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[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.
1 parent fbd6618 commit 56b77db

9 files changed

+193
-2
lines changed

‎python/plugins/processing/algs/help/qgis.yaml

+2
Original file line numberDiff line numberDiff line change
@@ -429,6 +429,8 @@ qgis:setstyleforvectorlayer: >
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qgis:simplifygeometries: >
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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.
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The algorithm gives a choice of simplification methods, including distance based (the "Douglas-Peucker" algorithm), area based ("Visvalingam" algorithm) and snapping geometries to grid.
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qgis:singlepartstomultipart:
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‎python/plugins/processing/algs/qgis/SimplifyGeometries.py

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

‎python/plugins/processing/tests/testdata/expected/simplify_grid_lines.gfs

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@@ -0,0 +1,15 @@
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<GMLFeatureClassList>
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<GMLFeatureClass>
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<Name>simplify_grid_lines</Name>
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<ElementPath>simplify_grid_lines</ElementPath>
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<GeometryType>2</GeometryType>
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<SRSName>EPSG:4326</SRSName>
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<DatasetSpecificInfo>
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<FeatureCount>4</FeatureCount>
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<ExtentXMin>-0.08703</ExtentXMin>
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<ExtentXMax>10.63163</ExtentXMax>
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<ExtentYMin>-0.26248</ExtentYMin>
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<ExtentYMax>4.98546</ExtentYMax>
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</DatasetSpecificInfo>
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</GMLFeatureClass>
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</GMLFeatureClassList>

‎python/plugins/processing/tests/testdata/expected/simplify_grid_lines.gml

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<?xml version="1.0" encoding="utf-8" ?>
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<ogr:FeatureCollection
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation=""
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xmlns:ogr="http://ogr.maptools.org/"
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xmlns:gml="http://www.opengis.net/gml">
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<gml:boundedBy>
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<gml:Box>
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<gml:coord><gml:X>-0.08703339882121899</gml:X><gml:Y>-0.262475442043224</gml:Y></gml:coord>
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<gml:coord><gml:X>10.63163064833006</gml:X><gml:Y>4.985461689587426</gml:Y></gml:coord>
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</gml:Box>
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</gml:boundedBy>
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<gml:featureMember>
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<ogr:simplify_grid_lines fid="1">
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<ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>-0.062278978388999,4.985461689587426 5.606483300589391,4.985461689587426</gml:coordinates></gml:LineString></ogr:geometryProperty>
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</ogr:simplify_grid_lines>
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</gml:featureMember>
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<gml:featureMember>
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<ogr:simplify_grid_lines fid="3">
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<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>
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</ogr:simplify_grid_lines>
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</gml:featureMember>
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<gml:featureMember>
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<ogr:simplify_grid_lines fid="2">
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<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>
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</ogr:simplify_grid_lines>
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</gml:featureMember>
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<gml:featureMember>
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<ogr:simplify_grid_lines fid="4">
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</ogr:simplify_grid_lines>
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</gml:featureMember>
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</ogr:FeatureCollection>

‎python/plugins/processing/tests/testdata/expected/simplify_vis_lines.gfs

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@@ -0,0 +1,15 @@
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<GMLFeatureClassList>
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<GMLFeatureClass>
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<Name>simplify_vis_lines</Name>
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<ElementPath>simplify_vis_lines</ElementPath>
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<GeometryType>2</GeometryType>
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<SRSName>EPSG:4326</SRSName>
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<DatasetSpecificInfo>
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<FeatureCount>4</FeatureCount>
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<ExtentXMin>-0.08703</ExtentXMin>
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<ExtentXMax>10.63163</ExtentXMax>
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<ExtentYMin>-0.26248</ExtentYMin>
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<ExtentYMax>4.98546</ExtentYMax>
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</DatasetSpecificInfo>
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</GMLFeatureClass>
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</GMLFeatureClassList>

