Structural Repair with GEOS

structural.c

#include <stdio.h>
#include <stdarg.h>

#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);
}


int main()
{
    /* Send notice and error messages to our stdout handler */
    initGEOS(geos_message_handler, geos_message_handler);


    GEOSMakeValidParams* params = GEOSMakeValidParams_create();
    GEOSMakeValidParams_setKeepCollapsed(params, 0);
    GEOSMakeValidParams_setMethod(params, GEOS_MAKE_VALID_STRUCTURE);


    const char* wkt = "MULTIPOLYGON( ((0 0 , 10 0, 10 10, 0 10, 0 0), ( 8 6, 8 8, 12 8, 12 6, 8 6) ),  (( 11 0, 15 0, 15 10, 11 10, 11 0))) "; // hole sticks out over other polygon
    
    /* Read the WKT into geometry objects */
    GEOSWKTReader* reader = GEOSWKTReader_create();
    GEOSGeometry* geom = GEOSWKTReader_read(reader, wkt);

    GEOSGeometry* geom_repaired = GEOSMakeValidWithParams(geom, params);

    
    /* Convert result to WKT */
    GEOSWKTWriter* writer = GEOSWKTWriter_create();
    /* Trim trailing zeros off output */
    GEOSWKTWriter_setTrim(writer, 1);

    /* Print answer */
    
    char* wkt_repaired = GEOSWKTWriter_write(writer, geom_repaired);
    printf("Repaired:         %s\n", wkt_repaired);

    /* Clean up everything we allocated */
    GEOSWKTReader_destroy(reader);
    GEOSWKTWriter_destroy(writer);
    GEOSGeom_destroy(geom);
    GEOSGeom_destroy(geom_repaired);
    GEOSFree(wkt_repaired);

    /* Clean up the global context */
    finishGEOS();

    /* Done */
    return 0;
}