Add geometry methods for calculating the distance to a specified

vertex from the start of the geometry

Author: nyalldawson

python/core/geometry/qgsgeometry.sip

@@ -184,6 +184,14 @@ class QgsGeometry
     //TODO QGIS 3.0 - rename beforeVertex to previousVertex, afterVertex to nextVertex
     QgsPoint closestVertex( const QgsPoint& point, int& atVertex /Out/, int& beforeVertex /Out/, int& afterVertex /Out/, double& sqrDist /Out/ ) const;
 
+    /**
+     * Returns the distance along this geometry from its first vertex to the specified vertex.
+     * @param vertex vertex index to calculate distance to
+     * @returns distance to vertex (following geometry), or -1 for invalid vertex numbers
+     * @note added in QGIS 2.16
+     */
+    double distanceToVertex( int vertex ) const;
+
     /**
      * Returns the indexes of the vertices before and after the given vertex index.
      *

src/core/geometry/qgsgeometry.cpp

@@ -361,6 +361,22 @@ QgsPoint QgsGeometry::closestVertex( const QgsPoint& point, int& atVertex, int&
   return QgsPoint( vp.x(), vp.y() );
 }
 
+double QgsGeometry::distanceToVertex( int vertex ) const
+{
+  if ( !d->geometry )
+  {
+    return -1;
+  }
+
+  QgsVertexId id;
+  if ( !vertexIdFromVertexNr( vertex, id ) )
+  {
+    return -1;
+  }
+
+  return QgsGeometryUtils::distanceToVertex( *( d->geometry ), id );
+}
+
 void QgsGeometry::adjacentVertices( int atVertex, int& beforeVertex, int& afterVertex ) const
 {
   if ( !d->geometry )

src/core/geometry/qgsgeometry.h

@@ -226,6 +226,14 @@ class CORE_EXPORT QgsGeometry
     //TODO QGIS 3.0 - rename beforeVertex to previousVertex, afterVertex to nextVertex
     QgsPoint closestVertex( const QgsPoint& point, int& atVertex, int& beforeVertex, int& afterVertex, double& sqrDist ) const;
 
+    /**
+     * Returns the distance along this geometry from its first vertex to the specified vertex.
+     * @param vertex vertex index to calculate distance to
+     * @returns distance to vertex (following geometry), or -1 for invalid vertex numbers
+     * @note added in QGIS 2.16
+     */
+    double distanceToVertex( int vertex ) const;
+
     /**
      * Returns the indexes of the vertices before and after the given vertex index.
      *

src/core/geometry/qgsgeometryutils.cpp

@@ -89,6 +89,35 @@ QgsPointV2 QgsGeometryUtils::closestVertex( const QgsAbstractGeometryV2& geom, c
   return minDistPoint;
 }
 
+double QgsGeometryUtils::distanceToVertex( const QgsAbstractGeometryV2 &geom, const QgsVertexId &id )
+{
+  double currentDist = 0;
+  QgsVertexId vertexId;
+  QgsPointV2 vertex;
+  QgsPointV2 previousVertex;
+
+  bool first = true;
+  while ( geom.nextVertex( vertexId, vertex ) )
+  {
+    if ( !first )
+    {
+      currentDist += sqrt( QgsGeometryUtils::sqrDistance2D( previousVertex, vertex ) );
+    }
+
+    previousVertex = vertex;
+    first = false;
+
+    if ( vertexId == id )
+    {
+      //found target vertex
+      return currentDist;
+    }
+  }
+
+  //could not find target vertex
+  return -1;
+}
+
 void QgsGeometryUtils::adjacentVertices( const QgsAbstractGeometryV2& geom, QgsVertexId atVertex, QgsVertexId& beforeVertex, QgsVertexId& afterVertex )
 {
   bool polygonType = ( geom.dimension()  == 2 );

src/core/geometry/qgsgeometryutils.h

@@ -41,6 +41,14 @@ class CORE_EXPORT QgsGeometryUtils
      */
     static QgsPointV2 closestVertex( const QgsAbstractGeometryV2& geom, const QgsPointV2& pt, QgsVertexId& id );
 
