lwgeom_geos_cluster.c

Go to the documentation of this file.

/**********************************************************************
 *
 * 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 2015-2016 Daniel Baston <dbaston@gmail.com>
 *
 **********************************************************************/
 
#include <string.h>
#include "liblwgeom.h"
#include "liblwgeom_internal.h"
#include "lwgeom_log.h"
#include "lwgeom_geos.h"
#include "lwunionfind.h"
 
static const int STRTREE_NODE_CAPACITY = 10;
 
/* Utility struct used to accumulate items in GEOSSTRtree_query callback */
struct QueryContext
{
        void** items_found;
        uint32_t items_found_size;
        uint32_t num_items_found;
};
 
/* Utility struct to keep GEOSSTRtree and associated structures to be freed after use */
struct STRTree
{
        GEOSSTRtree* tree;
        GEOSGeometry** envelopes;
        uint32_t* geom_ids;
        uint32_t num_geoms;
};
 
static struct STRTree make_strtree(void** geoms, uint32_t num_geoms, char is_lwgeom);
static void destroy_strtree(struct STRTree * tree);
static int combine_geometries(UNIONFIND* uf, void** geoms, uint32_t num_geoms, void*** clustersGeoms, uint32_t* num_clusters, char is_lwgeom);
 
/* Make a minimal GEOSGeometry* whose Envelope covers the same 2D extent as
 * the supplied GBOX.  This is faster and uses less memory than building a
 * five-point polygon with GBOX2GEOS.
 */
static GEOSGeometry*
geos_envelope_surrogate(const LWGEOM* g)
{
        if (lwgeom_is_empty(g))
                return GEOSGeom_createEmptyPolygon();
 
        if (lwgeom_get_type(g) == POINTTYPE) {
                const POINT2D* pt = getPoint2d_cp(lwgeom_as_lwpoint(g)->point, 0);
                return make_geos_point(pt->x, pt->y);
        } else {
                const GBOX* box = lwgeom_get_bbox(g);
                if (!box)
                        return NULL;
 
                return make_geos_segment(box->xmin, box->ymin, box->xmax, box->ymax);
        }
}
 
static struct STRTree
make_strtree(void** geoms, uint32_t num_geoms, char is_lwgeom)
{
        struct STRTree tree;
        tree.envelopes = 0;
        tree.num_geoms = 0;
        tree.geom_ids = 0;
 
        tree.tree = GEOSSTRtree_create(STRTREE_NODE_CAPACITY);
        if (tree.tree == NULL)
        {
                return tree;
        }
        tree.geom_ids  = lwalloc(num_geoms * sizeof(uint32_t));
        tree.num_geoms = num_geoms;
 
        if (is_lwgeom)
        {
                uint32_t i;
                tree.envelopes = lwalloc(num_geoms * sizeof(GEOSGeometry*));
                for (i = 0; i < num_geoms; i++)
                {
                        tree.geom_ids[i] = i;
                        tree.envelopes[i] = geos_envelope_surrogate(geoms[i]);
                        GEOSSTRtree_insert(tree.tree, tree.envelopes[i], &(tree.geom_ids[i]));
                }
        }
        else
        {
                uint32_t i;
                tree.envelopes = NULL;
                for (i = 0; i < num_geoms; i++)
                {
                        tree.geom_ids[i] = i;
                        GEOSSTRtree_insert(tree.tree, geoms[i], &(tree.geom_ids[i]));
                }
        }
 
        return tree;
}
 
static void
destroy_strtree(struct STRTree * tree)
{
        size_t i;
        GEOSSTRtree_destroy(tree->tree);
 
        if (tree->envelopes)
        {
                for (i = 0; i < tree->num_geoms; i++)
                {
                        GEOSGeom_destroy(tree->envelopes[i]);
                }
                lwfree(tree->envelopes);
        }
        lwfree(tree->geom_ids);
}
 
static void
query_accumulate(void* item, void* userdata)
{
        struct QueryContext *cxt = userdata;
        if (!cxt->items_found)
        {
                cxt->items_found_size = 8;
                cxt->items_found = lwalloc(cxt->items_found_size * sizeof(void*));
        }
 
        if (cxt->num_items_found >= cxt->items_found_size)
        {
                cxt->items_found_size = 2 * cxt->items_found_size;
                cxt->items_found = lwrealloc(cxt->items_found, cxt->items_found_size * sizeof(void*));
        }
        cxt->items_found[cxt->num_items_found++] = item;
}
 
