[FEATURE][processing] Add choice of simplification method to simplify

This change allows users to choose which method to use when running the simplify geometries algorithm, with choices of the existing distance based (Douglas Peucker) algorithm, area based (Visvalingam) algorithm and snap-to-grid. Visvaligam in particular usually results in more cartographically pleasing simplification over the standard distance based methods.
qgis · Aug 31, 2016 · 56b77db · 56b77db
1 parent fbd6618
commit 56b77db
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Showing 9 changed files with 193 additions and 2 deletions.
diff --git a/python/plugins/processing/algs/help/qgis.yaml b/python/plugins/processing/algs/help/qgis.yaml
@@ -429,6 +429,8 @@ qgis:setstyleforvectorlayer: >
 qgis:simplifygeometries: >
   This algorithm simplifies the geometries in a line or polygon layer. It creates a new layer with the same features as the ones in the input layer, but with geometries containing a lower number of vertices.
 
+  The algorithm gives a choice of simplification methods, including distance based (the "Douglas-Peucker" algorithm), area based ("Visvalingam" algorithm) and snapping geometries to grid.
+
 qgis:singlepartstomultipart:
 
 

diff --git a/python/plugins/processing/algs/qgis/SimplifyGeometries.py b/python/plugins/processing/algs/qgis/SimplifyGeometries.py
@@ -29,12 +29,13 @@
 
 from qgis.PyQt.QtGui import QIcon
 
-from qgis.core import Qgis, QgsFeature, QgsGeometry, QgsWkbTypes
+from qgis.core import Qgis, QgsFeature, QgsGeometry, QgsWkbTypes, QgsMapToPixelSimplifier
 
 from processing.core.GeoAlgorithm import GeoAlgorithm
 from processing.core.ProcessingLog import ProcessingLog
 from processing.core.parameters import ParameterVector
 from processing.core.parameters import ParameterNumber
+from processing.core.parameters import ParameterSelection
 from processing.core.outputs import OutputVector
 from processing.tools import dataobjects, vector
 
@@ -46,6 +47,7 @@ class SimplifyGeometries(GeoAlgorithm):
     INPUT = 'INPUT'
     TOLERANCE = 'TOLERANCE'
     OUTPUT = 'OUTPUT'
+    METHOD = 'METHOD'
 
     def getIcon(self):
         return QIcon(os.path.join(pluginPath, 'images', 'ftools', 'simplify.png'))
@@ -57,6 +59,13 @@ def defineCharacteristics(self):
         self.addParameter(ParameterVector(self.INPUT,
                                           self.tr('Input layer'),
                                           [ParameterVector.VECTOR_TYPE_POLYGON, ParameterVector.VECTOR_TYPE_LINE]))
+        self.methods = [self.tr('Distance (Douglas-Peucker)'),
+                        'Snap to grid',
+                        'Area (Visvalingam)']
+        self.addParameter(ParameterSelection(
+            self.METHOD,
+            self.tr('Simplification method'),
+            self.methods, default=0))
         self.addParameter(ParameterNumber(self.TOLERANCE,
                                           self.tr('Tolerance'), 0.0, 10000000.0, 1.0))
 
@@ -65,6 +74,7 @@ def defineCharacteristics(self):
     def processAlgorithm(self, progress):
         layer = dataobjects.getObjectFromUri(self.getParameterValue(self.INPUT))
         tolerance = self.getParameterValue(self.TOLERANCE)
+        method = self.getParameterValue(self.METHOD)
 
         pointsBefore = 0
         pointsAfter = 0
@@ -74,12 +84,21 @@ def processAlgorithm(self, progress):
 
         features = vector.features(layer)
         total = 100.0 / len(features)
+
+        if method != 0:
+            simplifier = QgsMapToPixelSimplifier(QgsMapToPixelSimplifier.SimplifyGeometry, tolerance, method)
+
         for current, input_feature in enumerate(features):
             out_feature = input_feature
             if input_feature.geometry():
                 input_geometry = input_feature.geometry()
                 pointsBefore += input_geometry.geometry().nCoordinates()
-                output_geometry = input_geometry.simplify(tolerance)
+
+                if method == 0: # distance
+                    output_geometry = input_geometry.simplify(tolerance)
+                else:
+                    output_geometry = simplifier.simplify(input_geometry)
+
                 pointsAfter += output_geometry.geometry().nCoordinates()
                 out_feature.setGeometry(output_geometry)
             writer.addFeature(out_feature)

