[Geometry checker] Guard against producing degenerate geometries

Author: manisandro

src/plugins/geometry_checker/checks/qgsgeometryanglecheck.cpp

@@ -114,14 +114,16 @@ void QgsGeometryAngleCheck::fixError( QgsGeometryCheckError* error, int method,
   }
   else if ( method == DeleteNode )
   {
-
-    if ( n <= 3 )
+    if ( !QgsGeometryCheckerUtils::canDeleteVertex( geometry, vidx.part, vidx.ring ) )
     {
       error->setFixFailed( tr( "Resulting geometry is degenerate" ) );
     }
+    else if ( !geometry->deleteVertex( error->vidx() ) )
+    {
+      error->setFixFailed( tr( "Failed to delete vertex" ) );
+    }
     else
     {
-      geometry->deleteVertex( vidx );
       mFeaturePool->updateFeature( feature );
       error->setFixed( method );
       changes[error->featureId()].append( Change( ChangeNode, ChangeRemoved, vidx ) );

src/plugins/geometry_checker/checks/qgsgeometryduplicatenodescheck.cpp

@@ -86,11 +86,14 @@ void QgsGeometryDuplicateNodesCheck::fixError( QgsGeometryCheckError* error, int
   }
   else if ( method == RemoveDuplicates )
   {
-    geom->deleteVertex( error->vidx() );
-    if ( QgsGeometryCheckerUtils::polyLineSize( geom, vidx.part, vidx.ring ) < 3 )
+    if ( !QgsGeometryCheckerUtils::canDeleteVertex( geom, vidx.part, vidx.ring ) )
     {
       error->setFixFailed( tr( "Resulting geometry is degenerate" ) );
     }
+    else if ( !geom->deleteVertex( error->vidx() ) )
+    {
+      error->setFixFailed( tr( "Failed to delete vertex" ) );
+    }
     else
     {
       mFeaturePool->updateFeature( feature );

src/plugins/geometry_checker/utils/qgsgeometrycheckerutils.h

@@ -72,6 +72,14 @@ namespace QgsGeometryCheckerUtils
     return ( dx * dx + dy * dy ) < tol * tol;
   }
 
+  inline bool canDeleteVertex( const QgsAbstractGeometryV2* geom, int iPart, int iRing )
+  {
+    int nVerts = geom->vertexCount( iPart, iRing );
+    QgsPointV2 front = geom->vertexAt( QgsVertexId( iPart, iRing, 0 ) );
+    QgsPointV2 back = geom->vertexAt( QgsVertexId( iPart, iRing, nVerts - 1 ) );
+    bool closed = back == front;
+    return closed ? nVerts > 4 : nVerts > 2;
+  }
 } // QgsGeometryCheckerUtils
 
 #endif // QGS_GEOMETRYCHECKERUTILS_H