[QGIS Commit] r10935 - trunk/qgis/src/core

[svn_qgis at osgeo.org]

Author: mhugent
Date: 2009-06-16 00:41:18 -0400 (Tue, 16 Jun 2009)
New Revision: 10935

Modified:
   trunk/qgis/src/core/qgsgeometry.cpp
Log:
Replace the hardcoded treshold in line splitting code and added more comment

Modified: trunk/qgis/src/core/qgsgeometry.cpp
===================================================================
--- trunk/qgis/src/core/qgsgeometry.cpp	2009-06-15 17:13:46 UTC (rev 10934)
+++ trunk/qgis/src/core/qgsgeometry.cpp	2009-06-16 04:41:18 UTC (rev 10935)
@@ -4794,9 +4794,12 @@
   QVector<GEOSGeometry*> testedGeometries;
   GEOSGeometry* intersectGeom = 0;
 
-  //hardcoded thresholds
+  //Create a small buffer around the original geometry
+  //and intersect candidate line segments with the buffer.
+  //Then we use the ratio intersection length / segment length to
+  //decide if the line segment belongs to the original geometry or
+  //if it is part of the splitting line
   double bufferDistance = 0.0000001;
-  double intersectThreshold =  0.00001;
 
   for ( int i = 0; i < GEOSGetNumGeometries( mergedLines ); i++ )
   {
@@ -4804,8 +4807,14 @@
     intersectGeom = GEOSIntersection( mGeos, GEOSBuffer( testing, bufferDistance, DEFAULT_QUADRANT_SEGMENTS ) );
     double len;
     GEOSLength( intersectGeom, &len );
-    if ( len > intersectThreshold )
+     double testingLen;
+    GEOSLength( testing, &testingLen);
+    double ratio = len / testingLen;
+    //the ratios for geometries that belong to the original line are usually close to 1
+    if ( ratio >= 0.5 && ratio <= 1.5)
+    {
       testedGeometries << GEOSGeom_clone( testing );
+    }
     GEOSGeom_destroy( intersectGeom );
   }