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Implements a method in QgsGeometry and a processing algorithm to calculate the pole of inaccessibility for a surface, which is the most distant internal point from the boundary of the surface. This function uses the 'polylabel' algorithm (Vladimir Agafonkin, 2016), which is an iterative approach guaranteed to find the true pole of inaccessibility within a specified tolerance. More precise tolerances require more iterations and will take longer to calculate.
87 lines
3.2 KiB
Python
87 lines
3.2 KiB
Python
# -*- coding: utf-8 -*-
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"""
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***************************************************************************
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PointOnSurface.py
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--------------
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Date : July 2016
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Copyright : (C) 2016 by Nyall Dawson
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Email : nyall dot dawson at gmail dot com
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***************************************************************************
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* *
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* This program is free software; you can redistribute it and/or modify *
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* it under the terms of the GNU General Public License as published by *
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* the Free Software Foundation; either version 2 of the License, or *
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* (at your option) any later version. *
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* *
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***************************************************************************
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"""
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__author__ = 'Nyall Dawson'
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__date__ = 'July 2016'
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__copyright__ = '(C) 2016, Nyall Dawson'
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# This will get replaced with a git SHA1 when you do a git archive323
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__revision__ = '$Format:%H$'
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import os
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from qgis.core import QgsGeometry, QgsWkbTypes
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from qgis.PyQt.QtGui import QIcon
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from processing.core.GeoAlgorithm import GeoAlgorithm
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from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
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from processing.core.parameters import ParameterVector
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from processing.core.outputs import OutputVector
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from processing.tools import dataobjects, vector
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pluginPath = os.path.split(os.path.split(os.path.dirname(__file__))[0])[0]
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class PointOnSurface(GeoAlgorithm):
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INPUT_LAYER = 'INPUT_LAYER'
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OUTPUT_LAYER = 'OUTPUT_LAYER'
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def getIcon(self):
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return QIcon(os.path.join(pluginPath, 'images', 'ftools', 'centroids.png'))
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def defineCharacteristics(self):
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self.name, self.i18n_name = self.trAlgorithm('Point on surface')
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self.group, self.i18n_group = self.trAlgorithm('Vector geometry tools')
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self.addParameter(ParameterVector(self.INPUT_LAYER,
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self.tr('Input layer')))
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self.addOutput(OutputVector(self.OUTPUT_LAYER, self.tr('Point'), datatype=[dataobjects.TYPE_VECTOR_POINT]))
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def processAlgorithm(self, progress):
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layer = dataobjects.getObjectFromUri(
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self.getParameterValue(self.INPUT_LAYER))
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writer = self.getOutputFromName(
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self.OUTPUT_LAYER).getVectorWriter(
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layer.fields().toList(),
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QgsWkbTypes.Point,
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layer.crs())
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features = vector.features(layer)
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total = 100.0 / len(features)
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for current, input_feature in enumerate(features):
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output_feature = input_feature
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input_geometry = input_feature.geometry()
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if input_geometry:
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output_geometry = input_geometry.pointOnSurface()
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if not output_geometry:
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raise GeoAlgorithmExecutionException(
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self.tr('Error calculating point on surface'))
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output_feature.setGeometry(output_geometry)
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writer.addFeature(output_feature)
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progress.setPercentage(int(current * total))
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del writer
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