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# qgis / QGIS

Merge pull request #5089 from nyalldawson/hausdorff

`Expose GEOS Hausdorff distance calculations to QgsGeometry, add expression function`
nyalldawson committed Aug 31, 2017
2 parents 4810c73 + c2f8a82 commit 133d58fa895fe760622a355e0c31beeb68640a1c
 @@ -241,6 +241,47 @@ Returns true if WKB of the geometry is of WKBMulti* type :rtype: float %End double hausdorffDistance( const QgsGeometry &geom ) const; %Docstring Returns the Hausdorff distance between this geometry and ``geom``. This is basically a measure of how similar or dissimilar 2 geometries are. This algorithm is an approximation to the standard Hausdorff distance. This approximation is exact or close enough for a large subset of useful cases. Examples of these are: - computing distance between Linestrings that are roughly parallel to each other, and roughly equal in length. This occurs in matching linear networks. - Testing similarity of geometries. If the default approximate provided by this method is insufficient, use hausdorffDistanceDensify() instead. In case of error -1 will be returned. .. versionadded:: 3.0 .. seealso:: hausdorffDistanceDensify() :rtype: float %End double hausdorffDistanceDensify( const QgsGeometry &geom, double densifyFraction ) const; %Docstring Returns the Hausdorff distance between this geometry and ``geom``. This is basically a measure of how similar or dissimilar 2 geometries are. This function accepts a ``densifyFraction`` argument. The function performs a segment densification before computing the discrete Hausdorff distance. The ``densifyFraction`` parameter sets the fraction by which to densify each segment. Each segment will be split into a number of equal-length subsegments, whose fraction of the total length is closest to the given fraction. This method can be used when the default approximation provided by hausdorffDistance() is not sufficient. Decreasing the ``densifyFraction`` parameter will make the distance returned approach the true Hausdorff distance for the geometries. In case of error -1 will be returned. .. versionadded:: 3.0 .. seealso:: hausdorffDistance() :rtype: float %End QgsPointXY closestVertex( const QgsPointXY &point, int &atVertex /Out/, int &beforeVertex /Out/, int &afterVertex /Out/, double &sqrDist /Out/ ) const; %Docstring :rtype: QgsPointXY @@ -1251,10 +1292,11 @@ Returns an extruded version of this geometry. :rtype: int %End QString error() const; QString lastError() const; %Docstring Returns an error string referring to an error that was produced when this geometry was created. Returns an error string referring to the last error encountered either when this geometry was created or when an operation was performed on the geometry. .. versionadded:: 3.0 :rtype: str
 @@ -0,0 +1,12 @@ { "name": "hausdorff_distance", "type": "function", "description": "Returns the Hausdorff distance between two geometries. This is basically a measure of how similar or dissimilar 2 geometries are, with a lower distance indicating more similar geometries.
The function can be executed with an optional densify fraction argument. If not specified, an appoximation to the standard Hausdorff distance is used. This approximation is exact or close enough for a large subset of useful cases. Examples of these are:

• computing distance between Linestrings that are roughly parallel to each other, and roughly equal in length. This occurs in matching linear networks.
• Testing similarity of geometries.

