[FEATURE[processing] New algorithm to compute geometry by expression

This algorithm updates existing geometries (or creates new geometries) for input features by use of a QGIS expression. This allows complex geometry modifications which can utilise all the flexibility of the QGIS expression engine to manipulate and create geometries for output features.
qgis · Nov 2, 2016 · f65e770 · f65e770
1 parent 5e3bef7
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diff --git a/python/plugins/processing/algs/help/qgis.yaml b/python/plugins/processing/algs/help/qgis.yaml
@@ -201,6 +201,11 @@ qgis:fixeddistancebuffer: >
 qgis:frequencyanalysis: >
   This algorithms generates a table with frequency analysis of the values of a selected attribute from an input vector layer
 
+qgis:geometrybyexpression: >
+  This algorithm updates existing geometries (or creates new geometries) for input features by use of a QGIS expression. This allows complex geometry modifications which can utilise all the flexibility of the QGIS expression engine to manipulate and create geometries for output features.
+
+  For help with QGIS expression functions, see the inbuilt help for specific functions which is available in the expression builder.
+
 qgis:generatepointspixelcentroidsalongline:
 
 

diff --git a/python/plugins/processing/algs/qgis/GeometryByExpression.py b/python/plugins/processing/algs/qgis/GeometryByExpression.py
@@ -0,0 +1,129 @@
+# -*- coding: utf-8 -*-
+
+"""
+***************************************************************************
+    GeometryByExpression.py
+    -----------------------
+    Date                 : October 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__ = 'October 2016'
+__copyright__ = '(C) 2016, Nyall Dawson'
+
+# This will get replaced with a git SHA1 when you do a git archive323
+
+__revision__ = '$Format:%H$'
+
+from qgis.core import QgsWkbTypes, QgsExpression, QgsExpressionContext, QgsExpressionContextUtils, QgsGeometry
+
+from processing.core.GeoAlgorithm import GeoAlgorithm
+from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
+from processing.core.ProcessingLog import ProcessingLog
+from processing.core.parameters import ParameterVector, ParameterSelection, ParameterBoolean, ParameterString
+from processing.core.outputs import OutputVector
+from processing.tools import dataobjects, vector
+
+
+class GeometryByExpression(GeoAlgorithm):
+
+    INPUT_LAYER = 'INPUT_LAYER'
+    OUTPUT_LAYER = 'OUTPUT_LAYER'
+    OUTPUT_GEOMETRY = 'OUTPUT_GEOMETRY'
+    WITH_Z = 'WITH_Z'
+    WITH_M = 'WITH_M'
+    EXPRESSION = 'EXPRESSION'
+
+    def defineCharacteristics(self):
+        self.name, self.i18n_name = self.trAlgorithm('Geometry by expression')
+        self.group, self.i18n_group = self.trAlgorithm('Vector geometry tools')
+
+        self.addParameter(ParameterVector(self.INPUT_LAYER,
+                                          self.tr('Input layer')))
+
+        self.geometry_types = [self.tr('Polygon'),
+                               'Line',
+                               'Point']
+        self.addParameter(ParameterSelection(
+            self.OUTPUT_GEOMETRY,
+            self.tr('Output geometry type'),
+            self.geometry_types, default=0))
+        self.addParameter(ParameterBoolean(self.WITH_Z,
+                                           self.tr('Output geometry has z dimension'), False))
+        self.addParameter(ParameterBoolean(self.WITH_M,
+                                           self.tr('Output geometry has m values'), False))
+
+        self.addParameter(ParameterString(self.EXPRESSION,
+                                          self.tr("Geometry expression"), '$geometry'))
+
+        self.addOutput(OutputVector(self.OUTPUT_LAYER, self.tr('Modified geometry')))
+
+    def processAlgorithm(self, progress):
+        layer = dataobjects.getObjectFromUri(
+            self.getParameterValue(self.INPUT_LAYER))
+
+        geometry_type = self.getParameterValue(self.OUTPUT_GEOMETRY)
+        wkb_type = None
+        if geometry_type == 0:
+            wkb_type = QgsWkbTypes.Polygon
+        elif geometry_type == 1:
+            wkb_type = QgsWkbTypes.LineString
+        else:
+            wkb_type = QgsWkbTypes.Point
+        if self.getParameterValue(self.WITH_Z):
+            wkb_type = QgsWkbTypes.addZ(wkb_type)
+        if self.getParameterValue(self.WITH_M):
+            wkb_type = QgsWkbTypes.addM(wkb_type)
+
+        writer = self.getOutputFromName(
+            self.OUTPUT_LAYER).getVectorWriter(
+                layer.fields(),
+                wkb_type,
+                layer.crs())
+
+        expression = QgsExpression(self.getParameterValue(self.EXPRESSION))
+        if expression.hasParserError():
+            raise GeoAlgorithmExecutionException(expression.parserErrorString())
+
+        exp_context = QgsExpressionContext()
+        exp_context.appendScope(QgsExpressionContextUtils.globalScope())
+        exp_context.appendScope(QgsExpressionContextUtils.projectScope())
+        exp_context.appendScope(QgsExpressionContextUtils.layerScope(layer))
+
+        if not expression.prepare(exp_context):
+            raise GeoAlgorithmExecutionException(
+                self.tr('Evaluation error: %s' % expression.evalErrorString()))
+
+        features = vector.features(layer)
+        total = 100.0 / len(features)
+        for current, input_feature in enumerate(features):
+            output_feature = input_feature
+
+            exp_context.setFeature(input_feature)
+            value = expression.evaluate(exp_context)
+            if expression.hasEvalError():
+                raise GeoAlgorithmExecutionException(
+                    self.tr('Evaluation error: %s' % expression.evalErrorString()))
+
+            if not value:
+                output_feature.setGeometry(QgsGeometry())
+            else:
+                if not isinstance(value, QgsGeometry):
+                    raise GeoAlgorithmExecutionException(
+                        self.tr('{} is not a geometry').format(value))
+                output_feature.setGeometry(value)
+
+            writer.addFeature(output_feature)
+            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
@@ -174,6 +174,7 @@
 from .RemoveNullGeometry import RemoveNullGeometry
 from .ExtendLines import ExtendLines
 from .ExtractSpecificNodes import ExtractSpecificNodes
+from .GeometryByExpression import GeometryByExpression
 