diff --git a/python/plugins/processing/tests/testdata/expected/simplify_grid_lines.gfs b/python/plugins/processing/tests/testdata/expected/simplify_grid_lines.gfs
@@ -0,0 +1,15 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>simplify_grid_lines</Name>
+    <ElementPath>simplify_grid_lines</ElementPath>
+    <GeometryType>2</GeometryType>
+    <SRSName>EPSG:4326</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>4</FeatureCount>
+      <ExtentXMin>-0.08703</ExtentXMin>
+      <ExtentXMax>10.63163</ExtentXMax>
+      <ExtentYMin>-0.26248</ExtentYMin>
+      <ExtentYMax>4.98546</ExtentYMax>
+    </DatasetSpecificInfo>
+  </GMLFeatureClass>
+</GMLFeatureClassList>
diff --git a/python/plugins/processing/tests/testdata/expected/simplify_grid_lines.gml b/python/plugins/processing/tests/testdata/expected/simplify_grid_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=""
+     xmlns:ogr="http://ogr.maptools.org/"
+     xmlns:gml="http://www.opengis.net/gml">
+  <gml:boundedBy>
+    <gml:Box>
+      <gml:coord><gml:X>-0.08703339882121899</gml:X><gml:Y>-0.262475442043224</gml:Y></gml:coord>
+      <gml:coord><gml:X>10.63163064833006</gml:X><gml:Y>4.985461689587426</gml:Y></gml:coord>
+    </gml:Box>
+  </gml:boundedBy>
+
+  <gml:featureMember>
+    <ogr:simplify_grid_lines fid="1">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>-0.062278978388999,4.985461689587426 5.606483300589391,4.985461689587426</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:simplify_grid_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:simplify_grid_lines fid="3">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>-0.087033398821219,2.782318271119842 2.314145383104125,2.757563850687622 7.388801571709235,4.713163064833005 9.789980353634579,2.757563850687622 10.631630648330059,2.757563850687622</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:simplify_grid_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:simplify_grid_lines fid="2">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>0.061493123772101,-0.237721021611003 1.967583497053045,-0.262475442043224 4.34400785854617,2.262475442043221 6.448133595284873,-0.262475442043224 10.606876227897841,-0.188212180746563</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:simplify_grid_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:simplify_grid_lines fid="4">
+    </ogr:simplify_grid_lines>
+  </gml:featureMember>
+</ogr:FeatureCollection>
diff --git a/python/plugins/processing/tests/testdata/expected/simplify_vis_lines.gfs b/python/plugins/processing/tests/testdata/expected/simplify_vis_lines.gfs
@@ -0,0 +1,15 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>simplify_vis_lines</Name>
+    <ElementPath>simplify_vis_lines</ElementPath>
+    <GeometryType>2</GeometryType>
+    <SRSName>EPSG:4326</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>4</FeatureCount>
+      <ExtentXMin>-0.08703</ExtentXMin>
+      <ExtentXMax>10.63163</ExtentXMax>
+      <ExtentYMin>-0.26248</ExtentYMin>
+      <ExtentYMax>4.98546</ExtentYMax>
+    </DatasetSpecificInfo>
+  </GMLFeatureClass>
+</GMLFeatureClassList>
diff --git a/python/plugins/processing/tests/testdata/expected/simplify_vis_lines.gml b/python/plugins/processing/tests/testdata/expected/simplify_vis_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=""
+     xmlns:ogr="http://ogr.maptools.org/"
+     xmlns:gml="http://www.opengis.net/gml">
+  <gml:boundedBy>
+    <gml:Box>
+      <gml:coord><gml:X>-0.08703339882121899</gml:X><gml:Y>-0.262475442043224</gml:Y></gml:coord>
+      <gml:coord><gml:X>10.63163064833006</gml:X><gml:Y>4.985461689587426</gml:Y></gml:coord>
+    </gml:Box>
+  </gml:boundedBy>
+
+  <gml:featureMember>
