QgsLineStringV2 fixes

- fix incorrect centroid calculation (was always returning 0,0)
- fix closestSegment when numPoints < 2
- fix broken leftOf calculation for closestSegment
- area calculation when numPoints < 2

Plus add more unit tests

Author: nyalldawson

python/core/geometry/qgsabstractgeometryv2.sip

@@ -111,6 +111,16 @@ class QgsAbstractGeometryV2
     virtual void coordinateSequence( QList< QList< QList< QgsPointV2 > > >& coord /Out/ ) const = 0;
     int nCoordinates() const;
     virtual QgsPointV2 vertexAt( const QgsVertexId& id ) const = 0;
+
+    /** Searches for the closest segment of the geometry to a given point.
+     * @param pt specifies the point to find closest segment to
+     * @param segmentPt storage for the closest point within the geometry
+     * @param vertexAfter storage for the ID of the vertex at the end of the closest segment
+     * @param leftOf returns whether the point lies on the left side of the nearest segment (true if point is to left of segment,
+     * false if point is to right of segment)
+     * @param epsilon epsilon for segment snapping
+     * @returns squared distance to closest segment
+     */
     virtual double closestSegment( const QgsPointV2& pt, QgsPointV2& segmentPt,  QgsVertexId& vertexAfter, bool* leftOf, double epsilon ) const = 0;
 
     //low-level editing

python/core/geometry/qgslinestringv2.sip

@@ -152,6 +152,8 @@ class QgsLineStringV2: public QgsCurveV2
     double closestSegment( const QgsPointV2& pt, QgsPointV2& segmentPt,  QgsVertexId& vertexAfter, bool* leftOf, double epsilon ) const;
     bool pointAt( int i, QgsPointV2& vertex, QgsVertexId::VertexType& type ) const;
 
+    virtual QgsPointV2 centroid() const;
+
     void sumUpArea( double& sum ) const;
     double vertexAngle( const QgsVertexId& vertex ) const;
 

src/core/geometry/qgsabstractgeometryv2.h

@@ -222,10 +222,11 @@ class CORE_EXPORT QgsAbstractGeometryV2
     virtual QgsPointV2 vertexAt( const QgsVertexId& id ) const = 0;
 
     /** Searches for the closest segment of the geometry to a given point.
-     * @param pt Specifies the point for search
+     * @param pt specifies the point to find closest segment to
      * @param segmentPt storage for the closest point within the geometry
-     * @param vertexAfter storage for the id of the vertex after the closest segment
-     * @param leftOf returns if the point lies on the left of right side of the segment ( < 0 means left, > 0 means right )
+     * @param vertexAfter storage for the ID of the vertex at the end of the closest segment
+     * @param leftOf returns whether the point lies on the left side of the nearest segment (true if point is to left of segment,
+     * false if point is to right of segment)
      * @param epsilon epsilon for segment snapping
      * @returns squared distance to closest segment
      */

src/core/geometry/qgscircularstringv2.cpp

@@ -810,14 +810,14 @@ double QgsCircularStringV2::closestSegment( const QgsPointV2& pt, QgsPointV2& se
   return minDist;
 }
 
-bool QgsCircularStringV2::pointAt( int i, QgsPointV2& vertex, QgsVertexId::VertexType& type ) const
+bool QgsCircularStringV2::pointAt( int node, QgsPointV2& point, QgsVertexId::VertexType& type ) const
 {
-  if ( i >= numPoints() )
+  if ( node >= numPoints() )
   {
     return false;
   }
-  vertex = pointN( i );
-  type = ( i % 2 == 0 ) ? QgsVertexId::SegmentVertex : QgsVertexId::CurveVertex;
+  point = pointN( node );
+  type = ( node % 2 == 0 ) ? QgsVertexId::SegmentVertex : QgsVertexId::CurveVertex;
   return true;
 }
 

src/core/geometry/qgscircularstringv2.h

@@ -108,7 +108,7 @@ class CORE_EXPORT QgsCircularStringV2: public QgsCurveV2
     /**
      * @copydoc QgsCurveV2::pointAt()
      */
-    bool pointAt( int i, QgsPointV2& vertex, QgsVertexId::VertexType& type ) const override;
+    bool pointAt( int node, QgsPointV2& point, QgsVertexId::VertexType& type ) const override;
 
