QgsGeometryUtils fixes

- add QgsGeometryUtils::normalizedAngle for restricting an angle
to [0, 2PI)
- fix calculations of QgsGeometryUtils::averageAngle, was returning
perpendicular angle and angles > 2Pi
- improve docs and add unit tests

Author: nyalldawson

src/core/geometry/qgsgeometryutils.cpp

@@ -613,6 +613,20 @@ QString QgsGeometryUtils::pointsToJSON( const QList<QgsPointV2>& points, int pre
   return json;
 }
 
+double QgsGeometryUtils::normalizedAngle( double angle )
+{
+  double clippedAngle = angle;
+  if ( clippedAngle >= M_PI * 2 || clippedAngle <= -2 * M_PI )
+  {
+    clippedAngle = fmod( clippedAngle, 2 * M_PI );
+  }
+  if ( clippedAngle < 0.0 )
+  {
+    clippedAngle += 2 * M_PI;
+  }
+  return clippedAngle;
+}
+
 QPair<QgsWKBTypes::Type, QString> QgsGeometryUtils::wktReadBlock( const QString &wkt )
 {
   QgsWKBTypes::Type wkbType = QgsWKBTypes::parseType( wkt );
@@ -662,38 +676,28 @@ double QgsGeometryUtils::lineAngle( double x1, double y1, double x2, double y2 )
 {
   double at = atan2( y2 - y1, x2 - x1 );
   double a = -at + M_PI / 2.0;
-  if ( a < 0 )
-  {
-    a = 2 * M_PI + a;
-  }
-  if ( a >= 2 * M_PI )
-  {
-    a -= 2 * M_PI;
-  }
-  return a;
+  return normalizedAngle( a );
 }
 
 double QgsGeometryUtils::linePerpendicularAngle( double x1, double y1, double x2, double y2 )
 {
   double a = lineAngle( x1, y1, x2, y2 );
   a += ( M_PI / 2.0 );
-  if ( a >= 2 * M_PI )
-  {
-    a -= ( 2 * M_PI );
-  }
-  return a;
+  return normalizedAngle( a );
 }
 
 double QgsGeometryUtils::averageAngle( double x1, double y1, double x2, double y2, double x3, double y3 )
 {
   // calc average angle between the previous and next point
-  double a1 = linePerpendicularAngle( x1, y1, x2, y2 );
-  double a2 = linePerpendicularAngle( x2, y2, x3, y3 );
+  double a1 = lineAngle( x1, y1, x2, y2 );
+  double a2 = lineAngle( x2, y2, x3, y3 );
   return averageAngle( a1, a2 );
 }
 
 double QgsGeometryUtils::averageAngle( double a1, double a2 )
 {
+  a1 = normalizedAngle( a1 );
+  a2 = normalizedAngle( a2 );
   double clockwiseDiff = 0.0;
   if ( a2 >= a1 )
   {
@@ -714,14 +718,5 @@ double QgsGeometryUtils::averageAngle( double a1, double a2 )
   {
     resultAngle = a1 - counterClockwiseDiff / 2.0;
   }
-
-  if ( resultAngle >= 2 * M_PI )
-  {
-    resultAngle -= 2 * M_PI;
-  }
-  else if ( resultAngle < 0 )
-  {
-    resultAngle = 2 * M_PI - resultAngle;
-  }
-  return resultAngle;
+  return normalizedAngle( resultAngle );
 }

src/core/geometry/qgsgeometryutils.h

@@ -151,15 +151,41 @@ class CORE_EXPORT QgsGeometryUtils
     static QDomElement pointsToGML3( const QList<QgsPointV2>& points, QDomDocument &doc, int precision, const QString& ns, bool is3D );
     /** Returns a geoJSON coordinates string */
     static QString pointsToJSON( const QList<QgsPointV2>& points, int precision );
-    /** Calculates direction of line (clockwise from north direction) in radians*/
+
+    /** Ensures that an angle is in the range 0 <= angle < 2 pi.
+     * @param angle angle in radians
+     * @returns equivalent angle within the range [0, 2 pi)
+    */
+    static double normalizedAngle( double angle );
+
+    /** Calculates the direction of line joining two points in radians, clockwise from the north direction.
+     * @param x1 x-coordinate of line start
+     * @param y1 y-coordinate of line start
+     * @param x2 x-coordinate of line end
+     * @param y2 y-coordinate of line end
+     * @returns angle in radians. Returned value is undefined if start and end point are the same.
+    */
     static double lineAngle( double x1, double y1, double x2, double y2 );
-    /** Calculates angle perpendicular to line*/
+
+    /** Calculates the perpendicular angle to a line joining two points. Returned angle is in radians,
+     * clockwise from the north direction.
+     * @param x1 x-coordinate of line start
+     * @param y1 y-coordinate of line start
+     * @param x2 x-coordinate of line end
+     * @param y2 y-coordinate of line end
+     * @returns angle in radians. Returned value is undefined if start and end point are the same.
+    */
     static double linePerpendicularAngle( double x1, double y1, double x2, double y2 );
+
     /** Angle between two linear segments*/
     static double averageAngle( double x1, double y1, double x2, double y2, double x3, double y3 );
-    /** Averages two angles*/
-    static double averageAngle( double a1, double a2 );
 
+    /** Averages two angles, correctly handling negative angles and ensuring the result is between 0 and 2 pi.
+     * @param a1 first angle (in radians)
+     * @param a2 second angle (in radians)
+     * @returns average angle (in radians)
+    */
+    static double averageAngle( double a1, double a2 );
 
     /** Parses a WKT block of the format "TYPE( contents )" and returns a pair of geometry type to contents ("Pair(wkbType, "contents")")
      */

tests/src/core/testqgsgeometry.cpp

@@ -28,6 +28,7 @@
 //qgis includes...
 #include <qgsapplication.h>
 #include <qgsgeometry.h>
+#include "qgsgeometryutils.h"
 #include <qgspoint.h>
 #include "qgspointv2.h"
 #include "qgslinestringv2.h"
@@ -56,6 +57,7 @@ class TestQgsGeometry : public QObject
     void isEmpty();
     void pointV2(); //test QgsPointV2
     void lineStringV2(); //test QgsLineStringV2
+    void utils(); //test QgsGeometryUtils
 
     void fromQgsPoint();
     void fromQPoint();
@@ -1842,6 +1844,49 @@ void TestQgsGeometry::lineStringV2()
 
 }
 
+void TestQgsGeometry::utils()
+{
+  //test normalizedAngle
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( 0.0 ), 0.0, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( 1.5708 ), 1.5708, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( 3.1416 ), 3.1416, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( 4.7124 ), 4.7124, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( 2 * M_PI ), 0.0, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( 6.80678 ), 0.5236, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( 12.5664 ), 0.0, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( 12.7409 ), 0.174533, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( -0.174533 ), 6.10865, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( -6.28318 ), 0.0, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( -6.45772 ), 6.10865, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::normalizedAngle( -13.2645 ), 5.58505, 0.0001 ) );
+
+  //test lineAngle
+  ( void )QgsGeometryUtils::lineAngle( 0.0, 0.0, 0.0, 0.0 ); //undefined, but don't want a crash
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::lineAngle( 0.0, 0.0, 0.0, 1.0 ), 0.0, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::lineAngle( 0.0, 0.0, 1.0, 1.0 ), 0.7854, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::lineAngle( 0.0, 0.0, 1.0, 0.0 ), 1.5708, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::lineAngle( 0.0, 0.0, 0.0, -1.0 ), 3.1416, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::lineAngle( 0.0, 0.0, -1.0, 0.0 ), 4.7124, 0.0001 ) );
+
+  //test linePerpendicularAngle
+  ( void )QgsGeometryUtils::linePerpendicularAngle( 0.0, 0.0, 0.0, 0.0 ); //undefined, but don't want a crash
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::linePerpendicularAngle( 0.0, 0.0, 0.0, 1.0 ), 1.5708, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::linePerpendicularAngle( 0.0, 0.0, 1.0, 1.0 ), 2.3562, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::linePerpendicularAngle( 0.0, 0.0, 1.0, 0.0 ), 3.1416, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::linePerpendicularAngle( 0.0, 0.0, 0.0, -1.0 ), 4.7124, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::linePerpendicularAngle( 0.0, 0.0, -1.0, 0.0 ), 0.0, 0.0001 ) );
+
+  //test averageAngle
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::averageAngle( 0.0, 0.0 ), 0.0, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::averageAngle( 0.0, 6.28319 ), 0.0, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::averageAngle( 0.0, 12.5664 ), 0.0, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::averageAngle( 6.28319, 0.0 ), 0.0, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::averageAngle( -6.28318, 0.0 ), 0.0, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::averageAngle( -6.28318, -6.28318 ), 0.0, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::averageAngle( 0.0, 3.141592 ), 1.5708, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::averageAngle( 0.0, -3.141592 ), 4.71239, 0.0001 ) );
+  QVERIFY( qgsDoubleNear( QgsGeometryUtils::averageAngle( 5.49779, 4.71239 ), 5.1051, 0.0001 ) );
+}
 
 void TestQgsGeometry::fromQgsPoint()
 {