+    <ogr:simplify_vis_lines fid="1">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>-0.062278978388999,4.985461689587426 5.606483300589391,4.985461689587426</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:simplify_vis_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:simplify_vis_lines fid="3">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>-0.087033398821219,2.782318271119842 5.284675834970531,2.782318271119842 7.388801571709235,4.713163064833005 10.631630648330059,2.757563850687622</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:simplify_vis_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:simplify_vis_lines fid="2">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>0.061493123772101,-0.237721021611003 1.967583497053045,-0.262475442043224 4.34400785854617,2.262475442043221 6.448133595284873,-0.262475442043224 10.606876227897841,-0.188212180746563</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:simplify_vis_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:simplify_vis_lines fid="4">
+    </ogr:simplify_vis_lines>
+  </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
@@ -939,3 +939,29 @@ tests:
       OUTPUT:
         name: expected/simplify_multilines.gml
         type: vector
+
+  - algorithm: qgis:simplifygeometries
+    name: Simplify (visval)
+    params:
+      INPUT:
+        name: simplify_lines.gml
+        type: vector
+      METHOD: '2'
+      TOLERANCE: 1.0
+    results:
+      OUTPUT:
+        name: expected/simplify_vis_lines.gml
+        type: vector
+
+  - algorithm: qgis:simplifygeometries
+    name: Simplify (grid)
+    params:
+      INPUT:
+        name: simplify_lines.gml
+        type: vector
+      METHOD: '1'
+      TOLERANCE: 5.0
+    results:
+      OUTPUT:
+        name: expected/simplify_grid_lines.gml
+        type: vector
diff --git a/python/plugins/processing/tests/testdata/simplify_lines.gfs b/python/plugins/processing/tests/testdata/simplify_lines.gfs
@@ -0,0 +1,15 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>simplify_lines</Name>
+    <ElementPath>simplify_lines</ElementPath>
+    <GeometryType>2</GeometryType>
+    <SRSName>EPSG:4326</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>4</FeatureCount>
+      <ExtentXMin>-0.08703</ExtentXMin>
+      <ExtentXMax>10.63163</ExtentXMax>
+      <ExtentYMin>-0.26248</ExtentYMin>
+      <ExtentYMax>4.98546</ExtentYMax>
+    </DatasetSpecificInfo>
+  </GMLFeatureClass>
+</GMLFeatureClassList>
diff --git a/python/plugins/processing/tests/testdata/simplify_lines.gml b/python/plugins/processing/tests/testdata/simplify_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=""
+     xmlns:ogr="http://ogr.maptools.org/"
+     xmlns:gml="http://www.opengis.net/gml">
+  <gml:boundedBy>
+    <gml:Box>
+      <gml:coord><gml:X>-0.08703339882121885</gml:X><gml:Y>-0.2624754420432236</gml:Y></gml:coord>
+      <gml:coord><gml:X>10.63163064833006</gml:X><gml:Y>4.985461689587426</gml:Y></gml:coord>
+    </gml:Box>
+  </gml:boundedBy>
+
+  <gml:featureMember>
+    <ogr:simplify_lines fid="1">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>-0.062278978388999,4.985461689587426 5.606483300589391,4.985461689587426</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:simplify_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:simplify_lines fid="3">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>-0.087033398821219,2.782318271119842 2.314145383104125,2.757563850687622 2.611198428290766,4.688408644400785 2.611198428290766,2.807072691552063 5.284675834970531,2.782318271119842 7.388801571709235,4.713163064833005 9.789980353634579,2.757563850687622 10.631630648330061,2.757563850687622</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:simplify_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:simplify_lines fid="2">
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>0.061493123772101,-0.237721021611003 1.967583497053045,-0.262475442043224 4.34400785854617,2.262475442043221 6.448133595284873,-0.262475442043224 10.606876227897841,-0.188212180746563</gml:coordinates></gml:LineString></ogr:geometryProperty>
+    </ogr:simplify_lines>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:simplify_lines fid="4">
+    </ogr:simplify_lines>
+  </gml:featureMember>
+</ogr:FeatureCollection>