• If the default approximate provided by this method is insufficient, specify the optional densify fraction argument. Specifying this argument performs a segment densification before computing the discrete Hausdorff distance. The parameter sets the fraction by which to densify each segment. Each segment will be split into a number of equal-length subsegments, whose fraction of the total length is closest to the given fraction. Decreasing the densify fraction parameter will make the distance returned approach the true Hausdorff distance for the geometries.", "arguments": [ {"arg":"geometry a","description":"a geometry"}, {"arg":"geometry b","description":"a geometry"}, {"arg":"densify_fraction","description":"densify fraction amount", "optional":true}], "examples": [ { "expression":"hausdorff_distance( geometry1:= geom_from_wkt('LINESTRING (0 0, 2 1)'),geometry2:=geom_from_wkt('LINESTRING (0 0, 2 0)'))", "returns":"2"}, { "expression":"hausdorff_distance( geom_from_wkt('LINESTRING (130 0, 0 0, 0 150)'),geom_from_wkt('LINESTRING (10 10, 10 150, 130 10)'))", "returns":"14.142135623"}, { "expression":"hausdorff_distance( geom_from_wkt('LINESTRING (130 0, 0 0, 0 150)'),geom_from_wkt('LINESTRING (10 10, 10 150, 130 10)'),0.5)", "returns":"70.0"} ] }
 @@ -53,6 +53,7 @@ QVariant QgsExpressionFunction::run( QgsExpressionNode::NodeList *args, const Qg QVariantList argValues; if ( args ) { int arg = 0; Q_FOREACH ( QgsExpressionNode *n, args->list() ) { QVariant v; @@ -65,10 +66,12 @@ QVariant QgsExpressionFunction::run( QgsExpressionNode::NodeList *args, const Qg { v = n->eval( parent, context ); ENSURE_NO_EVAL_ERROR; if ( QgsExpressionUtils::isNull( v ) && !handlesNull() ) bool defaultParamIsNull = mParameterList.count() > arg && mParameterList.at( arg ).optional() && !mParameterList.at( arg ).defaultValue().isValid(); if ( QgsExpressionUtils::isNull( v ) && !defaultParamIsNull && !handlesNull() ) return QVariant(); // all "normal" functions return NULL, when any QgsExpressionFunction::Parameter is NULL (so coalesce is abnormal) } argValues.append( v ); arg++; } } @@ -2574,6 +2577,27 @@ static QVariant fcnDistance( const QVariantList &values, const QgsExpressionCont QgsGeometry sGeom = QgsExpressionUtils::getGeometry( values.at( 1 ), parent ); return QVariant( fGeom.distance( sGeom ) ); } static QVariant fcnHausdorffDistance( const QVariantList &values, const QgsExpressionContext *, QgsExpression *parent ) { QgsGeometry g1 = QgsExpressionUtils::getGeometry( values.at( 0 ), parent ); QgsGeometry g2 = QgsExpressionUtils::getGeometry( values.at( 1 ), parent ); double res = -1; if ( values.length() == 3 && values.at( 2 ).isValid() ) { double densify = QgsExpressionUtils::getDoubleValue( values.at( 2 ), parent ); densify = qBound( 0.0, densify, 1.0 ); res = g1.hausdorffDistanceDensify( g2, densify ); } else { res = g1.hausdorffDistance( g2 ); } return res > -1 ? QVariant( res ) : QVariant(); } static QVariant fcnIntersection( const QVariantList &values, const QgsExpressionContext *, QgsExpression *parent ) { QgsGeometry fGeom = QgsExpressionUtils::getGeometry( values.at( 0 ), parent ); @@ -4113,6 +4137,8 @@ const QList &QgsExpression::Functions() << new QgsStaticExpressionFunction( QStringLiteral( "convex_hull" ), 1, fcnConvexHull, QStringLiteral( "GeometryGroup" ), QString(), false, QSet(), false, QStringList() << QStringLiteral( "convexHull" ) ) << new QgsStaticExpressionFunction( QStringLiteral( "difference" ), 2, fcnDifference, QStringLiteral( "GeometryGroup" ) ) << new QgsStaticExpressionFunction( QStringLiteral( "distance" ), 2, fcnDistance, QStringLiteral( "GeometryGroup" ) ) << new QgsStaticExpressionFunction( QStringLiteral( "hausdorff_distance" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "geometry1" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "geometry2" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "densify_fraction" ), true ), fcnHausdorffDistance, QStringLiteral( "GeometryGroup" ) ) << new QgsStaticExpressionFunction( QStringLiteral( "intersection" ), 2, fcnIntersection, QStringLiteral( "GeometryGroup" ) ) << new QgsStaticExpressionFunction( QStringLiteral( "sym_difference" ), 2, fcnSymDifference, QStringLiteral( "GeometryGroup" ), QString(), false, QSet(), false, QStringList() << QStringLiteral( "symDifference" ) ) << new QgsStaticExpressionFunction( QStringLiteral( "combine" ), 2, fcnCombine, QStringLiteral( "GeometryGroup" ) )