Add GEOSSegmentIntersection to CAPI

Closes #873
Closes #101

capi/geos_c.cpp

@@ -1394,4 +1394,15 @@ GEOSVoronoiDiagram(const Geometry *g, const Geometry *env, double tolerance, int
   return GEOSVoronoiDiagram_r(handle, g, env, tolerance, onlyEdges);
 }
 
+int
+GEOSSegmentIntersection(double ax0, double ay0, double ax1, double ay1,
+                        double bx0, double by0, double bx1, double by1,
+                        double* cx, double* cy)
+{
+    return GEOSSegmentIntersection_r(handle,
+        ax0, ay0, ax1, ay1,
+        bx0, by0, bx1, by1,
+        cx, cy);
+}
+
 } /* extern "C" */

capi/geos_c.h.in

@@ -721,6 +721,30 @@ extern GEOSGeometry GEOS_DLL * GEOSVoronoiDiagram_r(
 				double tolerance,
 				int onlyEdges);
 
+/*
+ * Computes the coordinate where two line segments intersect, if any
+ *
+ * @param ax0 x-coordinate of first point in first segment
+ * @param ay0 y-coordinate of first point in first segment
+ * @param ax1 x-coordinate of second point in first segment
+ * @param ay1 y-coordinate of second point in first segment
+ * @param bx0 x-coordinate of first point in second segment
+ * @param by0 y-coordinate of first point in second segment
+ * @param bx1 x-coordinate of second point in second segment
+ * @param by1 y-coordinate of second point in second segment
+ * @param cx x-coordinate of intersection point
+ * @param cy y-coordinate of intersection point
+ *
+ * @return 0 on error, 1 on success, -1 if segments do not intersect
+ */
+
+extern int GEOS_DLL GEOSSegmentIntersection_r(
+       GEOSContextHandle_t extHandle,
+       double ax0, double ay0,
+       double ax1, double ay1,
+       double bx0, double by0,
+       double bx1, double by1,
+       double* cx, double* cy);
 
 /************************************************************************
  *
@@ -1687,6 +1711,29 @@ extern GEOSGeometry GEOS_DLL * GEOSVoronoiDiagram(
                 const GEOSGeometry *env,
                 double tolerance,
                 int onlyEdges);
+/*
+ * Computes the coordinate where two line segments intersect, if any
+ *
+ * @param ax0 x-coordinate of first point in first segment
+ * @param ay0 y-coordinate of first point in first segment
+ * @param ax1 x-coordinate of second point in first segment
+ * @param ay1 y-coordinate of second point in first segment
+ * @param bx0 x-coordinate of first point in second segment
+ * @param by0 y-coordinate of first point in second segment
+ * @param bx1 x-coordinate of second point in second segment
+ * @param by1 y-coordinate of second point in second segment
+ * @param cx x-coordinate of intersection point
+ * @param cy y-coordinate of intersection point
+ *
+ * @return 0 on error, 1 on success, -1 if segments do not intersect
+ */
+
+extern int GEOS_DLL GEOSSegmentIntersection(
+       double ax0, double ay0,
+       double ax1, double ay1,
+       double bx0, double by0,
+       double bx1, double by1,
+       double* cx, double* cy);
 
 /************************************************************************
  *

capi/geos_ts_c.cpp

@@ -17,6 +17,7 @@
  ***********************************************************************/
 
 #include <geos/platform.h>  // for FINITE
+#include <geos/geom/Coordinate.h>
 #include <geos/geom/Geometry.h>
 #include <geos/geom/prep/PreparedGeometry.h>
 #include <geos/geom/prep/PreparedGeometryFactory.h>
@@ -27,6 +28,7 @@
 #include <geos/geom/MultiLineString.h>
 #include <geos/geom/MultiPolygon.h>
 #include <geos/geom/LinearRing.h>
+#include <geos/geom/LineSegment.h>
 #include <geos/geom/LineString.h>
 #include <geos/geom/PrecisionModel.h>
 #include <geos/geom/GeometryFactory.h>
@@ -7132,5 +7134,47 @@ GEOSVoronoiDiagram_r(GEOSContextHandle_t extHandle, const Geometry *g1, const Ge
 	return NULL;
 }
 
+int
+GEOSSegmentIntersection_r(GEOSContextHandle_t extHandle,
+    double ax0, double ay0, double ax1, double ay1,
+    double bx0, double by0, double bx1, double by1,
+    double* cx, double* cy)
+{
+    if ( 0 == extHandle ) return 0;
+
+    GEOSContextHandleInternal_t *handle = 0;
+    handle = reinterpret_cast<GEOSContextHandleInternal_t*>(extHandle);
+    if ( 0 == handle->initialized ) return 0;
+
+    try
+    {
+        geos::geom::LineSegment a(ax0, ay0, ax1, ay1);
+        geos::geom::LineSegment b(bx0, by0, bx1, by1);
+        geos::geom::Coordinate isect;
+
+        bool intersects = a.intersection(b, isect);
+
+        if (!intersects)
+        {
+            return -1;
+        }
+
+        *cx = isect.x;
+        *cy = isect.y;
+
+        return 1;
+    }
+    catch(const std::exception &e)
+    {
+        handle->ERROR_MESSAGE("%s", e.what());
+    }
+    catch(...)
+    {
+        handle->ERROR_MESSAGE("Unknown exception thrown");
+    }
+
+    return 0;
+}
+
 } /* extern "C" */
 

tests/unit/capi/GEOSSegmentIntersectionTest.cpp

@@ -0,0 +1,83 @@
+//
+// Test Suite for C-API GEOSSegmentIntersection
+#include <tut/tut.hpp>
+// geos
+#include <geos_c.h>
+// std
+#include <cstdarg>
+#include <cstdio>
+#include <cstdlib>
+
+namespace tut
+{
+    //
+    // Test Group
+    //
+
+    // Common data used in test cases.
+    struct test_capigeossegmentintersection
+    {
+        static void notice(const char *fmt, ...)
+        {
+            std::fprintf( stdout, "NOTICE: ");
+
+            va_list ap;
+            va_start(ap, fmt);
+            std::vfprintf(stdout, fmt, ap);
+            va_end(ap);
+
+            std::fprintf(stdout, "\n");
+        }
+
+        test_capigeossegmentintersection()
+        {
+            initGEOS(notice, notice);
+        }
+
+        ~test_capigeossegmentintersection()
+        {
+            finishGEOS();
+        }
+    };
+
+    typedef test_group<test_capigeossegmentintersection> group;
+    typedef group::object object;
+
+    group test_capigeossegmentintersection_group("capi::GEOSSegmentIntersection");
+
+    //
+    // Test Cases
+    //
+    template<>
+    template<>
+    void object::test<1>()
+    {
+        // plain old intersection
+        int result;
+        double x,y;
+
+        result = GEOSSegmentIntersection(0, 0, 10, 10,
+                                         8, 0, 8, 10,
+                                         &x, &y);
+
+        ensure_equals(result, 1);
+        ensure_equals(x, 8);
+        ensure_equals(y, 8);
+    }
+
+    template<>
+    template<>
+    void object::test<2>()
+    {
+        // no intersection
+        int result;
+        double x,y;
+
+        result = GEOSSegmentIntersection(0, 0, 10, 10,
+                                         8, 0, 8,  2,
+                                         &x, &y);
+
+        ensure_equals(result, -1);
+    }
+
+} // namespace tut