[FEATURE][processing] New algorithm for merging connected lines

This algorithm joins all connected parts of MultiLineString geometries into single LineString geometries. If any parts of the input MultiLineString geometries are not connected, the resultant geometry will be a MultiLineString containing any lines which could be merged and any non-connected line parts. (cherry-picked from 30fcaed)
qgis · Aug 9, 2016 · 299037a · 299037a
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diff --git a/python/plugins/processing/algs/help/qgis.yaml b/python/plugins/processing/algs/help/qgis.yaml
@@ -225,6 +225,11 @@ qgis:meancoordinates: >
 
   If an attribute is selected in the  <Unique ID  field> parameters, features will be grouped according to values in this field. Instead of a single point with the center of mass of the whole layer, the  output layer will contain a center of mass for the features in each category.
 
+qgis:mergelines: >
+  This algorithm joins all connected parts of MultiLineString geometries into single LineString geometries.
+
+  If any parts of the input MultiLineString geometries are not connected, the resultant geometry will be a MultiLineString containing any lines which could be merged and any non-connected line parts.
+
 qgis:mergevectorlayers: >
   This algorithm combines two vector layer of the same geometry type into a single one.
 

diff --git a/python/plugins/processing/algs/qgis/MergeLines.py b/python/plugins/processing/algs/qgis/MergeLines.py
@@ -0,0 +1,89 @@
+# -*- coding: utf-8 -*-
+
+"""
+***************************************************************************
+    Smooth.py
+    ---------
+    Date                 : July 2016
+    Copyright            : (C) 2016 by Nyall Dawson
+    Email                : nyall dot dawson at gmail dot com
+***************************************************************************
+*                                                                         *
+*   This program is free software; you can redistribute it and/or modify  *
+*   it under the terms of the GNU General Public License as published by  *
+*   the Free Software Foundation; either version 2 of the License, or     *
+*   (at your option) any later version.                                   *
+*                                                                         *
+***************************************************************************
+"""
+
+__author__ = 'Nyall Dawson'
+__date__ = 'July 2016'
+__copyright__ = '(C) 2016, Nyall Dawson'
+
+# This will get replaced with a git SHA1 when you do a git archive323
+
+__revision__ = '$Format:%H$'
+
+import os
+
+from qgis.core import QgsFeature, QgsGeometry
+
+from qgis.PyQt.QtGui import QIcon
+
+from processing.core.GeoAlgorithm import GeoAlgorithm
+from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
+from processing.core.parameters import ParameterVector
+from processing.core.outputs import OutputVector
+from processing.tools import dataobjects, vector
+
+pluginPath = os.path.split(os.path.split(os.path.dirname(__file__))[0])[0]
+
+
+class MergeLines(GeoAlgorithm):
+
+    INPUT_LAYER = 'INPUT_LAYER'
+    OUTPUT_LAYER = 'OUTPUT_LAYER'
+
+    def getIcon(self):
+        return QIcon(os.path.join(pluginPath, 'images', 'ftools', 'to_lines.png'))
+
+    def defineCharacteristics(self):
+        self.name, self.i18n_name = self.trAlgorithm('Merge lines')
+        self.group, self.i18n_group = self.trAlgorithm('Vector geometry tools')
+
+        self.addParameter(ParameterVector(self.INPUT_LAYER,
+                                          self.tr('Input layer'), [ParameterVector.VECTOR_TYPE_LINE]))
+        self.addOutput(OutputVector(self.OUTPUT_LAYER, self.tr('Merged')))
+
+    def processAlgorithm(self, progress):
+        layer = dataobjects.getObjectFromUri(
+            self.getParameterValue(self.INPUT_LAYER))
+
+        writer = self.getOutputFromName(
+            self.OUTPUT_LAYER).getVectorWriter(
+                layer.fields().toList(),
+                layer.wkbType(),
+                layer.crs())
+
+        features = vector.features(layer)
+        total = 100.0 / len(features)
+
+        for current, inFeat in enumerate(features):
+            outFeat = QgsFeature()
+            attrs = inFeat.attributes()
+            outFeat.setAttributes(attrs)
+
+            inGeom = QgsGeometry(inFeat.constGeometry())
+            if inGeom:
+                outGeom = inGeom.mergeLines()
+                if outGeom is None:
+                    raise GeoAlgorithmExecutionException(
+                        self.tr('Error merging lines'))
+
+                outFeat.setGeometry(outGeom)
+
+            writer.addFeature(outFeat)
+            progress.setPercentage(int(current * total))
+
+        del writer
diff --git a/python/plugins/processing/algs/qgis/QGISAlgorithmProvider.py b/python/plugins/processing/algs/qgis/QGISAlgorithmProvider.py
@@ -146,6 +146,7 @@
 from .DefineProjection import DefineProjection
 from .RectanglesOvalsDiamondsVariable import RectanglesOvalsDiamondsVariable
 from .RectanglesOvalsDiamondsFixed import RectanglesOvalsDiamondsFixed
+from .MergeLines import MergeLines
 
