[processing] new tool: random points within polygons

Work done for Faunalia funded by Prof. António Mira (University of Évora,
Portugal, Unidade de Biologia da Conservação) and Dr. Rosana Peixoto

Author: alexbruy

python/plugins/processing/algs/qgis/QGISAlgorithmProvider.py

@@ -92,6 +92,7 @@
 from PointsFromLines import PointsFromLines
 from RandomPointsExtent import RandomPointsExtent
 from RandomPointsLayer import RandomPointsLayer
+from RandomPointsPolygonsFixed import RandomPointsPolygonsFixed
 
 # from VectorLayerHistogram import VectorLayerHistogram
 # from VectorLayerScatterplot import VectorLayerScatterplot
@@ -145,7 +146,7 @@ def __init__(self):
                         RasterLayerStatistics(), PointsDisplacement(),
                         ZonalStatistics(), PointsFromPolygons(),
                         PointsFromLines(), RandomPointsExtent(),
-                        RandomPointsLayer(),
+                        RandomPointsLayer(), RandomPointsPolygonsFixed(),
                         # ------ raster ------
                         # CreateConstantRaster(),
                         # ------ graphics ------

python/plugins/processing/algs/qgis/RandomPointsPolygonsFixed.py

@@ -0,0 +1,146 @@
+# -*- coding: utf-8 -*-
+
+"""
+***************************************************************************
+    RandomPointsPolygonsFixed.py
+    ---------------------
+    Date                 : April 2014
+    Copyright            : (C) 2014 by Alexander Bruy
+    Email                : alexander dot bruy 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__ = 'Alexander Bruy'
+__date__ = 'April 2014'
+__copyright__ = '(C) 2014, Alexander Bruy'
+
+# This will get replaced with a git SHA1 when you do a git archive
+
+__revision__ = '$Format:%H$'
+
+import math
+import random
+
+from PyQt4.QtCore import *
+
+from qgis.core import *
+
+from processing import interface
+from processing.core.GeoAlgorithm import GeoAlgorithm
+from processing.core.ProcessingLog import ProcessingLog
+from processing.parameters.ParameterVector import ParameterVector
+from processing.parameters.ParameterNumber import ParameterNumber
+from processing.parameters.ParameterSelection import ParameterSelection
+from processing.outputs.OutputVector import OutputVector
+from processing.tools import dataobjects, vector
+
+
+class RandomPointsPolygonsFixed(GeoAlgorithm):
+
+    VECTOR = 'VECTOR'
+    VALUE = 'VALUE'
+    MIN_DISTANCE = 'MIN_DISTANCE'
+    STRATEGY = 'STRATEGY'
+    OUTPUT = 'OUTPUT'
+
+    STRATEGIES = ['Points count',
+                  'Points density'
+                 ]
+
+    def defineCharacteristics(self):
+        self.name = 'Random points inside polygons'
+        self.group = 'Vector creation tools'
+        self.addParameter(ParameterVector(self.VECTOR,
+            'Input layer',[ParameterVector.VECTOR_TYPE_POLYGON]))
+        self.addParameter(ParameterSelection(
+            self.STRATEGY, 'Sampling strategy', self.STRATEGIES, 0))
+        self.addParameter(
+            ParameterNumber(self.VALUE, 'Number or density of points', 0.0001, 9999999.0, 1.0))
+        self.addParameter(ParameterNumber(
+            self.MIN_DISTANCE, 'Minimum distance', 0.0, 9999999, 0.0))
+        self.addOutput(OutputVector(self.OUTPUT, 'Random points'))
+
+    def processAlgorithm(self, progress):
+        layer = dataobjects.getObjectFromUri(
+            self.getParameterValue(self.VECTOR))
+        value = float(self.getParameterValue(self.VALUE))
+        minDistance = float(self.getParameterValue(self.MIN_DISTANCE))
+        strategy = self.getParameterValue(self.STRATEGY)
+
+        fields = QgsFields()
+        fields.append(QgsField('id', QVariant.Int, '', 10, 0))
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
+            fields, QGis.WKBPoint, layer.dataProvider().crs())
+
+
+        request = QgsFeatureRequest()
+
+        da = QgsDistanceArea()
+        features = vector.features(layer)
+        for current, f in enumerate(features):
+            fGeom = QgsGeometry(f.geometry())
+            bbox = fGeom.boundingBox()
+            if strategy == 0:
+                pointCount = int(value)
+            else:
+                pointCount = int(round(value * da.measure(fGeom)))
+
+            index = QgsSpatialIndex()
+            points = dict()
+
+            nPoints = 0
+            nIterations = 0
+            maxIterations = pointCount * 200
+            total = 100.0 / pointCount
+
+            while nIterations < maxIterations and nPoints < pointCount:
+                rx = bbox.xMinimum() + bbox.width() * random.random()
+                ry = bbox.yMinimum() + bbox.height() * random.random()
+
+                pnt = QgsPoint(rx, ry)
+                geom = QgsGeometry.fromPoint(pnt)
+                if geom.within(fGeom) and \
+                        self.checkMinDistance(pnt, index, minDistance, points):
+                    f = QgsFeature(nPoints)
+                    f.initAttributes(1)
+                    f.setFields(fields)
+                    f.setAttribute('id', nPoints)
+                    f.setGeometry(geom)
+                    writer.addFeature(f)
+                    index.insertFeature(f)
+                    points[nPoints] = pnt
+                    nPoints += 1
+                    progress.setPercentage(int(nPoints * total))
+                nIterations += 1
+
+            if nPoints < pointCount:
+                 ProcessingLog.addToLog(
+                     ProcessingLog.LOG_INFO,
+                     'Can not generate requested number of random points. Maximum '
+                     'number of attempts exceeded.')
+
+            progress.setPercentage(0)
+
+        del writer
+
+    def checkMinDistance(self, point, index, distance, points):
+        if distance == 0:
+            return True
+
+        neighbors = index.nearestNeighbor(point, 1)
+        if len(neighbors) == 0:
+            return True
+
+        if neighbors[0] in points:
+            np = points[neighbors[0]]
+            if np.sqrDist(point) < (distance * distance):
+                return False
+
+        return True