Add method to determine orientation of closed curves

qgis · Nov 9, 2018 · c22364d · c22364d
1 parent 6e16651
commit c22364d
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diff --git a/python/core/auto_generated/geometry/qgscurve.sip.in b/python/core/auto_generated/geometry/qgscurve.sip.in
@@ -229,6 +229,23 @@ If a curve isClosed(), it has infinite sinuosity and will return NaN.
 .. versionadded:: 3.2
 %End
 
+    enum Orientation
+    {
+      Clockwise,
+      CounterClockwise,
+    };
+
+    Orientation orientation() const;
+%Docstring
+Returns the curve's orientation, e.g. clockwise or counter-clockwise.
+
+.. warning::
+
+   The result is not predictable for non-closed curves.
+
+.. versionadded:: 3.6
+%End
+
 
 
   protected:

diff --git a/src/core/geometry/qgscurve.cpp b/src/core/geometry/qgscurve.cpp
@@ -214,6 +214,13 @@ double QgsCurve::sinuosity() const
   return length() / d;
 }
 
+QgsCurve::Orientation QgsCurve::orientation() const
+{
+  double a = 0;
+  sumUpArea( a );
+  return a < 0 ? Clockwise : CounterClockwise;
+}
+
 void QgsCurve::clearCache() const
 {
   mBoundingBox = QgsRectangle();

diff --git a/src/core/geometry/qgscurve.h b/src/core/geometry/qgscurve.h
@@ -213,6 +213,22 @@ class CORE_EXPORT QgsCurve: public QgsAbstractGeometry
      */
     double sinuosity() const;
 
+    //! Curve orientation
+    enum Orientation
+    {
+      Clockwise, //!< Clockwise orientation
+      CounterClockwise, //!< Counter-clockwise orientation
+    };
+
+    /**
+     * Returns the curve's orientation, e.g. clockwise or counter-clockwise.
+     *
+     * \warning The result is not predictable for non-closed curves.
+     *
+     * \since QGIS 3.6
+     */
+    Orientation orientation() const;
+
 #ifndef SIP_RUN
 
     /**

diff --git a/tests/src/core/testqgsgeometry.cpp b/tests/src/core/testqgsgeometry.cpp
@@ -2760,6 +2760,13 @@ void TestQgsGeometry::circularString()
   interpolateResult.reset( interpolate.interpolatePoint( 1 ) );
   QCOMPARE( interpolateResult->asWkt( 2 ), QStringLiteral( "Point (10.46 0.84)" ) );
 
+  // orientation
+  QgsCircularString orientation;
+  ( void )orientation.orientation(); // no crash
+  orientation.setPoints( QgsPointSequence() << QgsPoint( 0, 0 ) << QgsPoint( 0, 1 ) << QgsPoint( 1, 1 ) << QgsPoint( 1, 0 ) << QgsPoint( 0, 0 ) );
+  QCOMPARE( orientation.orientation(), QgsCurve::Clockwise );
+  orientation.setPoints( QgsPointSequence() << QgsPoint( 0, 0 ) << QgsPoint( 1, 0 ) << QgsPoint( 1, 1 ) << QgsPoint( 0, 1 ) << QgsPoint( 0, 0 ) );
+  QCOMPARE( orientation.orientation(), QgsCurve::CounterClockwise );
 }
 
 
@@ -4767,6 +4774,14 @@ void TestQgsGeometry::lineString()
   interpolate.setPoints( QgsPointSequence() << QgsPoint( 11, 2 ) << QgsPoint( 11, 12 ) << QgsPoint( 111, 12 ) );
   interpolateResult.reset( interpolate.interpolatePoint( 1 ) );
   QCOMPARE( interpolateResult->asWkt( 2 ), QStringLiteral( "Point (11 3)" ) );
+
+  // orientation
+  QgsLineString orientation;
+  ( void )orientation.orientation(); // no crash
+  orientation.setPoints( QgsPointSequence() << QgsPoint( 0, 0 ) << QgsPoint( 0, 1 ) << QgsPoint( 1, 1 ) << QgsPoint( 1, 0 ) << QgsPoint( 0, 0 ) );
+  QCOMPARE( orientation.orientation(), QgsCurve::Clockwise );
+  orientation.setPoints( QgsPointSequence() << QgsPoint( 0, 0 ) << QgsPoint( 1, 0 ) << QgsPoint( 1, 1 ) << QgsPoint( 0, 1 ) << QgsPoint( 0, 0 ) );
+  QCOMPARE( orientation.orientation(), QgsCurve::CounterClockwise );
 }
 
 void TestQgsGeometry::polygon()
@@ -11449,6 +11464,13 @@ void TestQgsGeometry::compoundCurve()
   interpolateResult.reset( interpolate.interpolatePoint( 1 ) );
   QCOMPARE( interpolateResult->asWkt( 2 ), QStringLiteral( "Point (6 0)" ) );
 
+  // orientation
+  QgsCompoundCurve orientation;
+  ( void )orientation.orientation(); // no crash
+  orientation.fromWkt( QStringLiteral( "CompoundCurve( ( 0 0, 0 1), CircularString (0 1, 1 1, 1 0), (1 0, 0 0))" ) );
+  QCOMPARE( orientation.orientation(), QgsCurve::Clockwise );
+  orientation.fromWkt( QStringLiteral( "CompoundCurve( ( 0 0, 1 0), CircularString (1 0, 1 1, 0 1), (0 1, 0 0))" ) );
+  QCOMPARE( orientation.orientation(), QgsCurve::CounterClockwise );
 }
 
 void TestQgsGeometry::multiPoint()