 pluginPath = os.path.normpath(os.path.join(
     os.path.split(os.path.dirname(__file__))[0], os.pardir))
@@ -236,7 +237,7 @@ def __init__(self):
                         IdwInterpolationZValue(), IdwInterpolationAttribute(),
                         TinInterpolationZValue(), TinInterpolationAttribute(),
                         RemoveNullGeometry(), ExtractByExpression(), ExtendLines(),
-                        ExtractSpecificNodes()
+                        ExtractSpecificNodes(), GeometryByExpression()
                         ]
 
         if hasMatplotlib:

diff --git a/python/plugins/processing/tests/testdata/expected/geometry_by_expression_line.gfs b/python/plugins/processing/tests/testdata/expected/geometry_by_expression_line.gfs
@@ -0,0 +1,16 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>geometry_by_expression_line</Name>
+    <ElementPath>geometry_by_expression_line</ElementPath>
+    <!--LINESTRING-->
+    <GeometryType>2</GeometryType>
+    <SRSName>EPSG:4326</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>7</FeatureCount>
+      <ExtentXMin>0.00000</ExtentXMin>
+      <ExtentXMax>12.00000</ExtentXMax>
+      <ExtentYMin>-2.00000</ExtentYMin>
+      <ExtentYMax>6.00000</ExtentYMax>
+    </DatasetSpecificInfo>
+  </GMLFeatureClass>
+</GMLFeatureClassList>
diff --git a/python/plugins/processing/tests/testdata/expected/geometry_by_expression_line.gml b/python/plugins/processing/tests/testdata/expected/geometry_by_expression_line.gml
@@ -0,0 +1,48 @@
+<?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>0</gml:X><gml:Y>-2</gml:Y></gml:coord>
+      <gml:coord><gml:X>12</gml:X><gml:Y>6</gml:Y></gml:coord>
+    </gml:Box>
+  </gml:boundedBy>
+
+  <gml:featureMember>
+    <ogr:geometry_by_expression_line fid="lines.0">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>7,3 10,3 10,4 12,6</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:geometry_by_expression_line>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_line fid="lines.1">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>0,0 2,0</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:geometry_by_expression_line>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_line fid="lines.2">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>3,1 3,3 4,3 4,4</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:geometry_by_expression_line>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_line fid="lines.3">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>4,2 6,2</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:geometry_by_expression_line>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_line fid="lines.4">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>8,-2 11,-2</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:geometry_by_expression_line>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_line fid="lines.5">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>7,-2 11,2</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:geometry_by_expression_line>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_line fid="lines.6">
+    </ogr:geometry_by_expression_line>
+  </gml:featureMember>
+</ogr:FeatureCollection>
diff --git a/python/plugins/processing/tests/testdata/expected/geometry_by_expression_point.gfs b/python/plugins/processing/tests/testdata/expected/geometry_by_expression_point.gfs
@@ -0,0 +1,16 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>geometry_by_expression_point</Name>
+    <ElementPath>geometry_by_expression_point</ElementPath>
+    <!--POINT-->
+    <GeometryType>1</GeometryType>
+    <SRSName>EPSG:4326</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>9</FeatureCount>
+      <ExtentXMin>1.00000</ExtentXMin>
+      <ExtentXMax>9.00000</ExtentXMax>
+      <ExtentYMin>-4.00000</ExtentYMin>
+      <ExtentYMax>4.00000</ExtentYMax>
+    </DatasetSpecificInfo>
+  </GMLFeatureClass>
+</GMLFeatureClassList>
diff --git a/python/plugins/processing/tests/testdata/expected/geometry_by_expression_point.gml b/python/plugins/processing/tests/testdata/expected/geometry_by_expression_point.gml
@@ -0,0 +1,59 @@
+<?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>-4</gml:Y></gml:coord>
+      <gml:coord><gml:X>9</gml:X><gml:Y>4</gml:Y></gml:coord>
+    </gml:Box>
+  </gml:boundedBy>
+
+  <gml:featureMember>