/* Identify intersecting geometries and mark them as being in the same set */
int
union_intersecting_pairs(GEOSGeometry** geoms, uint32_t num_geoms, UNIONFIND* uf)
{
        uint32_t p, i;
        struct STRTree tree;
        struct QueryContext cxt =
        {
                .items_found = NULL,
                .num_items_found = 0,
                .items_found_size = 0
        };
        int success = LW_SUCCESS;
 
        if (num_geoms <= 1)
                return LW_SUCCESS;
 
        tree = make_strtree((void**) geoms, num_geoms, LW_FALSE);
        if (tree.tree == NULL)
        {
                destroy_strtree(&tree);
                return LW_FAILURE;
        }
 
        for (p = 0; p < num_geoms; p++)
        {
                const GEOSPreparedGeometry* prep = NULL;
 
                if (!geoms[p] || GEOSisEmpty(geoms[p]))
                        continue;
 
                cxt.num_items_found = 0;
                GEOSSTRtree_query(tree.tree, geoms[p], &query_accumulate, &cxt);
 
                for (i = 0; i < cxt.num_items_found; i++)
                {
                        uint32_t q = *((uint32_t*) cxt.items_found[i]);
 
                        if (p != q && UF_find(uf, p) != UF_find(uf, q))
                        {
                                int geos_type = GEOSGeomTypeId(geoms[p]);
                                int geos_result;
 
                                /* Don't build prepared a geometry around a Point or MultiPoint -
                                 * there are some problems in the implementation, and it's not clear
                                 * there would be a performance benefit in any case.  (See #3433)
                                 */
                                if (geos_type != GEOS_POINT && geos_type != GEOS_MULTIPOINT)
                                {
                                        /* Lazy initialize prepared geometry */
                                        if (prep == NULL)
                                        {
                                                prep = GEOSPrepare(geoms[p]);
                                        }
                                        geos_result = GEOSPreparedIntersects(prep, geoms[q]);
                                }
                                else
                                {
                                        geos_result = GEOSIntersects(geoms[p], geoms[q]);
                                }
                                if (geos_result > 1)
                                {
                                        success = LW_FAILURE;
                                        break;
                                }
                                else if (geos_result)
                                {
                                        UF_union(uf, p, q);
                                }
                        }
                }
 
                if (prep)
                        GEOSPreparedGeom_destroy(prep);
 
                if (!success)
                        break;
        }
 
        if (cxt.items_found)
                lwfree(cxt.items_found);
 
        destroy_strtree(&tree);
        return success;
}
 
int
cluster_intersecting(GEOSGeometry** geoms, uint32_t num_geoms, GEOSGeometry*** clusterGeoms, uint32_t* num_clusters)
{
        int cluster_success;
        UNIONFIND* uf = UF_create(num_geoms);
 
        if (union_intersecting_pairs(geoms, num_geoms, uf) == LW_FAILURE)
        {
                UF_destroy(uf);
                return LW_FAILURE;
        }
 
        cluster_success = combine_geometries(uf, (void**) geoms, num_geoms, (void***) clusterGeoms, num_clusters, 0);
        UF_destroy(uf);
        return cluster_success;
}
 
static int
dbscan_update_context(GEOSSTRtree* tree, struct QueryContext* cxt, LWGEOM** geoms, uint32_t p, double eps)
{
        cxt->num_items_found = 0;
 
        GEOSGeometry* query_envelope;
 
        LW_ON_INTERRUPT(return LW_FAILURE);
 
        if (geoms[p]->type == POINTTYPE)
        {
                const POINT2D* pt = getPoint2d_cp(lwgeom_as_lwpoint(geoms[p])->point, 0);
                query_envelope = make_geos_segment( pt->x - eps, pt->y - eps, pt->x + eps, pt->y + eps );
        } else {
                const GBOX* box = lwgeom_get_bbox(geoms[p]);
                query_envelope = make_geos_segment( box->xmin - eps, box->ymin - eps, box->xmax + eps, box->ymax + eps );
        }
 
        if (!query_envelope)
                return LW_FAILURE;
 
        GEOSSTRtree_query(tree, query_envelope, &query_accumulate, cxt);
 
        GEOSGeom_destroy(query_envelope);
 
        return LW_SUCCESS;
}
 
/* Union p's cluster with q's cluster, if q is not a border point of another cluster.
 * Applicable to DBSCAN with minpoints > 1.
 */
static void
union_if_available(UNIONFIND* uf, uint32_t p, uint32_t q, char* is_in_core, char* in_a_cluster)
{
        if (in_a_cluster[q])
        {
                /* Can we merge p's cluster with q's cluster?  We can do this only
                 * if both p and q are considered _core_ points of their respective
                 * clusters.
                 */
                 if (is_in_core[q])
                 {
                         UF_union(uf, p, q);
                 }
        }
        else
        {
                UF_union(uf, p, q);
                in_a_cluster[q] = LW_TRUE;
        }
}
 
