[processing] new tool: random point in given extent

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

@@ -90,6 +90,7 @@
 from ZonalStatistics import ZonalStatistics
 from PointsFromPolygons import PointsFromPolygons
 from PointsFromLines import PointsFromLines
+from RandomPointsExtent import RandomPointsExtent
 
 # from VectorLayerHistogram import VectorLayerHistogram
 # from VectorLayerScatterplot import VectorLayerScatterplot
@@ -119,8 +120,9 @@ def __init__(self):
                         VariableDistanceBuffer(), Dissolve(), Difference(),
                         Intersection(), Union(), Clip(), ExtentFromLayer(),
                         RandomSelection(), RandomSelectionWithinSubsets(),
-                        SelectByLocation(), RandomExtract(), RandomExtractWithinSubsets(),
-                        ExtractByLocation(), SpatialJoin(),
+                        SelectByLocation(), RandomExtract(),
+                        RandomExtractWithinSubsets(), ExtractByLocation(),
+                        SpatialJoin(),
                         # ------ mmqgisx ------
                         mmqgisx_delete_columns_algorithm(),
                         mmqgisx_delete_duplicate_geometries_algorithm(),
@@ -141,7 +143,7 @@ def __init__(self):
                         StatisticsByCategories(), ConcaveHull(), Polygonize(),
                         RasterLayerStatistics(), PointsDisplacement(),
                         ZonalStatistics(), PointsFromPolygons(),
-                        PointsFromLines(),
+                        PointsFromLines(), RandomPointsExtent(),
                         # ------ raster ------
                         # CreateConstantRaster(),
                         # ------ graphics ------

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

@@ -0,0 +1,127 @@
+# -*- coding: utf-8 -*-
+
+"""
+***************************************************************************
+    RandomPointsExtent.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.ParameterExtent import ParameterExtent
+from processing.parameters.ParameterNumber import ParameterNumber
+from processing.outputs.OutputVector import OutputVector
+
+
+class RandomPointsExtent(GeoAlgorithm):
+
+    EXTENT = 'EXTENT'
+    POINT_NUMBER = 'POINT_NUMBER'
+    MIN_DISTANCE = 'MIN_DISTANCE'
+    OUTPUT = 'OUTPUT'
+
+    def defineCharacteristics(self):
+        self.name = 'Random points in extent'
+        self.group = 'Vector creation tools'
+        self.addParameter(ParameterExtent(self.EXTENT, 'Input extent'))
+        self.addParameter(
+            ParameterNumber(self.POINT_NUMBER, 'Points number', 1, 9999999, 1))
+        self.addParameter(ParameterNumber(
+            self.MIN_DISTANCE, 'Minimum distance', 0.0, 9999999, 0.0))
+        self.addOutput(OutputVector(self.OUTPUT, 'Random points'))
+
+    def processAlgorithm(self, progress):
+        pointCount = int(self.getParameterValue(self.POINT_NUMBER))
+        minDistance = float(self.getParameterValue(self.MIN_DISTANCE))
+        extent = str(self.getParameterValue(self.EXTENT)).split(',')
+
+        xMin = float(extent[0])
+        xMax = float(extent[1])
+        yMin = float(extent[2])
+        yMax = float(extent[3])
+        extent = QgsGeometry().fromRect(
+            QgsRectangle(xMin, yMin, xMax, yMax))
+
+        fields = QgsFields()
+        fields.append(QgsField('id', QVariant.Int, '', 10, 0))
+        mapCRS = interface.iface.mapCanvas().mapSettings().destinationCrs()
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
+            fields, QGis.WKBPoint, mapCRS)
+
+        nPoints = 0
+        nIterations = 0
+        maxIterations = pointCount * 200
+        total = 100.0 / pointCount
+
+        index = QgsSpatialIndex()
+        points = dict()
+
+        while nIterations < maxIterations and nPoints < pointCount:
+            rx = xMin + (xMax - xMin) * random.random()
+            ry = yMin + (yMax - yMin) * random.random()
+
+            pnt = QgsPoint(rx, ry)
+            geom = QgsGeometry.fromPoint(pnt)
+            if geom.within(extent) 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.')
+
+        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