+    <ogr:geometry_by_expression_point fid="points.0">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>2,2</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:geometry_by_expression_point>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_point fid="points.1">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>4,4</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:geometry_by_expression_point>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_point fid="points.2">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>3,3</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:geometry_by_expression_point>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_point fid="points.3">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>6,3</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:geometry_by_expression_point>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_point fid="points.4">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>5,2</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:geometry_by_expression_point>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_point fid="points.5">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>1,-4</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:geometry_by_expression_point>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_point fid="points.6">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>9,0</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:geometry_by_expression_point>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_point fid="points.7">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>8,0</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:geometry_by_expression_point>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_point fid="points.8">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>1,0</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:geometry_by_expression_point>
+  </gml:featureMember>
+</ogr:FeatureCollection>
diff --git a/python/plugins/processing/tests/testdata/expected/geometry_by_expression_poly.gfs b/python/plugins/processing/tests/testdata/expected/geometry_by_expression_poly.gfs
@@ -0,0 +1,32 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>geometry_by_expression_poly</Name>
+    <ElementPath>geometry_by_expression_poly</ElementPath>
+    <!--POINT-->
+    <GeometryType>1</GeometryType>
+    <SRSName>EPSG:4326</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>6</FeatureCount>
+      <ExtentXMin>1.65385</ExtentXMin>
+      <ExtentXMax>9.00000</ExtentXMax>
+      <ExtentYMin>0.00000</ExtentYMin>
+      <ExtentYMax>6.50000</ExtentYMax>
+    </DatasetSpecificInfo>
+    <PropertyDefn>
+      <Name>name</Name>
+      <ElementPath>name</ElementPath>
+      <Type>String</Type>
+      <Width>5</Width>
+    </PropertyDefn>
+    <PropertyDefn>
+      <Name>intval</Name>
+      <ElementPath>intval</ElementPath>
+      <Type>Integer</Type>
+    </PropertyDefn>
+    <PropertyDefn>
+      <Name>floatval</Name>
+      <ElementPath>floatval</ElementPath>
+      <Type>Real</Type>
+    </PropertyDefn>
+  </GMLFeatureClass>
+</GMLFeatureClassList>
diff --git a/python/plugins/processing/tests/testdata/expected/geometry_by_expression_poly.gml b/python/plugins/processing/tests/testdata/expected/geometry_by_expression_poly.gml
@@ -0,0 +1,58 @@
+<?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>1.653846153846154</gml:X><gml:Y>0</gml:Y></gml:coord>
+      <gml:coord><gml:X>9</gml:X><gml:Y>6.5</gml:Y></gml:coord>
+    </gml:Box>
+  </gml:boundedBy>
+
+  <gml:featureMember>
+    <ogr:geometry_by_expression_poly fid="polys.0">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>1.653846153846154,2.115384615384615</gml:coordinates></gml:Point></ogr:geometryProperty>
+      <ogr:name>aaaaa</ogr:name>
+      <ogr:intval>33</ogr:intval>
+      <ogr:floatval>44.123456</ogr:floatval>
+    </ogr:geometry_by_expression_poly>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_poly fid="polys.1">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>6.0,5.333333333333333</gml:coordinates></gml:Point></ogr:geometryProperty>
+      <ogr:name>Aaaaa</ogr:name>
+      <ogr:intval>-33</ogr:intval>
+      <ogr:floatval>0</ogr:floatval>
+    </ogr:geometry_by_expression_poly>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_poly fid="polys.2">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>3.5,6.5</gml:coordinates></gml:Point></ogr:geometryProperty>
+      <ogr:name>bbaaa</ogr:name>
+      <ogr:floatval>0.123</ogr:floatval>
+    </ogr:geometry_by_expression_poly>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_poly fid="polys.3">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>9,0</gml:coordinates></gml:Point></ogr:geometryProperty>
+      <ogr:name>ASDF</ogr:name>
+      <ogr:intval>0</ogr:intval>
+    </ogr:geometry_by_expression_poly>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_poly fid="polys.4">
+      <ogr:intval>120</ogr:intval>
+      <ogr:floatval>-100291.43213</ogr:floatval>
+    </ogr:geometry_by_expression_poly>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:geometry_by_expression_poly fid="polys.5">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>5.080459770114943,0.781609195402299</gml:coordinates></gml:Point></ogr:geometryProperty>
+      <ogr:name>elim</ogr:name>
+      <ogr:intval>2</ogr:intval>
+      <ogr:floatval>3.33</ogr:floatval>
+    </ogr:geometry_by_expression_poly>
+  </gml:featureMember>
+</ogr:FeatureCollection>