/* An optimized DBSCAN union for the case where min_points == 1.
 * If min_points == 1, then we don't care how many neighbors we find; we can union clusters
 * on the fly, as we go through the distance calculations.  This potentially allows us
 * to avoid some distance computations altogether.
 */
static int
union_dbscan_minpoints_1(LWGEOM** geoms, uint32_t num_geoms, UNIONFIND* uf, double eps, char** in_a_cluster_ret)
{
        uint32_t p, i;
        struct STRTree tree;
        struct QueryContext cxt =
        {
                .items_found = NULL,
                .num_items_found = 0,
                .items_found_size = 0
        };
        int success = LW_SUCCESS;
 
        if (in_a_cluster_ret)
        {
                char* in_a_cluster = lwalloc(num_geoms * sizeof(char));
                for (i = 0; i < num_geoms; i++)
                        in_a_cluster[i] = LW_TRUE;
                *in_a_cluster_ret = in_a_cluster;
        }
 
        if (num_geoms <= 1)
                return LW_SUCCESS;
 
        tree = make_strtree((void**) geoms, num_geoms, LW_TRUE);
        if (tree.tree == NULL)
        {
                destroy_strtree(&tree);
                return LW_FAILURE;
        }
 
        for (p = 0; p < num_geoms; p++)
        {
                int rv = LW_SUCCESS;
                if (lwgeom_is_empty(geoms[p]))
                        continue;
 
                rv = dbscan_update_context(tree.tree, &cxt, geoms, p, eps);
                if (rv == LW_FAILURE)
                {
                        destroy_strtree(&tree);
                        return LW_FAILURE;
                }
                for (i = 0; i < cxt.num_items_found; i++)
                {
                        uint32_t q = *((uint32_t*) cxt.items_found[i]);
 
                        if (UF_find(uf, p) != UF_find(uf, q))
                        {
                                double mindist = lwgeom_mindistance2d_tolerance(geoms[p], geoms[q], eps);
                                if (mindist == FLT_MAX)
                                {
                                        success = LW_FAILURE;
                                        break;
                                }
 
                                if (mindist <= eps)
                                        UF_union(uf, p, q);
                        }
                }
        }
 
        if (cxt.items_found)
                lwfree(cxt.items_found);
 
        destroy_strtree(&tree);
 
        return success;
}
 
static int
union_dbscan_general(LWGEOM** geoms, uint32_t num_geoms, UNIONFIND* uf, double eps, uint32_t min_points, char** in_a_cluster_ret)
{
        uint32_t p, i;
        struct STRTree tree;
        struct QueryContext cxt =
        {
                .items_found = NULL,
                .num_items_found = 0,
                .items_found_size = 0
        };
        int success = LW_SUCCESS;
        uint32_t* neighbors;
        char* in_a_cluster;
        char* is_in_core;
 
        in_a_cluster = lwalloc(num_geoms * sizeof(char));
        memset(in_a_cluster, 0, num_geoms * sizeof(char));
 
        if (in_a_cluster_ret)
                *in_a_cluster_ret = in_a_cluster;
 
        /* Bail if we don't even have enough inputs to make a cluster. */
        if (num_geoms < min_points)
        {
                if (!in_a_cluster_ret)
                        lwfree(in_a_cluster);
                return LW_SUCCESS;
        }
 
        tree = make_strtree((void**) geoms, num_geoms, LW_TRUE);
        if (tree.tree == NULL)
        {
                destroy_strtree(&tree);
                return LW_FAILURE;
        }
 
        is_in_core = lwalloc(num_geoms * sizeof(char));
        memset(is_in_core, 0, num_geoms * sizeof(char));
        neighbors = lwalloc(min_points * sizeof(uint32_t));
 
        for (p = 0; p < num_geoms; p++)
        {
                uint32_t num_neighbors = 0;
                int rv;
 
                if (lwgeom_is_empty(geoms[p]))
                        continue;
 
                rv = dbscan_update_context(tree.tree, &cxt, geoms, p, eps);
                if (rv == LW_FAILURE)
                {
                        destroy_strtree(&tree);
                        return LW_FAILURE;
                }
 
                /* We didn't find enough points to do anything, even if they are all within eps. */
                if (cxt.num_items_found < min_points)
                        continue;
 
                for (i = 0; i < cxt.num_items_found; i++)
                {
                        uint32_t q = *((uint32_t*) cxt.items_found[i]);
 
                        if (num_neighbors >= min_points)
                        {
                                /* If we've already identified p as a core point, and it's already
                                 * in the same cluster in q, then there's nothing to learn by
                                 * computing the distance.
                                 */
                                if (UF_find(uf, p) == UF_find(uf, q))
                                        continue;
 
                                /* Similarly, if q is already identified as a border point of another
                                 * cluster, there's no point figuring out what the distance is.
                                 */
                                if (in_a_cluster[q] && !is_in_core[q])
                                        continue;
                        }
 
