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Port grass followup to area calculation fix

Browse Source 
https://trac.osgeo.org/grass/changeset/71259

refs discussion at

https://trac.osgeo.org/grass/ticket/3369
This commit is contained in:
Nyall Dawson 2017-07-13 07:41:42 +10:00
parent 7cbf9df21a
commit 773b2e7f9e
2 changed files with 9 additions and 8 deletions
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13
src/core/qgsdistancearea.cpp
View File

@ -674,17 +674,18 @@ double QgsDistanceArea::computePolygonArea( const QList<QgsPointXY> &points ) co
return 0; return 0;
} }
// IMPORTANT
// don't change anything here without reporting the changes to upstream (GRASS)
// let's all be good opensource citizens and share the improvements!
double x1, y1, x2, y2, dx, dy; double x1, y1, x2, y2, dx, dy;
double Qbar1, Qbar2; double Qbar1, Qbar2;
double area; double area;
/* GRASS comment: threshold for dy, should be between 1e-4 and 1e-7 /* GRASS comment: threshold for dy, should be between 1e-4 and 1e-7
* QGIS note: while the grass comment states that thres should be between 1e-4->1e-7, * See relevant discussion at https://trac.osgeo.org/grass/ticket/3369
* a value of 1e-7 caused TestQgsDistanceArea::regression14675() to regress
* The maximum threshold possible which permits regression14675() to pass
* was found to be ~0.7e-7.
*/ */
const double thresh = 0.7e-7; const double thresh = 1e-6;
QgsDebugMsgLevel( "Ellipsoid: " + mEllipsoid, 3 ); QgsDebugMsgLevel( "Ellipsoid: " + mEllipsoid, 3 );
if ( !willUseEllipsoid() ) if ( !willUseEllipsoid() )
@ -732,7 +733,7 @@ double QgsDistanceArea::computePolygonArea( const QList<QgsPointXY> &points ) co
* (Qbar2 - Qbar1) / dy should approach Q((y1 + y2) / 2) * (Qbar2 - Qbar1) / dy should approach Q((y1 + y2) / 2)
* Metz 2017 * Metz 2017
*/ */
area += dx * ( m_Qp - getQ( y2 ) ); area += dx * ( m_Qp - getQ( ( y1 + y2 ) / 2.0 ) );
/* original: /* original:
* area += dx * getQ( y2 ) - ( dx / dy ) * ( Qbar2 - Qbar1 ); * area += dx * getQ( y2 ) - ( dx / dy ) * ( Qbar2 - Qbar1 );

4
tests/src/core/testqgsdistancearea.cpp
View File

@ -377,7 +377,7 @@ void TestQgsDistanceArea::regression14675()
calc.setSourceCrs( QgsCoordinateReferenceSystem::fromSrsId( 145L ) ); calc.setSourceCrs( QgsCoordinateReferenceSystem::fromSrsId( 145L ) );
QgsGeometry geom( QgsGeometryFactory::geomFromWkt( QStringLiteral( "Polygon ((917593.5791854317067191 6833700.00807378999888897, 917596.43389983859378844 6833700.67099479306489229, 917599.53056440979707986 6833700.78673478215932846, 917593.5791854317067191 6833700.00807378999888897))" ) ) ); QgsGeometry geom( QgsGeometryFactory::geomFromWkt( QStringLiteral( "Polygon ((917593.5791854317067191 6833700.00807378999888897, 917596.43389983859378844 6833700.67099479306489229, 917599.53056440979707986 6833700.78673478215932846, 917593.5791854317067191 6833700.00807378999888897))" ) ) );
//lots of tolerance here - the formulas get quite unstable with small areas due to division by very small floats //lots of tolerance here - the formulas get quite unstable with small areas due to division by very small floats
QGSCOMPARENEAR( calc.measureArea( geom ), 0.83301, 0.02 ); QGSCOMPARENEAR( calc.measureArea( geom ), 0.833010, 0.03 );
} }
void TestQgsDistanceArea::regression16820() void TestQgsDistanceArea::regression16820()
@ -387,7 +387,7 @@ void TestQgsDistanceArea::regression16820()
calc.setSourceCrs( QgsCoordinateReferenceSystem( QStringLiteral( "EPSG:32634" ) ) ); calc.setSourceCrs( QgsCoordinateReferenceSystem( QStringLiteral( "EPSG:32634" ) ) );
QgsGeometry geom( QgsGeometryFactory::geomFromWkt( QStringLiteral( "Polygon ((110250.54038314701756462 5084495.57398066483438015, 110243.46975068224128336 5084507.17200060561299324, 110251.23908144699817058 5084506.68309532757848501, 110251.2394439501222223 5084506.68307251576334238, 110250.54048078990308568 5084495.57553235255181789, 110250.54038314701756462 5084495.57398066483438015))" ) ) ); QgsGeometry geom( QgsGeometryFactory::geomFromWkt( QStringLiteral( "Polygon ((110250.54038314701756462 5084495.57398066483438015, 110243.46975068224128336 5084507.17200060561299324, 110251.23908144699817058 5084506.68309532757848501, 110251.2394439501222223 5084506.68307251576334238, 110250.54048078990308568 5084495.57553235255181789, 110250.54038314701756462 5084495.57398066483438015))" ) ) );
//lots of tolerance here - the formulas get quite unstable with small areas due to division by very small floats //lots of tolerance here - the formulas get quite unstable with small areas due to division by very small floats
QGSCOMPARENEAR( calc.measureArea( geom ), 43.183369, 0.02 ); QGSCOMPARENEAR( calc.measureArea( geom ), 43.3280029296875, 0.2 );
} }
QGSTEST_MAIN( TestQgsDistanceArea ) QGSTEST_MAIN( TestQgsDistanceArea )