 pluginPath = os.path.normpath(os.path.join(
     os.path.split(os.path.dirname(__file__))[0], os.pardir))
@@ -197,7 +198,7 @@ def __init__(self):
                         CheckValidity(), OrientedMinimumBoundingBox(), Smooth(),
                         ReverseLineDirection(), SpatialIndex(), DefineProjection(),
                         RectanglesOvalsDiamondsVariable(),
-                        RectanglesOvalsDiamondsFixed()
+                        RectanglesOvalsDiamondsFixed(), MergeLines()
                         ]
 
         if hasMatplotlib:

diff --git a/python/plugins/processing/tests/testdata/expected/merge_lines.gml b/python/plugins/processing/tests/testdata/expected/merge_lines.gml
@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ogr:FeatureCollection
+     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+     xsi:schemaLocation="http://ogr.maptools.org/ merge_lines.xsd"
+     xmlns:ogr="http://ogr.maptools.org/"
+     xmlns:gml="http://www.opengis.net/gml">
+  <gml:boundedBy>
+    <gml:Box>
+      <gml:coord><gml:X>-1</gml:X><gml:Y>-1</gml:Y></gml:coord>
+      <gml:coord><gml:X>5.58042226487524</gml:X><gml:Y>4.119769673704415</gml:Y></gml:coord>
+    </gml:Box>
+  </gml:boundedBy>
+
+  <gml:featureMember>
+    <ogr:merge_lines fid="lines.1">
+      <ogr:geometryProperty><gml:MultiLineString srsName="EPSG:4326"><gml:lineStringMember><gml:LineString><gml:coordinates>-1,-1 1,-1</gml:coordinates></gml:LineString></gml:lineStringMember></gml:MultiLineString></ogr:geometryProperty>
+    </ogr:merge_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:merge_lines fid="lines.2">
+      <ogr:geometryProperty><gml:MultiLineString srsName="EPSG:4326"><gml:lineStringMember><gml:LineString><gml:coordinates>3,1 5,1 5.024184261036468,2.414779270633399</gml:coordinates></gml:LineString></gml:lineStringMember></gml:MultiLineString></ogr:geometryProperty>
+    </ogr:merge_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:merge_lines fid="lines.3">
+    </ogr:merge_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:merge_lines fid="lines.4">
+      <ogr:geometryProperty><gml:MultiLineString srsName="EPSG:4326"><gml:lineStringMember><gml:LineString><gml:coordinates>2,0 2,2 3,2 3,3 5.58042226487524,2.946833013435702</gml:coordinates></gml:LineString></gml:lineStringMember><gml:lineStringMember><gml:LineString><gml:coordinates>2.944337811900192,4.04721689059501 5.459500959692898,4.119769673704415</gml:coordinates></gml:LineString></gml:lineStringMember></gml:MultiLineString></ogr:geometryProperty>
+    </ogr:merge_lines>
+  </gml:featureMember>
+</ogr:FeatureCollection>
diff --git a/python/plugins/processing/tests/testdata/multilines.gfs b/python/plugins/processing/tests/testdata/multilines.gfs
@@ -0,0 +1,15 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>multilines</Name>
+    <ElementPath>multilines</ElementPath>
+    <GeometryType>5</GeometryType>
+    <SRSName>EPSG:4326</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>4</FeatureCount>
