Ensure that QgsGeometry::offsetCurve does not reverse curve orientation

qgis · Nov 9, 2018 · e5946c5 · e5946c5
1 parent d1e09a2
commit e5946c5
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Showing 2 changed files with 30 additions and 2 deletions.
diff --git a/src/core/geometry/qgsgeometry.cpp b/src/core/geometry/qgsgeometry.cpp
@@ -1746,14 +1746,26 @@ QgsGeometry QgsGeometry::offsetCurve( double distance, int segments, JoinStyle j
   {
     QgsGeos geos( d->geometry.get() );
     mLastError.clear();
-    QgsAbstractGeometry *offsetGeom = geos.offsetCurve( distance, segments, joinStyle, miterLimit, &mLastError );
+
+    // GEOS can flip the curve orientation in some circumstances. So record previous orientation and correct if required
+    const QgsCurve::Orientation prevOrientation = qgsgeometry_cast< const QgsCurve * >( d->geometry.get() )->orientation();
+
+    std::unique_ptr< QgsAbstractGeometry > offsetGeom( geos.offsetCurve( distance, segments, joinStyle, miterLimit, &mLastError ) );
     if ( !offsetGeom )
     {
       QgsGeometry result;
       result.mLastError = mLastError;
       return result;
     }
-    return QgsGeometry( offsetGeom );
+
+    const QgsCurve::Orientation newOrientation = qgsgeometry_cast< const QgsCurve * >( offsetGeom.get() )->orientation();
+    if ( newOrientation != prevOrientation )
+    {
+      // GEOS has flipped line orientation, flip it back
+      std::unique_ptr< QgsAbstractGeometry > flipped( qgsgeometry_cast< const QgsCurve * >( offsetGeom.get() )->reversed() );
+      offsetGeom = std::move( flipped );
+    }
+    return QgsGeometry( std::move( offsetGeom ) );
   }
 }
 

diff --git a/tests/src/python/test_qgsgeometry.py b/tests/src/python/test_qgsgeometry.py
@@ -4483,6 +4483,22 @@ def testBoundingBoxIntersectsRectangle(self):
             res = g1.boundingBoxIntersects(t[1])
             self.assertEqual(res, t[2], "mismatch for {} to {}, expected:\n{}\nGot:\n{}\n".format(g1.asWkt(), t[1].toString(), t[2], res))
 
+    def testOffsetCurve(self):
+        tests = [
+            ["LINESTRING (0 0, 0 100, 100 100)", 1, "LineString (-1 0, -1 101, 100 101)"],
+            ["LINESTRING (0 0, 0 100, 100 100)", -1, "LineString (1 0, 1 99, 100 99)"],
+            ["LINESTRING (100 100, 0 100, 0 0)", 1, "LineString (100 99, 1 99, 1 0)"],
+            ["LINESTRING (100 100, 0 100, 0 0)", -1, "LineString (100 101, -1 101, -1 0)"],
+            ["MULTILINESTRING ((0 0, 0 100, 100 100),(100 100, 0 100, 0 0))", 1, "MultiLineString ((-1 0, -1 101, 100 101),(100 99, 1 99, 1 0))"]
+        ]
+        for t in tests:
+            g1 = QgsGeometry.fromWkt(t[0])
+            res = g1.offsetCurve(t[1], 2, QgsGeometry.JoinStyleMiter, 5)
+
+            self.assertEqual(res.asWkt(1), t[2],
+                             "mismatch for {} to {}, expected:\n{}\nGot:\n{}\n".format(t[0], t[1],
+                                                                                       t[2], res.asWkt(1)))
+
     def renderGeometry(self, geom, use_pen, as_polygon=False, as_painter_path=False):
         image = QImage(200, 200, QImage.Format_RGB32)
         image.fill(QColor(0, 0, 0))