     /**
      * @copydoc QgsCurveV2::sumUpArea()

src/core/geometry/qgscompoundcurvev2.cpp

@@ -557,15 +557,15 @@ double QgsCompoundCurveV2::closestSegment( const QgsPointV2& pt, QgsPointV2& seg
   return QgsGeometryUtils::closestSegmentFromComponents( mCurves, QgsGeometryUtils::VERTEX, pt, segmentPt, vertexAfter, leftOf, epsilon );
 }
 
-bool QgsCompoundCurveV2::pointAt( int i, QgsPointV2& vertex, QgsVertexId::VertexType& type ) const
+bool QgsCompoundCurveV2::pointAt( int node, QgsPointV2& point, QgsVertexId::VertexType& type ) const
 {
   int currentVertexId = 0;
   for ( int j = 0; j < mCurves.size(); ++j )
   {
     int nCurvePoints = mCurves.at( j )->numPoints();
-    if (( i - currentVertexId ) < nCurvePoints )
+    if (( node - currentVertexId ) < nCurvePoints )
     {
-      return ( mCurves.at( j )->pointAt( i - currentVertexId, vertex, type ) );
+      return ( mCurves.at( j )->pointAt( node - currentVertexId, point, type ) );
     }
     currentVertexId += ( nCurvePoints - 1 );
   }

src/core/geometry/qgscompoundcurvev2.h

@@ -95,7 +95,7 @@ class CORE_EXPORT QgsCompoundCurveV2: public QgsCurveV2
     virtual bool deleteVertex( const QgsVertexId& position ) override;
 
     virtual double closestSegment( const QgsPointV2& pt, QgsPointV2& segmentPt,  QgsVertexId& vertexAfter, bool* leftOf, double epsilon ) const override;
-    bool pointAt( int i, QgsPointV2& vertex, QgsVertexId::VertexType& type ) const override;
+    bool pointAt( int node, QgsPointV2& point, QgsVertexId::VertexType& type ) const override;
 
     void sumUpArea( double& sum ) const override;
 

src/core/geometry/qgscurvev2.h

@@ -84,8 +84,12 @@ class CORE_EXPORT QgsCurveV2: public QgsAbstractGeometryV2
     virtual bool nextVertex( QgsVertexId& id, QgsPointV2& vertex ) const override;
 
     /** Returns the point and vertex id of a point within the curve.
+     * @param node node number, where the first node is 0
+     * @param point will be set to point at corresponding node in the curve
+     * @param type will be set to the vertex type of the node
+     * @returns true if node exists within the curve
      */
-    virtual bool pointAt( int i, QgsPointV2& vertex, QgsVertexId::VertexType& type ) const = 0;
+    virtual bool pointAt( int node, QgsPointV2& point, QgsVertexId::VertexType& type ) const = 0;
 
     /** Returns a reversed copy of the curve, where the direction of the curve has been flipped.
      * @note added in QGIS 2.14

src/core/geometry/qgslinestringv2.cpp

@@ -24,6 +24,7 @@
 #include <QPainter>
 #include <limits>
 #include <QDomDocument>
+#include <QtCore/qmath.h>
 
 QgsLineStringV2::QgsLineStringV2(): QgsCurveV2()
 {
@@ -573,6 +574,17 @@ double QgsLineStringV2::closestSegment( const QgsPointV2& pt, QgsPointV2& segmen
   double segmentPtX, segmentPtY;
 