                        double mindist = lwgeom_mindistance2d_tolerance(geoms[p], geoms[q], eps);
                        if (mindist == FLT_MAX)
                        {
                                success = LW_FAILURE;
                                break;
                        }
 
                        if (mindist <= eps)
                        {
                                /* If we haven't hit min_points yet, we don't know if we can union p and q.
                                 * Just set q aside for now.
                                 */
                                if (num_neighbors < min_points)
                                {
                                        neighbors[num_neighbors++] = q;
 
                                        /* If we just hit min_points, we can now union all of the neighbor geometries
                                         * we've been saving.
                                         */
                                        if (num_neighbors == min_points)
                                        {
                                                uint32_t j;
                                                is_in_core[p] = LW_TRUE;
                                                in_a_cluster[p] = LW_TRUE;
                                                for (j = 0; j < num_neighbors; j++)
                                                {
                                                        union_if_available(uf, p, neighbors[j], is_in_core, in_a_cluster);
                                                }
                                        }
                                }
                                else
                                {
                                        /* If we're above min_points, no need to store our neighbors, just go ahead
                                         * and union them now.  This may allow us to cut out some distance
                                         * computations.
                                         */
                                        union_if_available(uf, p, q, is_in_core, in_a_cluster);
                                }
                        }
                }
 
                if (!success)
                        break;
        }
 
        lwfree(neighbors);
        lwfree(is_in_core);
 
        /* Free in_a_cluster if we're not giving it to our caller */
        if (!in_a_cluster_ret)
                lwfree(in_a_cluster);
 
        if (cxt.items_found)
                lwfree(cxt.items_found);
 
        destroy_strtree(&tree);
        return success;
}
 
int union_dbscan(LWGEOM** geoms, uint32_t num_geoms, UNIONFIND* uf, double eps, uint32_t min_points, char** in_a_cluster_ret)
{
        if (min_points <= 1)
                return union_dbscan_minpoints_1(geoms, num_geoms, uf, eps, in_a_cluster_ret);
        else
                return union_dbscan_general(geoms, num_geoms, uf, eps, min_points, in_a_cluster_ret);
}
 
int
cluster_within_distance(LWGEOM** geoms, uint32_t num_geoms, double tolerance, LWGEOM*** clusterGeoms, uint32_t* num_clusters)
{
        int cluster_success;
        UNIONFIND* uf = UF_create(num_geoms);
 
        if (union_dbscan(geoms, num_geoms, uf, tolerance, 1, NULL) == LW_FAILURE)
        {
                UF_destroy(uf);
                return LW_FAILURE;
        }
 
        cluster_success = combine_geometries(uf, (void**) geoms, num_geoms, (void***) clusterGeoms, num_clusters, 1);
        UF_destroy(uf);
        return cluster_success;
}
 
static int
combine_geometries(UNIONFIND* uf, void** geoms, uint32_t num_geoms, void*** clusterGeoms, uint32_t* num_clusters, char is_lwgeom)
{
        size_t i, j, k;
 
        /* Combine components of each cluster into their own GeometryCollection */
        *num_clusters = uf->num_clusters;
        *clusterGeoms = lwalloc(*num_clusters * sizeof(void*));
 
        void** geoms_in_cluster = lwalloc(num_geoms * sizeof(void*));
        uint32_t* ordered_components = UF_ordered_by_cluster(uf);
        for (i = 0, j = 0, k = 0; i < num_geoms; i++)
        {
                geoms_in_cluster[j++] = geoms[ordered_components[i]];
 
                /* Is this the last geometry in the component? */
                if ((i == num_geoms - 1) ||
                        (UF_find(uf, ordered_components[i]) != UF_find(uf, ordered_components[i+1])))
                {
                        if (k >= uf->num_clusters) {
                                /* Should not get here - it means that we have more clusters than uf->num_clusters thinks we should. */
                                return LW_FAILURE;
                        }
 
                        if (is_lwgeom)
                        {
                                LWGEOM** components = lwalloc(j * sizeof(LWGEOM*));
                                memcpy(components, geoms_in_cluster, j * sizeof(LWGEOM*));
                                (*clusterGeoms)[k++] = lwcollection_construct(COLLECTIONTYPE, components[0]->srid, NULL, j, (LWGEOM**) components);
                        }
                        else
                        {
                                int srid = GEOSGetSRID(((GEOSGeometry**) geoms_in_cluster)[0]);
                                GEOSGeometry* combined = GEOSGeom_createCollection(GEOS_GEOMETRYCOLLECTION, (GEOSGeometry**) geoms_in_cluster, j);
                                GEOSSetSRID(combined, srid);
                                (*clusterGeoms)[k++] = combined;
                        }
                        j = 0;
                }
        }
 
        lwfree(geoms_in_cluster);
        lwfree(ordered_components);
 
        return LW_SUCCESS;
}