(lwgeom_out) )
        {{
                LWGEOM **ogeoms = lwalloc(sizeof(LWGEOM*));
                LWGEOM *ogeom;
                LWDEBUG(3, "lwgeom_make_valid: forcing multi");
                /* NOTE: this is safe because lwgeom_out is surely not lwgeom_in or
                 * otherwise we couldn't have a collection and a non-collection */
                assert(lwgeom_in != lwgeom_out);
                ogeoms[0] = lwgeom_out;
                ogeom = (LWGEOM *)lwcollection_construct(MULTITYPE[lwgeom_out->type],
                                          lwgeom_out->srid, lwgeom_out->bbox, 1, ogeoms);
                lwgeom_out->bbox = NULL;
                lwgeom_out = ogeom;
        }}

        lwgeom_out->srid = lwgeom_in->srid;
        return lwgeom_out;
}