   int size = mX.size();
+  if ( size == 0 )
+  {
+    vertexAfter = QgsVertexId( 0, 0, 0 );
+    return sqrDist;
+  }
+  else if ( size == 1 )
+  {
+    segmentPt = pointN( 0 );
+    vertexAfter = QgsVertexId( 0, 0, 1 );
+    return QgsGeometryUtils::sqrDistance2D( pt, segmentPt );
+  }
   for ( int i = 1; i < size; ++i )
   {
     double prevX = mX.at( i - 1 );
@@ -587,28 +599,69 @@ double QgsLineStringV2::closestSegment( const QgsPointV2& pt, QgsPointV2& segmen
       segmentPt.setY( segmentPtY );
       if ( leftOf )
       {
-        *leftOf = ( QgsGeometryUtils::leftOfLine( segmentPtX, segmentPtY, prevX, prevY, pt.x(), pt.y() ) < 0 );
+        *leftOf = ( QgsGeometryUtils::leftOfLine( pt.x(), pt.y(), prevX, prevY, currentX, currentY ) < 0 );
       }
       vertexAfter.part = 0; vertexAfter.ring = 0; vertexAfter.vertex = i;
     }
   }
   return sqrDist;
 }
 
-bool QgsLineStringV2::pointAt( int i, QgsPointV2& vertex, QgsVertexId::VertexType& type ) const
+bool QgsLineStringV2::pointAt( int node, QgsPointV2& point, QgsVertexId::VertexType& type ) const
 {
-  if ( i >= numPoints() )
+  if ( node < 0 || node >= numPoints() )
   {
     return false;
   }
-  vertex = pointN( i );
+  point = pointN( node );
   type = QgsVertexId::SegmentVertex;
   return true;
 }
 
+QgsPointV2 QgsLineStringV2::centroid() const
+{
+  if ( mX.isEmpty() )
+    return QgsPointV2();
+
+  int numPoints = mX.count();
+  if ( numPoints == 1 )
+    return QgsPointV2( mX.at( 0 ), mY.at( 0 ) );
+
+  double totalLineLength = 0.0;
+  double prevX = mX.at( 0 );
+  double prevY = mY.at( 0 );
+  double sumX = 0.0;
+  double sumY = 0.0;
+
+  for ( int i = 1; i < numPoints ; ++i )
+  {
+    double currentX = mX.at( i );
+    double currentY = mY.at( i );
+    double segmentLength = sqrt( qPow( currentX - prevX, 2.0 ) +
+                                 qPow( currentY - prevY, 2.0 ) );
+    if ( qgsDoubleNear( segmentLength, 0.0 ) )
+      continue;
+
+    totalLineLength += segmentLength;
+    sumX += segmentLength * 0.5 * ( currentX + prevX );
+    sumY += segmentLength * 0.5 * ( currentY + prevY );
+    prevX = currentX;
+    prevY = currentY;
+  }
+
+  if ( qgsDoubleNear( totalLineLength, 0.0 ) )
+    return QgsPointV2( mX.at( 0 ), mY.at( 0 ) );
+  else
+    return QgsPointV2( sumX / totalLineLength, sumY / totalLineLength );
+
+}
+
 void QgsLineStringV2::sumUpArea( double& sum ) const
 {
   int maxIndex = numPoints() - 1;
+  if ( maxIndex == 1 )
+    return; //no area, just a single line
+
   for ( int i = 0; i < maxIndex; ++i )
   {
     sum += 0.5 * ( mX.at( i ) * mY.at( i + 1 ) - mY.at( i ) * mX.at( i + 1 ) );

src/core/geometry/qgslinestringv2.h

@@ -171,7 +171,9 @@ class CORE_EXPORT QgsLineStringV2: public QgsCurveV2
     virtual QgsLineStringV2* reversed() const override;
 
     double closestSegment( const QgsPointV2& pt, QgsPointV2& segmentPt,  QgsVertexId& vertexAfter, bool* leftOf, double epsilon ) const override;
-    bool pointAt( int i, QgsPointV2& vertex, QgsVertexId::VertexType& type ) const override;
+    bool pointAt( int node, QgsPointV2& point, QgsVertexId::VertexType& type ) const override;
+
+    virtual QgsPointV2 centroid() const override;
 
     void sumUpArea( double& sum ) const override;
     double vertexAngle( const QgsVertexId& vertex ) const override;