[geos-commits] [SCM] GEOS branch main updated. f30852fdfd87e77e2cc13dc8e48a5b308a81f14b
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commit f30852fdfd87e77e2cc13dc8e48a5b308a81f14b
Author: Paul Ramsey <pramsey at cleverelephant.ca>
Date: Thu Jun 8 13:47:10 2023 -0700
Add another example program, showing spatial index and user data
diff --git a/examples/capi_indexed_predicate.c b/examples/capi_indexed_predicate.c
new file mode 100644
index 000000000..26d9fffe6
--- /dev/null
+++ b/examples/capi_indexed_predicate.c
@@ -0,0 +1,219 @@
+/*
+* # GEOS C API example 4
+*
+* Build a spatial index and search it for all points
+* completely contained in arbitrary query polygon.
+*
+* cc -I/usr/local/include capi_indexed_predicate.c -o capi_indexed_predicate -L/usr/local/lib -lgeos_c
+*/
+
+/* System headers */
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <math.h>
+#include <time.h>
+
+/* Only the CAPI header is required */
+#include <geos_c.h>
+
+/*
+* GEOS requires two message handlers to return
+* error and notice message to the calling program.
+*
+* typedef void(* GEOSMessageHandler) (const char *fmt,...)
+*
+* Here we stub out an example that just prints the
+* messages to stdout.
+*/
+static void
+geos_message_handler(const char* fmt, ...)
+{
+ va_list ap;
+ va_start(ap, fmt);
+ vprintf (fmt, ap);
+ va_end(ap);
+}
+
+/*
+* An application will want to index items, which have
+* some attributes and a geometry part.
+*/
+typedef struct
+{
+ GEOSGeometry* geom;
+ size_t id;
+} item_t;
+
+/*
+* A user data struct to pass to the index callback function
+*/
+typedef struct
+{
+ const GEOSPreparedGeometry* prepgeom;
+ item_t** items;
+ size_t nItems;
+ size_t szItems;
+} userdata_t;
+
+/*
+* Userdata both holds our output list of found items and
+* our input PreparedGeometry for fast spatial tests.
+*/
+userdata_t *
+userdata_init(GEOSGeometry* geom)
+{
+ userdata_t* ud = malloc(sizeof(userdata_t));
+ ud->prepgeom = GEOSPrepare(geom);
+ ud->nItems = 0;
+ ud->szItems = 16;
+ ud->items = malloc(sizeof(item_t*) * ud->szItems);
+ return ud;
+}
+
+/*
+* Free the items list and the PreparedGeometry
+*/
+void
+userdata_free(userdata_t* ud)
+{
+ GEOSPreparedGeom_destroy(ud->prepgeom);
+ free(ud->items);
+ free(ud);
+}
+
+
+/*
+* Generate a random item with a location in the range of
+* POINT(0..range, 0..range). Caller must free.
+*/
+static item_t *
+item_random(double range)
+{
+ item_t* item = malloc(sizeof(item_t));
+ double x = range * rand() / RAND_MAX;
+ double y = range * rand() / RAND_MAX;
+ /* Make a point in the point grid */
+ item->geom = GEOSGeom_createPointFromXY(x, y);
+ item->id = rand();
+ return item;
+}
+
+/*
+* Free an item and its geometry.
+*/
+void
+item_free(item_t* item)
+{
+ if (item && item->geom) GEOSGeom_destroy(item->geom);
+ if (item) free(item);
+}
+
+/*
+* Utility function to write out contents of item
+*/
+void
+item_print(const item_t* item)
+{
+ double x, y;
+ GEOSGeomGetX(item->geom, &x);
+ GEOSGeomGetY(item->geom, &y);
+ printf("item %10zu (%g, %g)\n", item->id, x, y);
+}
+
+/*
+* Item query callback for GEOSSTRtree_query()
+*/
+void
+itemQueryCallback(void* item, void* userdata)
+{
+ userdata_t* ud = (userdata_t*)userdata;
+ item_t* indexitem = (item_t*)item;
+ if (GEOSPreparedIntersects(ud->prepgeom, indexitem->geom)) {
+ if (ud->nItems == ud->szItems) {
+ ud->szItems *= 2;
+ ud->items = realloc(ud->items, sizeof(item_t*) * ud->szItems);
+ }
+ ud->items[ud->nItems++] = indexitem;
+ }
+ return;
+}
+
+
+int main()
+{
+ /* Send notice and error messages to our stdout handler */
+ initGEOS(geos_message_handler, geos_message_handler);
+
+ /* How many random items to add to our index */
+ const size_t nItems = 10000;
+ /* The coordinate range of the random locations (0->100.0) */
+ const double range = 100.0;
+ /* Set the seed for rand() */
+ srand(time(NULL));
+
+ /*
+ * The tree doesn't take ownership of inputs, it just
+ * holds pointers, so we keep a list of allocated items
+ * handy in an array for future clean-up
+ */
+ item_t* items[nItems];
+ /*
+ * The create parameter for the tree is not the
+ * number of inputs, it is the number of entries
+ * per node. 10 is a good default number to use.
+ */
+ GEOSSTRtree* tree = GEOSSTRtree_create(10);
+ for (size_t i = 0; i < nItems; i++) {
+ /* Make a random point */
+ item_t* item = item_random(range);
+ /* Store away a reference so we can free it after */
+ items[i] = item;
+ /* Add an entry for it to the tree */
+ GEOSSTRtree_insert(tree, item->geom, item);
+ }
+
+ /* Prepare to read geometries in as text */
+ GEOSWKTReader* reader = GEOSWKTReader_create();
+
+ /* Set up a query rectangle for index query */
+ const char* wkt_bounds = "POLYGON((20 20, 20 24, 24 24, 24 23, 21 23, 21 21, 24 21, 24 20, 20 20))";
+ GEOSGeometry* geom_query = GEOSWKTReader_read(reader, wkt_bounds);
+
+ /* Set up the prepared geometry for the exact tests */
+ userdata_t* ud = userdata_init(geom_query);
+
+ /* Find all items that touch the bounds */
+ /* For non-rectangular query geometry, this will be an over-determined set */
+ GEOSSTRtree_query(
+ tree, // STRTree to query
+ geom_query, // GEOSGeometry query bounds
+ itemQueryCallback, // Callback to process index entries that pass query
+ ud); // Userdata to hand to the callback
+
+ /* Print out the items we found */
+ printf("Found %zu items in the polygon: %s\n", ud->nItems, wkt_bounds);
+ for (size_t i = 0; i < ud->nItems; i++) {
+ item_print(ud->items[i]);
+ }
+
+ /* Done with the found items and prepared geometry now */
+ userdata_free(ud);
+
+ /* Free the query bounds geometry */
+ GEOSGeom_destroy(geom_query);
+
+ /* Freeing the tree does not free the tree inputs */
+ GEOSSTRtree_destroy(tree);
+
+ /* Free all the items in our random item list */
+ for (size_t i = 0; i < nItems; i++) {
+ item_free(items[i]);
+ }
+
+ /* Clean up the global context */
+ finishGEOS();
+
+ /* Done */
+ return 0;
+}
-----------------------------------------------------------------------
Summary of changes:
.../{capi_strtree.c => capi_indexed_predicate.c} | 134 ++++++++++++---------
1 file changed, 78 insertions(+), 56 deletions(-)
copy examples/{capi_strtree.c => capi_indexed_predicate.c} (59%)
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