Add QgsGeometryUtils method for interpolating point between two point…

…s, with z/m handling
qgis · Aug 15, 2018 · 56fd4e3 · 56fd4e3
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Showing 4 changed files with 126 additions and 9 deletions.
diff --git a/python/core/auto_generated/geometry/qgsgeometryutils.sip.in b/python/core/auto_generated/geometry/qgsgeometryutils.sip.in
@@ -228,9 +228,10 @@ on the line, or exactly in line with the segment) and the result is undefined.
 
     static QgsPoint pointOnLineWithDistance( const QgsPoint &startPoint, const QgsPoint &directionPoint, double distance );
 %Docstring
-Returns a point a specified distance toward a second point.
+Returns a point a specified ``distance`` toward a second point.
 %End
 
+
     static double ccwAngle( double dy, double dx );
 %Docstring
 Returns the counter clockwise angle between a line with components dx, dy and the line with dx > 0 and dy = 0

diff --git a/src/core/geometry/qgsgeometryutils.cpp b/src/core/geometry/qgsgeometryutils.cpp
@@ -542,17 +542,36 @@ int QgsGeometryUtils::leftOfLine( double x, double y, double x1, double y1, doub
 
 QgsPoint QgsGeometryUtils::pointOnLineWithDistance( const QgsPoint &startPoint, const QgsPoint &directionPoint, double distance )
 {
-  double dx = directionPoint.x() - startPoint.x();
-  double dy = directionPoint.y() - startPoint.y();
-  double length = std::sqrt( dx * dx + dy * dy );
+  double x, y;
+  pointOnLineWithDistance( startPoint.x(), startPoint.y(), directionPoint.x(), directionPoint.y(), distance, x, y );
+  return QgsPoint( x, y );
+}
+
+void QgsGeometryUtils::pointOnLineWithDistance( double x1, double y1, double x2, double y2, double distance, double &x, double &y, double *z1, double *z2, double *z, double *m1, double *m2, double *m )
+{
+  const double dx = x2 - x1;
+  const double dy = y2 - y1;
+  const double length = std::sqrt( dx * dx + dy * dy );
 
   if ( qgsDoubleNear( length, 0.0 ) )
   {
-    return startPoint;
+    x = x1;
+    y = y1;
+    if ( z && z1 )
+      *z = *z1;
+    if ( m && m1 )
+      *m = *m1;
+  }
+  else
+  {
+    const double scaleFactor = distance / length;
+    x = x1 + dx * scaleFactor;
+    y = y1 + dy * scaleFactor;
+    if ( z && z1 && z2 )
+      *z = *z1 + ( *z2 - *z1 ) * scaleFactor;
+    if ( m && m1 && m2 )
+      *m = *m1 + ( *m2 - *m1 ) * scaleFactor;
   }
-
-  double scaleFactor = distance / length;
-  return QgsPoint( startPoint.x() + dx * scaleFactor, startPoint.y() + dy * scaleFactor );
 }
 
 double QgsGeometryUtils::ccwAngle( double dy, double dx )

diff --git a/src/core/geometry/qgsgeometryutils.h b/src/core/geometry/qgsgeometryutils.h
@@ -247,10 +247,23 @@ class CORE_EXPORT QgsGeometryUtils
     static int leftOfLine( double x, double y, double x1, double y1, double x2, double y2 );
 
     /**
-     * Returns a point a specified distance toward a second point.
+     * Returns a point a specified \a distance toward a second point.
      */
     static QgsPoint pointOnLineWithDistance( const QgsPoint &startPoint, const QgsPoint &directionPoint, double distance );
 
+    /**
+     * Calculates the point a specified \a distance from (\a x1, \a y1) toward a second point (\a x2, \a y2).
+     *
+     * Optionally, interpolated z and m values can be obtained by specifying the \a z1, \a z2 and \a z arguments
+     * and/or the \a m1, \a m2, \a m arguments.
+     *
+     * \note Not available in Python bindings
+     * \since QGIS 3.4
+     */
+    static void pointOnLineWithDistance( double x1, double y1, double x2, double y2, double distance, double &x, double &y,
+                                         double *z1 = nullptr, double *z2 = nullptr, double *z = nullptr,
+                                         double *m1 = nullptr, double *m2 = nullptr, double *m = nullptr ) SIP_SKIP;
+
     //! Returns the counter clockwise angle between a line with components dx, dy and the line with dx > 0 and dy = 0
     static double ccwAngle( double dy, double dx );
 

diff --git a/tests/src/core/testqgsgeometryutils.cpp b/tests/src/core/testqgsgeometryutils.cpp
@@ -68,6 +68,7 @@ class TestQgsGeometryUtils: public QObject
     void testInterpolatePointOnLineQgsPoint();
     void testInterpolatePointOnLine();
     void testInterpolatePointOnLineByValue();
+    void testPointOnLineWithDistance();
 };
 
 
@@ -1095,5 +1096,88 @@ void TestQgsGeometryUtils::testInterpolatePointOnLineByValue()
   QCOMPARE( p.y(), 0.0 );
 }
 
