[processing] new tool: random points along lines

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

@@ -94,6 +94,7 @@
 from RandomPointsLayer import RandomPointsLayer
 from RandomPointsPolygonsFixed import RandomPointsPolygonsFixed
 from RandomPointsPolygonsVariable import RandomPointsPolygonsVariable
+from RandomPointsAlongLines import RandomPointsAlongLines
 
 # from VectorLayerHistogram import VectorLayerHistogram
 # from VectorLayerScatterplot import VectorLayerScatterplot
@@ -149,6 +150,7 @@ def __init__(self):
                         PointsFromLines(), RandomPointsExtent(),
                         RandomPointsLayer(), RandomPointsPolygonsFixed(),
                         RandomPointsPolygonsVariable(),
+                        RandomPointsAlongLines(),
                         # ------ raster ------
                         # CreateConstantRaster(),
                         # ------ graphics ------

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

@@ -0,0 +1,139 @@
+# -*- coding: utf-8 -*-
+
+"""
+***************************************************************************
+    RandomPointsAlongLines.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 RandomPointsAlongLines(GeoAlgorithm):
+
+    VECTOR = 'VECTOR'
+    POINT_NUMBER = 'POINT_NUMBER'
+    MIN_DISTANCE = 'MIN_DISTANCE'
+    OUTPUT = 'OUTPUT'
+
+    def defineCharacteristics(self):
+        self.name = 'Random points along line'
+        self.group = 'Vector creation tools'
+        self.addParameter(ParameterVector(self.VECTOR,
+            'Input layer',[ParameterVector.VECTOR_TYPE_LINE]))
+        self.addParameter(ParameterNumber
+            (self.POINT_NUMBER, 'Number of points', 1, 9999999, 1))
+        self.addParameter(ParameterNumber(
+            self.MIN_DISTANCE, 'Minimum distance', 0.0, 9999999.0, 0.0))
+        self.addOutput(OutputVector(self.OUTPUT, 'Random points'))
+
+    def processAlgorithm(self, progress):
+        layer = dataobjects.getObjectFromUri(
+            self.getParameterValue(self.VECTOR))
+        pointCount = float(self.getParameterValue(self.POINT_NUMBER))
+        minDistance = float(self.getParameterValue(self.MIN_DISTANCE))
+
+        fields = QgsFields()
+        fields.append(QgsField('id', QVariant.Int, '', 10, 0))
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
+            fields, QGis.WKBPoint, layer.dataProvider().crs())
+
+        nPoints = 0
+        nIterations = 0
+        maxIterations = pointCount * 200
+        featureCount = layer.featureCount()
+        total = 100.0 / pointCount
+
+        index = QgsSpatialIndex()
+        points = dict()
+
+        da = QgsDistanceArea()
+        request = QgsFeatureRequest()
+
+        random.seed()
+
+        while nIterations < maxIterations and nPoints < pointCount:
+            # pick random feature
+            fid = random.randint(0, featureCount - 1)
+            f = layer.getFeatures(request.setFilterFid(fid)).next()
+            fGeom = QgsGeometry(f.geometry())
+
+            if fGeom.isMultipart():
+                lines = fGeom.asMultiPolyline()
+                # pick random line
+                lineId = random.randint(0, len(lines) - 1)
+                vertices = lines[lineId]
+            else:
+                vertices = fGeom.asPolyline()
+
+            # pick random segment
+            if len(vertices) == 2:
+                vid = 0
+            else:
+                vid = random.randint(0, len(vertices) - 2)
+            startPoint = vertices[vid]
+            endPoint = vertices[vid + 1]
+            length = da.measureLine(startPoint, endPoint)
+            dist = length * random.random()
+
+            if dist > minDistance:
+                d = dist / (length - dist)
+                rx = (startPoint.x() + d * endPoint.x()) / (1 + d)
+                ry = (startPoint.y() + d * endPoint.y()) / (1 + d)
+
+                # generate random point
+                pnt = QgsPoint(rx, ry)
+                geom = QgsGeometry.fromPoint(pnt)
+                if vector.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