Fix incorrect area calculation for polygon (fix #14675)

nyalldawson · nyalldawson · commit 5305486ec87f · 2016-07-01T18:39:00.000+10:00
(cherry-picked from bf4cf51)
diff --git a/src/core/qgsdistancearea.cpp b/src/core/qgsdistancearea.cpp
@@ -931,7 +931,8 @@ double QgsDistanceArea::computePolygonArea( const QList<QgsPoint>& points ) cons
     dx = x2 - x1;
     area += dx * ( m_Qp - getQ( y2 ) );
 
-    if (( dy = y2 - y1 ) != 0.0 )
+    dy = y2 - y1;
+    if ( !qgsDoubleNear( dy, 0.0 ) )
       area += dx * getQ( y2 ) - ( dx / dy ) * ( Qbar2 - Qbar1 );
   }
   if (( area *= m_AE ) < 0.0 )
diff --git a/tests/src/core/testqgsdistancearea.cpp b/tests/src/core/testqgsdistancearea.cpp
@@ -43,6 +43,7 @@ class TestQgsDistanceArea: public QObject
     void measureUnits();
     void measureAreaAndUnits();
     void emptyPolygon();
+    void regression14675();
 
 };
 
@@ -356,6 +357,17 @@ void TestQgsDistanceArea::emptyPolygon()
   da.measurePolygon( QList< QgsPoint >() );
 }
 
+void TestQgsDistanceArea::regression14675()
+{
+  //test regression #14675
+  QgsDistanceArea calc;
+  calc.setEllipsoidalMode( true );
+  calc.setEllipsoid( "GRS80" );
+  calc.setSourceCrs( 145L );
+  QgsGeometry geom( QgsGeometryFactory::geomFromWkt( "Polygon ((917593.5791854317067191 6833700.00807378999888897, 917596.43389983859378844 6833700.67099479306489229, 917599.53056440979707986 6833700.78673478215932846, 917593.5791854317067191 6833700.00807378999888897))" ) );
+  QVERIFY( qgsDoubleNear( calc.measureArea( &geom ), 0.83301, 0.0001 ) );
+}
+
 QTEST_MAIN( TestQgsDistanceArea )
 #include "testqgsdistancearea.moc"
 

Original file line number	Diff line number	Diff line change
`@@ -931,7 +931,8 @@ double QgsDistanceArea::computePolygonArea( const QList<QgsPoint>& points ) cons`
`931`	`931`	`dx = x2 - x1;`
`932`	`932`	`area += dx * ( m_Qp - getQ( y2 ) );`
`933`	`933`
`934`		`- if (( dy = y2 - y1 ) != 0.0 )`
	`934`	`+ dy = y2 - y1;`
	`935`	`+ if ( !qgsDoubleNear( dy, 0.0 ) )`
`935`	`936`	`area += dx * getQ( y2 ) - ( dx / dy ) * ( Qbar2 - Qbar1 );`
`936`	`937`	`}`
`937`	`938`	`if (( area *= m_AE ) < 0.0 )`