+void TestQgsGeometryUtils::testPointOnLineWithDistance()
+{
+  QgsPoint p = QgsGeometryUtils::pointOnLineWithDistance( QgsPoint( 0, 0 ), QgsPoint( 10, 0 ), 0 );
+  QCOMPARE( p.x(), 0.0 );
+  QCOMPARE( p.y(), 0.0 );
+  double x;
+  double y;
+  QgsGeometryUtils::pointOnLineWithDistance( 0, 0, 10, 0, 0, x, y );
+  QCOMPARE( x, 0.0 );
+  QCOMPARE( y, 0.0 );
+
+  p = QgsGeometryUtils::pointOnLineWithDistance( QgsPoint( 2, 3 ),  QgsPoint( 12, 3 ), 10 );
+  QCOMPARE( p.x(), 12.0 );
+  QCOMPARE( p.y(), 3.0 );
+  QgsGeometryUtils::pointOnLineWithDistance( 2, 3,  12, 3, 10, x, y );
+  QCOMPARE( x, 12.0 );
+  QCOMPARE( y, 3.0 );
+
+  p = QgsGeometryUtils::pointOnLineWithDistance( QgsPoint( 0, 0 ),  QgsPoint( 0, 10 ), 0 );
+  QCOMPARE( p.x(), 0.0 );
+  QCOMPARE( p.y(), 0.0 );
+  QgsGeometryUtils::pointOnLineWithDistance( 0, 0,  0, 10, 0, x, y );
+  QCOMPARE( x, 0.0 );
+  QCOMPARE( y, 0.0 );
+
+  p = QgsGeometryUtils::pointOnLineWithDistance( QgsPoint( 0, 0 ),  QgsPoint( 0, 10 ), 10 );
+  QCOMPARE( p.x(), 0.0 );
+  QCOMPARE( p.y(), 10.0 );
+  QgsGeometryUtils::pointOnLineWithDistance( 0, 0,  0, 10, 10, x, y );
+  QCOMPARE( x, 0.0 );
+  QCOMPARE( y, 10.0 );
+
+  p = QgsGeometryUtils::pointOnLineWithDistance( QgsPoint( 2, 1 ),  QgsPoint( -8, -5 ), 5 );
+  QGSCOMPARENEAR( p.x(), -2.28746, 0.0001 );
+  QGSCOMPARENEAR( p.y(), -1.57248, 0.0001 );
+  QgsGeometryUtils::pointOnLineWithDistance( 2, 1, -8, -5, 5, x, y );
+  QGSCOMPARENEAR( x, -2.28746, 0.0001 );
+  QGSCOMPARENEAR( y, -1.57248, 0.0001 );
+  double z, z1, z2;
+  double m, m1, m2;
+  z1 = 12;
+  z2 = 2;
+  m1 = 11;
+  m2 = 15;
+  QgsGeometryUtils::pointOnLineWithDistance( 2, 1, -8, -5, 5, x, y, &z1, &z2, &z );
+  QGSCOMPARENEAR( x, -2.28746, 0.0001 );
+  QGSCOMPARENEAR( y, -1.57248, 0.0001 );
+  QGSCOMPARENEAR( z, 7.712535, 0.0001 );
+  QgsGeometryUtils::pointOnLineWithDistance( 2, 1, -8, -5, 5, x, y, nullptr, nullptr, nullptr, &m1, &m2, &m );
+  QGSCOMPARENEAR( x, -2.28746, 0.0001 );
+  QGSCOMPARENEAR( y, -1.57248, 0.0001 );
+  QGSCOMPARENEAR( m, 12.714986, 0.0001 );
+  z = 0;
+  m = 0;
+  QgsGeometryUtils::pointOnLineWithDistance( 2, 1, -8, -5, 5, x, y, &z1, &z2, &z, &m1, &m2, &m );
+  QGSCOMPARENEAR( x, -2.28746, 0.0001 );
+  QGSCOMPARENEAR( y, -1.57248, 0.0001 );
+  QGSCOMPARENEAR( z, 7.712535, 0.0001 );
+  QGSCOMPARENEAR( m, 12.714986, 0.0001 );
+
+  p = QgsGeometryUtils::pointOnLineWithDistance( QgsPoint( 0, 0 ),  QgsPoint( -10, -6 ), 2 );
+  QGSCOMPARENEAR( p.x(), -1.71499, 0.0001 );
+  QGSCOMPARENEAR( p.y(), -1.02899, 0.0001 );
+  QgsGeometryUtils::pointOnLineWithDistance( 0, 0, -10, -6, 2, x, y );
+  QGSCOMPARENEAR( x, -1.71499, 0.0001 );
+  QGSCOMPARENEAR( y, -1.02899, 0.0001 );
+
+  p = QgsGeometryUtils::pointOnLineWithDistance( QgsPoint( 0, 0 ),  QgsPoint( -10, -6 ), 20 );
+  QGSCOMPARENEAR( p.x(), -17.1499, 0.0001 );
+  QGSCOMPARENEAR( p.y(), -10.2899, 0.0001 );
+  QgsGeometryUtils::pointOnLineWithDistance( 0, 0, -10, -6, 20, x, y );
+  QGSCOMPARENEAR( x, -17.1499, 0.0001 );
+  QGSCOMPARENEAR( y, -10.2899, 0.0001 );
+
+  p = QgsGeometryUtils::pointOnLineWithDistance( QgsPoint( 0, 0 ),  QgsPoint( -10, -6 ), -10 );
+  QGSCOMPARENEAR( p.x(), 8.57493, 0.0001 );
+  QGSCOMPARENEAR( p.y(), 5.14496, 0.0001 );
+  QgsGeometryUtils::pointOnLineWithDistance( 0, 0, -10, -6, -10, x, y );
+  QGSCOMPARENEAR( x, 8.57493, 0.0001 );
+  QGSCOMPARENEAR( y, 5.14496, 0.0001 );
+
+}
+
 QGSTEST_MAIN( TestQgsGeometryUtils )
 #include "testqgsgeometryutils.moc"