+      <ExtentXMin>-1.00000</ExtentXMin>
+      <ExtentXMax>5.58042</ExtentXMax>
+      <ExtentYMin>-1.00000</ExtentYMin>
+      <ExtentYMax>4.11977</ExtentYMax>
+    </DatasetSpecificInfo>
+  </GMLFeatureClass>
+</GMLFeatureClassList>
diff --git a/python/plugins/processing/tests/testdata/multilines.gml b/python/plugins/processing/tests/testdata/multilines.gml
@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ogr:FeatureCollection
+     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+     xsi:schemaLocation=""
+     xmlns:ogr="http://ogr.maptools.org/"
+     xmlns:gml="http://www.opengis.net/gml">
+  <gml:boundedBy>
+    <gml:Box>
+      <gml:coord><gml:X>-1</gml:X><gml:Y>-1</gml:Y></gml:coord>
+      <gml:coord><gml:X>5.58042226487524</gml:X><gml:Y>4.119769673704415</gml:Y></gml:coord>
+    </gml:Box>
+  </gml:boundedBy>
+
+  <gml:featureMember>
+    <ogr:multilines fid="lines.1">
+      <ogr:geometryProperty><gml:MultiLineString srsName="EPSG:4326"><gml:lineStringMember><gml:LineString><gml:coordinates>-1,-1 1,-1</gml:coordinates></gml:LineString></gml:lineStringMember></gml:MultiLineString></ogr:geometryProperty>
+    </ogr:multilines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:multilines fid="lines.2">
+      <ogr:geometryProperty><gml:MultiLineString srsName="EPSG:4326"><gml:lineStringMember><gml:LineString><gml:coordinates>3,1 5,1</gml:coordinates></gml:LineString></gml:lineStringMember><gml:lineStringMember><gml:LineString><gml:coordinates>5.024184261036468,2.414779270633399 5,1</gml:coordinates></gml:LineString></gml:lineStringMember></gml:MultiLineString></ogr:geometryProperty>
+    </ogr:multilines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:multilines fid="lines.3">
+    </ogr:multilines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:multilines fid="lines.4">
+      <ogr:geometryProperty><gml:MultiLineString srsName="EPSG:4326"><gml:lineStringMember><gml:LineString><gml:coordinates>2,0 2,2 3,2 3,3</gml:coordinates></gml:LineString></gml:lineStringMember><gml:lineStringMember><gml:LineString><gml:coordinates>2.944337811900192,4.04721689059501 5.459500959692898,4.119769673704415</gml:coordinates></gml:LineString></gml:lineStringMember><gml:lineStringMember><gml:LineString><gml:coordinates>3,3 5.58042226487524,2.946833013435702</gml:coordinates></gml:LineString></gml:lineStringMember></gml:MultiLineString></ogr:geometryProperty>
+    </ogr:multilines>
+  </gml:featureMember>
+</ogr:FeatureCollection>
diff --git a/python/plugins/processing/tests/testdata/qgis_algorithm_tests.yaml b/python/plugins/processing/tests/testdata/qgis_algorithm_tests.yaml
@@ -306,3 +306,15 @@ tests:
         compare:
           geometry:
             precision: 7
+
+  - algorithm: qgis:mergelines
+    name: Merge lines algorithm
+    params:
+      INPUT_LAYER:
+        name: multilines.gml
+        type: vector
+    results:
+      OUTPUT_LAYER:
+        name: expected/merge_lines.gml
+        type: vector
+