+    /** Returns the distance along a geometry from its first vertex to the specified vertex.
+     * @param geom geometry
+     * @param id vertex id to find distance to
+     * @returns distance to vertex (following geometry)
+     * @note added in QGIS 2.16
+     */
+    static double distanceToVertex( const QgsAbstractGeometryV2& geom, const QgsVertexId& id );
+
     /** Returns vertices adjacent to a specified vertex within a geometry.
      */
     static void adjacentVertices( const QgsAbstractGeometryV2& geom, QgsVertexId atVertex, QgsVertexId& beforeVertex, QgsVertexId& afterVertex );

tests/src/core/testqgsgeometryutils.cpp

@@ -43,6 +43,7 @@ class TestQgsGeometryUtils: public QObject
     void testLinePerpendicularAngle();
     void testAverageAngle_data();
     void testAverageAngle();
+    void testDistanceToVertex();
 };
 
 
@@ -330,6 +331,36 @@ void TestQgsGeometryUtils::testAverageAngle()
   QVERIFY( qgsDoubleNear( averageAngle, expected, 0.0000000001 ) );
 }
 
+void TestQgsGeometryUtils::testDistanceToVertex()
+{
+  //test with linestring
+  QgsLineStringV2* outerRing1 = new QgsLineStringV2();
+  outerRing1->setPoints( QList<QgsPointV2>() << QgsPointV2( 1, 1 ) << QgsPointV2( 1, 2 ) << QgsPointV2( 2, 2 ) << QgsPointV2( 2, 1 ) << QgsPointV2( 1, 1 ) );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( *outerRing1, QgsVertexId( 0, 0, 0 ) ), 0.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( *outerRing1, QgsVertexId( 0, 0, 1 ) ), 1.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( *outerRing1, QgsVertexId( 0, 0, 2 ) ), 2.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( *outerRing1, QgsVertexId( 0, 0, 3 ) ), 3.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( *outerRing1, QgsVertexId( 0, 0, 4 ) ), 4.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( *outerRing1, QgsVertexId( 0, 0, 5 ) ), -1.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( *outerRing1, QgsVertexId( 0, 1, 1 ) ), -1.0 );
+
+  //test with polygon
+  QgsPolygonV2 polygon1;
+  polygon1.setExteriorRing( outerRing1 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( polygon1, QgsVertexId( 0, 0, 0 ) ), 0.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( polygon1, QgsVertexId( 0, 0, 1 ) ), 1.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( polygon1, QgsVertexId( 0, 0, 2 ) ), 2.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( polygon1, QgsVertexId( 0, 0, 3 ) ), 3.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( polygon1, QgsVertexId( 0, 0, 4 ) ), 4.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( polygon1, QgsVertexId( 0, 0, 5 ) ), -1.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( polygon1, QgsVertexId( 0, 1, 1 ) ), -1.0 );
+
+  //test with point
+  QgsPointV2 point( 1, 2 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( point, QgsVertexId( 0, 0, 0 ) ), 0.0 );
+  QCOMPARE( QgsGeometryUtils::distanceToVertex( point, QgsVertexId( 0, 0, 1 ) ), -1.0 );
+}
+
 
 QTEST_MAIN( TestQgsGeometryUtils )
 #include "testqgsgeometryutils.moc"

tests/src/python/test_qgsgeometry.py

@@ -1837,6 +1837,22 @@ def testAddMValue(self):
         wkt = geom.exportToWkt()
         assert compareWkt(expWkt, wkt), "addMValue to Point failed: mismatch Expected:\n%s\nGot:\n%s\n" % (expWkt, wkt)
 
+    def testDistanceToVertex(self):
+        """ Test distanceToVertex calculation """
+        g = QgsGeometry()
+        self.assertEqual(g.distanceToVertex(0), -1)
+
+        g = QgsGeometry.fromWkt('LineString ()')
+        self.assertEqual(g.distanceToVertex(0), -1)
+
+        g = QgsGeometry.fromWkt('Polygon ((0 0, 1 0, 1 1, 0 1, 0 0))')
+        self.assertEqual(g.distanceToVertex(0), 0)
+        self.assertEqual(g.distanceToVertex(1), 1)
+        self.assertEqual(g.distanceToVertex(2), 2)
+        self.assertEqual(g.distanceToVertex(3), 3)
+        self.assertEqual(g.distanceToVertex(4), 4)
+        self.assertEqual(g.distanceToVertex(5), -1)
+
     def testRelates(self):
         """ Test relationships between geometries. Note the bulk of these tests were taken from the PostGIS relate testdata """
         with open(os.path.join(TEST_DATA_DIR, 'relates_data.csv'), 'r') as d: