Allow using the longer arc with two point and center methods

qgis · Apr 23, 2018 · 9a6d966 · 9a6d966
1 parent 732d6bb
commit 9a6d966
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Showing 8 changed files with 41 additions and 9 deletions.
diff --git a/python/core/geometry/qgscircularstring.sip.in b/python/core/geometry/qgscircularstring.sip.in
@@ -41,11 +41,16 @@ arc passing through ``p1``, ``p2`` and ``p3``.
 
     static QgsCircularString fromTwoPointsAndCenter( const QgsPoint &p1,
         const QgsPoint &p2,
-        const QgsPoint &center );
+        const QgsPoint &center,
+        bool useShortestArc = true );
 %Docstring
 Creates a circular string with a single arc representing
 the curve from ``p1`` to ``p2`` with the specified ``center``.
 
+If ``useShortestArc`` is true, then the arc returned will be that corresponding
+to the shorter arc from ``p1`` to ``p2``. If it is false, the longer arc from ``p1``
+to ``p2`` will be used (i.e. winding the other way around the circle).
+
 .. versionadded:: 3.2
 %End
 

diff --git a/python/core/geometry/qgsgeometryutils.sip.in b/python/core/geometry/qgsgeometryutils.sip.in
@@ -277,11 +277,15 @@ first 3D point amongst ``p1`` and ``p2``.
 .. seealso:: :py:func:`segmentMidPointFromCenter`
 %End
 
-    static QgsPoint segmentMidPointFromCenter( const QgsPoint &p1, const QgsPoint &p2, const QgsPoint &center );
+    static QgsPoint segmentMidPointFromCenter( const QgsPoint &p1, const QgsPoint &p2, const QgsPoint &center, bool useShortestArc = true );
 %Docstring
 Calculates the midpoint on the circle passing through ``p1`` and ``p2``,
 with the specified ``center`` coordinate.
 
+If ``useShortestArc`` is true, then the midpoint returned will be that corresponding
+to the shorter arc from ``p1`` to ``p2``. If it is false, the longer arc from ``p1``
+to ``p2`` will be used (i.e. winding the other way around the circle).
+
 .. versionadded:: 3.2
 
 .. seealso:: :py:func:`segmentMidPoint`

diff --git a/src/core/geometry/qgscircularstring.cpp b/src/core/geometry/qgscircularstring.cpp
@@ -66,9 +66,9 @@ QgsCircularString::QgsCircularString( const QgsPoint &p1, const QgsPoint &p2, co
   }
 }
 
-QgsCircularString QgsCircularString::fromTwoPointsAndCenter( const QgsPoint &p1, const QgsPoint &p2, const QgsPoint &center )
+QgsCircularString QgsCircularString::fromTwoPointsAndCenter( const QgsPoint &p1, const QgsPoint &p2, const QgsPoint &center, const bool useShortestArc )
 {
-  const QgsPoint midPoint = QgsGeometryUtils::segmentMidPointFromCenter( p1, p2, center );
+  const QgsPoint midPoint = QgsGeometryUtils::segmentMidPointFromCenter( p1, p2, center, useShortestArc );
   return QgsCircularString( p1, midPoint, p2 );
 }
 

diff --git a/src/core/geometry/qgscircularstring.h b/src/core/geometry/qgscircularstring.h
@@ -54,11 +54,16 @@ class CORE_EXPORT QgsCircularString: public QgsCurve
      * Creates a circular string with a single arc representing
      * the curve from \a p1 to \a p2 with the specified \a center.
      *
+     * If \a useShortestArc is true, then the arc returned will be that corresponding
+     * to the shorter arc from \a p1 to \a p2. If it is false, the longer arc from \a p1
+     * to \a p2 will be used (i.e. winding the other way around the circle).
+     *
      * \since QGIS 3.2
      */
     static QgsCircularString fromTwoPointsAndCenter( const QgsPoint &p1,
         const QgsPoint &p2,
-        const QgsPoint &center );
+        const QgsPoint &center,
+        bool useShortestArc = true );
 
     bool equals( const QgsCurve &other ) const override;
 

diff --git a/src/core/geometry/qgsgeometryutils.cpp b/src/core/geometry/qgsgeometryutils.cpp
@@ -740,10 +740,12 @@ bool QgsGeometryUtils::segmentMidPoint( const QgsPoint &p1, const QgsPoint &p2,
   return true;
 }
 
-QgsPoint QgsGeometryUtils::segmentMidPointFromCenter( const QgsPoint &p1, const QgsPoint &p2, const QgsPoint &center )
+QgsPoint QgsGeometryUtils::segmentMidPointFromCenter( const QgsPoint &p1, const QgsPoint &p2, const QgsPoint &center, const bool useShortestArc )
 {
-  const double midPointAngle = averageAngle( lineAngle( center.x(), center.y(), p1.x(), p1.y() ),
-                               lineAngle( center.x(), center.y(), p2.x(), p2.y() ) );
+  double midPointAngle = averageAngle( lineAngle( center.x(), center.y(), p1.x(), p1.y() ),
+                                       lineAngle( center.x(), center.y(), p2.x(), p2.y() ) );
+  if ( !useShortestArc )
+    midPointAngle += M_PI;
   return center.project( center.distance( p1 ), midPointAngle * 180 / M_PI );
 }
 

diff --git a/src/core/geometry/qgsgeometryutils.h b/src/core/geometry/qgsgeometryutils.h
@@ -288,10 +288,14 @@ class CORE_EXPORT QgsGeometryUtils
      * Calculates the midpoint on the circle passing through \a p1 and \a p2,
      * with the specified \a center coordinate.
      *
+     * If \a useShortestArc is true, then the midpoint returned will be that corresponding
+     * to the shorter arc from \a p1 to \a p2. If it is false, the longer arc from \a p1
+     * to \a p2 will be used (i.e. winding the other way around the circle).
+     *
      * \since QGIS 3.2
      * \see segmentMidPoint()
      */
-    static QgsPoint segmentMidPointFromCenter( const QgsPoint &p1, const QgsPoint &p2, const QgsPoint &center );
+    static QgsPoint segmentMidPointFromCenter( const QgsPoint &p1, const QgsPoint &p2, const QgsPoint &center, bool useShortestArc = true );
 
     //! Calculates the direction angle of a circle tangent (clockwise from north in radians)
     static double circleTangentDirection( const QgsPoint &tangentPoint, const QgsPoint &cp1, const QgsPoint &cp2, const QgsPoint &cp3 );

diff --git a/tests/src/core/testqgsgeometry.cpp b/tests/src/core/testqgsgeometry.cpp
@@ -1221,6 +1221,15 @@ void TestQgsGeometry::circularString()
   QCOMPARE( from3Pts.yAt( 1 ), 22.0 );
   QCOMPARE( from3Pts.xAt( 2 ), 31.0 );
   QCOMPARE( from3Pts.yAt( 2 ), 2.0 );
+  from3Pts = QgsCircularString::fromTwoPointsAndCenter( QgsPoint( 1, 2 ), QgsPoint( 31, 2 ), QgsPoint( 21, 2 ), false );
+  QCOMPARE( from3Pts.wkbType(), QgsWkbTypes::CircularString );
+  QCOMPARE( from3Pts.numPoints(), 3 );
+  QCOMPARE( from3Pts.xAt( 0 ), 1.0 );
+  QCOMPARE( from3Pts.yAt( 0 ), 2.0 );
+  QCOMPARE( from3Pts.xAt( 1 ), 21.0 );
+  QCOMPARE( from3Pts.yAt( 1 ), -18.0 );
+  QCOMPARE( from3Pts.xAt( 2 ), 31.0 );
+  QCOMPARE( from3Pts.yAt( 2 ), 2.0 );
   from3Pts = QgsCircularString::fromTwoPointsAndCenter( QgsPoint( QgsWkbTypes::PointZ, 1, 2, 3 ), QgsPoint( QgsWkbTypes::PointZ, 32, 2, 33 ),
              QgsPoint( QgsWkbTypes::PointZ, 21, 2, 23 ) );
   QCOMPARE( from3Pts.wkbType(), QgsWkbTypes::CircularStringZ );

diff --git a/tests/src/core/testqgsgeometryutils.cpp b/tests/src/core/testqgsgeometryutils.cpp
@@ -220,6 +220,9 @@ void TestQgsGeometryUtils::testSegmentMidPointCenter()
   QgsPoint mid = QgsGeometryUtils::segmentMidPointFromCenter( QgsPoint( 10, 21 ), QgsPoint( 11, 20 ), QgsPoint( 10, 20 ) );
   QGSCOMPARENEAR( mid.x(), 10.7071, 0.0001 );
   QGSCOMPARENEAR( mid.y(), 20.7071, 0.0001 );
+  QgsGeometryUtils::segmentMidPointFromCenter( QgsPoint( 10, 21 ), QgsPoint( 11, 20 ), QgsPoint( 10, 20 ), false );
+  QGSCOMPARENEAR( mid.x(), 10.7071, 0.0001 );
+  QGSCOMPARENEAR( mid.y(), 20.7071, 0.0001 );
   mid = QgsGeometryUtils::segmentMidPointFromCenter( QgsPoint( 10, 21 ), QgsPoint( 9, 20 ), QgsPoint( 10, 20 ) );
   QGSCOMPARENEAR( mid.x(), 9.292893, 0.0001 );
   QGSCOMPARENEAR( mid.y(), 20.7071, 0.0001 );