‎python/plugins/processing/tests/testdata/expected/simplify_vis_lines.gml

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<?xml version="1.0" encoding="utf-8" ?>
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<ogr:FeatureCollection
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation=""
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xmlns:ogr="http://ogr.maptools.org/"
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xmlns:gml="http://www.opengis.net/gml">
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<gml:boundedBy>
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<gml:Box>
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<gml:coord><gml:X>-0.08703339882121899</gml:X><gml:Y>-0.262475442043224</gml:Y></gml:coord>
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<gml:coord><gml:X>10.63163064833006</gml:X><gml:Y>4.985461689587426</gml:Y></gml:coord>
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</gml:Box>
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</gml:boundedBy>
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<gml:featureMember>
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<ogr:simplify_vis_lines fid="1">
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<ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>-0.062278978388999,4.985461689587426 5.606483300589391,4.985461689587426</gml:coordinates></gml:LineString></ogr:geometryProperty>
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</ogr:simplify_vis_lines>
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</gml:featureMember>
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<gml:featureMember>
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<ogr:simplify_vis_lines fid="3">
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<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>
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</ogr:simplify_vis_lines>
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</gml:featureMember>
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<gml:featureMember>
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<ogr:simplify_vis_lines fid="2">
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<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>
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</ogr:simplify_vis_lines>
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</gml:featureMember>
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<gml:featureMember>
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<ogr:simplify_vis_lines fid="4">
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</ogr:simplify_vis_lines>
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</gml:featureMember>
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</ogr:FeatureCollection>

‎python/plugins/processing/tests/testdata/qgis_algorithm_tests.yaml

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@@ -939,3 +939,29 @@ tests:
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OUTPUT:
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name: expected/simplify_multilines.gml
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type: vector
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- algorithm: qgis:simplifygeometries
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name: Simplify (visval)
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params:
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INPUT:
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name: simplify_lines.gml
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type: vector
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METHOD: '2'
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TOLERANCE: 1.0
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results:
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OUTPUT:
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name: expected/simplify_vis_lines.gml
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type: vector
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- algorithm: qgis:simplifygeometries
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name: Simplify (grid)
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params:
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INPUT:
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name: simplify_lines.gml
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type: vector
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METHOD: '1'
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TOLERANCE: 5.0
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results:
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OUTPUT:
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name: expected/simplify_grid_lines.gml
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type: vector

‎python/plugins/processing/tests/testdata/simplify_lines.gfs

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<GMLFeatureClassList>
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<GMLFeatureClass>
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<Name>simplify_lines</Name>
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<ElementPath>simplify_lines</ElementPath>
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<GeometryType>2</GeometryType>
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<SRSName>EPSG:4326</SRSName>
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<DatasetSpecificInfo>
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<FeatureCount>4</FeatureCount>
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<ExtentXMin>-0.08703</ExtentXMin>
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<ExtentXMax>10.63163</ExtentXMax>
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<ExtentYMin>-0.26248</ExtentYMin>
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<ExtentYMax>4.98546</ExtentYMax>
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</DatasetSpecificInfo>
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</GMLFeatureClass>
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</GMLFeatureClassList>

‎python/plugins/processing/tests/testdata/simplify_lines.gml

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<?xml version="1.0" encoding="utf-8" ?>
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<ogr:FeatureCollection
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation=""
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xmlns:ogr="http://ogr.maptools.org/"
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xmlns:gml="http://www.opengis.net/gml">
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<gml:boundedBy>
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<gml:Box>
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<gml:coord><gml:X>-0.08703339882121885</gml:X><gml:Y>-0.2624754420432236</gml:Y></gml:coord>
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<gml:coord><gml:X>10.63163064833006</gml:X><gml:Y>4.985461689587426</gml:Y></gml:coord>
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</gml:Box>
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</gml:boundedBy>
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<gml:featureMember>
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<ogr:simplify_lines fid="1">
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<ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>-0.062278978388999,4.985461689587426 5.606483300589391,4.985461689587426</gml:coordinates></gml:LineString></ogr:geometryProperty>
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</ogr:simplify_lines>
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</gml:featureMember>
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<gml:featureMember>
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<ogr:simplify_lines fid="3">
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<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>
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</ogr:simplify_lines>
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</gml:featureMember>
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<gml:featureMember>
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<ogr:simplify_lines fid="2">
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<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>
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</ogr:simplify_lines>
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</gml:featureMember>
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<gml:featureMember>
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<ogr:simplify_lines fid="4">
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</ogr:simplify_lines>
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</gml:featureMember>
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</ogr:FeatureCollection>

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