Add left of line test to QgsLineSegment2D

python/core/geometry/qgslinesegment.sip.in

@@ -162,6 +162,19 @@ Sets the segment's ``end`` point.
 .. seealso:: :py:func:`setEndY`
 
 .. seealso:: :py:func:`setStart`
+%End
+
+    int pointLeftOfLine( const QgsPointXY &point ) const;
+%Docstring
+Tests if a ``point`` is to the left of the line segment.
+
+Returns -1 if the point falls to the left of the line, or +1 if the point
+is to the right.
+
+If the return value is 0, then the test was unsuccessful (e.g. due to testing a point exactly
+on the line, or exactly in line with the segment) and the result is undefined.
+
+.. seealso:: :py:func:`QgsGeometryUtils.leftOfLine`
 %End
 
     bool operator==( const QgsLineSegment2D &other ) const;

src/core/CMakeLists.txt

@@ -463,6 +463,7 @@ SET(QGIS_CORE_SRCS
   geometry/qgsgeometryutils.cpp
   geometry/qgsgeos.cpp
   geometry/qgsinternalgeometryengine.cpp
+  geometry/qgslinesegment.cpp
   geometry/qgslinestring.cpp
   geometry/qgsmulticurve.cpp
   geometry/qgsmultilinestring.cpp

src/core/geometry/qgslinesegment.cpp

@@ -0,0 +1,16 @@
+/***************************************************************************
+                         qgslinesegment.cpp
+                         -----------------
+    begin                : April 2018
+    copyright            : (C) 2018 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************/
+
+#include "qgslinesegment.h"
+#include "qgsgeometryutils.h"
+
+int QgsLineSegment2D::pointLeftOfLine( const QgsPointXY &point ) const
+{
+  return QgsGeometryUtils::leftOfLine( point.x(), point.y(), mStart.x(), mStart.y(), mEnd.x(), mEnd.y() );
+}
+

src/core/geometry/qgslinesegment.h

@@ -176,6 +176,19 @@ class CORE_EXPORT QgsLineSegment2D
       mEnd = end;
     }
 
+    /**
+     * Tests if a \a point is to the left of the line segment.
+     *
+     * Returns -1 if the point falls to the left of the line, or +1 if the point
+     * is to the right.
+     *
+     * If the return value is 0, then the test was unsuccessful (e.g. due to testing a point exactly
+     * on the line, or exactly in line with the segment) and the result is undefined.
+     *
+     * \see QgsGeometryUtils::leftOfLine()
+     */
+    int pointLeftOfLine( const QgsPointXY &point ) const;
+
     //! Equality operator
     bool operator==( const QgsLineSegment2D &other ) const
     {

tests/src/python/test_qgslinesegment.py

@@ -102,6 +102,16 @@ def testLength(self):
         self.assertAlmostEqual(segment.length(), 3.60555127546, 5)
         self.assertEqual(segment.lengthSquared(), 13)
 
+    def testPointLeftOfLine(self):
+        segment = QgsLineSegment2D(QgsPointXY(1, 2), QgsPointXY(3, 5))
+        self.assertEqual(segment.pointLeftOfLine(QgsPointXY(1.5, 6)), -1)
+        self.assertEqual(segment.pointLeftOfLine(QgsPointXY(1.5, -6)), 1)
+        self.assertEqual(segment.pointLeftOfLine(QgsPointXY(5, 8)), 0)
+        segment = QgsLineSegment2D(QgsPointXY(3, 5), QgsPointXY(1, 2))
+        self.assertEqual(segment.pointLeftOfLine(QgsPointXY(1.5, 6)), 1)
+        self.assertEqual(segment.pointLeftOfLine(QgsPointXY(1.5, -6)), -1)
+        self.assertEqual(segment.pointLeftOfLine(QgsPointXY(5, 8)), 0)
+
 
 if __name__ == '__main__':
     unittest.main()