[processing] Merge lines on dissolve

m-kuhn · m-kuhn · commit a2018debfb8a · 2019-02-22T11:17:32.000+01:00
This is a difference between how polygons and lines are handled on dissolve.
Neighbouring polygons are merged automatically, while lines are collected as
MultiLineString.

With this patch it will be possible to call multipart to singlepart on dissolved
line layers to extract spatially separated parts of a linestring.
diff --git a/src/analysis/processing/qgsalgorithmdissolve.cpp b/src/analysis/processing/qgsalgorithmdissolve.cpp
@@ -227,6 +227,8 @@ QVariantMap QgsDissolveAlgorithm::processAlgorithm( const QVariantMap &parameter
       for ( const auto &p : parts )
       {
         result = QgsGeometry::unaryUnion( QVector< QgsGeometry >() << result << p );
+        if ( QgsWkbTypes::flatType( result.wkbType() ) == QgsWkbTypes::LineString )
+          result = result.mergeLines();
         if ( feedback->isCanceled() )
           return result;
       }

Original file line number	Diff line number	Diff line change
`@@ -227,6 +227,8 @@ QVariantMap QgsDissolveAlgorithm::processAlgorithm( const QVariantMap &parameter`
`227`	`227`	`for ( const auto &p : parts )`
`228`	`228`	`{`
`229`	`229`	`result = QgsGeometry::unaryUnion( QVector< QgsGeometry >() << result << p );`
	`230`	`+ if ( QgsWkbTypes::flatType( result.wkbType() ) == QgsWkbTypes::LineString )`
	`231`	`+ result = result.mergeLines();`
`230`	`232`	`if ( feedback->isCanceled() )`
`231`	`233`	`return result;`
`232`	`234`	`}`