Merge pull request #3435 from nyalldawson/interpolate_angle

Expression functions to Interpolate angle (+ related processing improvements)

Author: nyalldawson

python/core/geometry/qgsgeometry.sip

@@ -194,6 +194,15 @@ class QgsGeometry
      */
     double distanceToVertex( int vertex ) const;
 
+    /**
+     * Returns the bisector angle for this geometry at the specified vertex.
+     * @param vertex vertex index to calculate bisector angle at
+     * @returns bisector angle, in radians clockwise from north
+     * @note added in QGIS 3.0
+     * @see interpolateAngle()
+     */
+    double angleAtVertex( int vertex ) const;
+
     /**
      * Returns the indexes of the vertices before and after the given vertex index.
      *
@@ -545,6 +554,16 @@ class QgsGeometry
      */
     double lineLocatePoint( const QgsGeometry& point ) const;
 
+    /** Returns the angle parallel to the linestring or polygon boundary at the specified distance
+     * along the geometry. Angles are in radians, clockwise from north.
+     * If the distance coincides precisely at a node then the average angle from the segment either side
+     * of the node is returned.
+     * @param distance distance along geometry
+     * @note added in QGIS 3.0
+     * @see angleAtVertex()
+     */
+    double interpolateAngle( double distance ) const;
+
     /** Returns a geometry representing the points shared by this geometry and other. */
     QgsGeometry intersection( const QgsGeometry& geometry ) const;
 

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

@@ -166,6 +166,8 @@ qgis:extractbylocation: >
 qgis:extractnodes: >
   This algorithm takes a line or polygon layer and generates a point layer with points representing the nodes in the input lines or polygons. The attributes associated to each point are the same ones associated to the line or polygon that the point belongs to.
 
+  Additional fields are added to the nodes indicating the node index (beginning at 0), distance along original geometry and bisector angle of node for original geometry.
+
 qgis:fieldcalculator: >
   This algorithm computes a new vector layer with the same features of the input layer, but with an additional attribute. The values of this new attribute are computed from each feature using a mathematical formula, based on te properties and attributes of the feature.
 
@@ -284,6 +286,11 @@ qgis:orientedminimumboundingbox: >
 
   As an alternative, the output layer can contain not just a single  rectangle, but one for each input feature, representing the minimum rectangle that covers each of them.
 
+qgis:pointsalonglines: >
+  Creates points at regular intervals along line or polygon geometries. Created points will have new attributes added for the distance along the geometry and the angle of the line at the point.
+
+  An optional start and end offset can be specified, which controls how far from the start and end of the geometry the points should be created.
+
 qgis:pointsdisplacement:
 
 

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

@@ -26,10 +26,12 @@
 __revision__ = '$Format:%H$'
 
 import os
+import math
 
 from qgis.PyQt.QtGui import QIcon
+from qgis.PyQt.QtCore import QVariant
 
-from qgis.core import Qgis, QgsFeature, QgsGeometry, QgsWkbTypes
+from qgis.core import QgsFeature, QgsGeometry, QgsWkbTypes, QgsField
 
 from processing.core.GeoAlgorithm import GeoAlgorithm
 from processing.core.parameters import ParameterVector
@@ -61,25 +63,34 @@ def processAlgorithm(self, progress):
         layer = dataobjects.getObjectFromUri(
             self.getParameterValue(self.INPUT))
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
-            layer.fields().toList(), QgsWkbTypes.Point, layer.crs())
+        fields = layer.fields()
+        fields.append(QgsField('node_index', QVariant.Int))
+        fields.append(QgsField('distance', QVariant.Double))
+        fields.append(QgsField('angle', QVariant.Double))
 
-        outFeat = QgsFeature()
-        inGeom = QgsGeometry()
-        outGeom = QgsGeometry()
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
+            fields, QgsWkbTypes.Point, layer.crs())
 
         features = vector.features(layer)
         total = 100.0 / len(features)
         for current, f in enumerate(features):
-            inGeom = f.geometry()
-            attrs = f.attributes()
-
-            points = vector.extractPoints(inGeom)
-            outFeat.setAttributes(attrs)
-
-            for i in points:
-                outFeat.setGeometry(outGeom.fromPoint(i))
-                writer.addFeature(outFeat)
+            input_geometry = f.geometry()
+            if not input_geometry:
+                writer.addFeature(f)
+            else:
+                points = vector.extractPoints(input_geometry)
+
+                for i, point in enumerate(points):
+                    distance = input_geometry.distanceToVertex(i)
+                    angle = math.degrees(input_geometry.angleAtVertex(i))
+                    attrs = f.attributes()
+                    attrs.append(i)
+                    attrs.append(distance)
+                    attrs.append(angle)
+                    output_feature = QgsFeature()
+                    output_feature.setAttributes(attrs)
+                    output_feature.setGeometry(QgsGeometry.fromPoint(point))
+                    writer.addFeature(output_feature)
 
             progress.setPercentage(int(current * total))
 

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

@@ -0,0 +1,113 @@
+# -*- coding: utf-8 -*-
+
+"""
+***************************************************************************
+    PointsAlongGeometry.py
+    ---------------------
+    Date                 : August 2016
+    Copyright            : (C) 2016 by Nyall Dawson
+    Email                : nyall dot dawson 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__ = 'Nyall Dawson'
+__date__ = 'August 2016'
+__copyright__ = '(C) 2016, Nyall Dawson'
+
+# This will get replaced with a git SHA1 when you do a git archive
+
+__revision__ = '$Format:%H$'
+
+import os
+import math
+
+from qgis.PyQt.QtCore import QVariant
+from qgis.PyQt.QtGui import QIcon
+
+from qgis.core import QgsFeature, QgsGeometry, QgsWkbTypes, QgsField
+
+from processing.core.GeoAlgorithm import GeoAlgorithm
+from processing.core.parameters import ParameterVector, ParameterNumber
+from processing.core.outputs import OutputVector
+from processing.tools import dataobjects, vector
+
+pluginPath = os.path.split(os.path.split(os.path.dirname(__file__))[0])[0]
+
+
+class PointsAlongGeometry(GeoAlgorithm):
+
+    INPUT = 'INPUT'
+    OUTPUT = 'OUTPUT'
+    DISTANCE = 'DISTANCE'
+    START_OFFSET = 'START_OFFSET'
+    END_OFFSET = 'END_OFFSET'
+
+    def getIcon(self):
+        return QIcon(os.path.join(pluginPath, 'images', 'ftools', 'extract_nodes.png'))
+
+    def defineCharacteristics(self):
+        self.name, self.i18n_name = self.trAlgorithm('Points along lines')
+        self.group, self.i18n_group = self.trAlgorithm('Vector geometry tools')
+
+        self.addParameter(ParameterVector(self.INPUT,
+                                          self.tr('Input layer'),
+                                          [ParameterVector.VECTOR_TYPE_POLYGON, ParameterVector.VECTOR_TYPE_LINE]))
+        self.addParameter(ParameterNumber(self.DISTANCE,
+                                          self.tr('Distance'), default=1.0))
+        self.addParameter(ParameterNumber(self.START_OFFSET,
+                                          self.tr('Start offset'), default=0.0))
+        self.addParameter(ParameterNumber(self.END_OFFSET,
+                                          self.tr('End offset'), default=0.0))
+        self.addOutput(OutputVector(self.OUTPUT, self.tr('Points')))
+
+    def processAlgorithm(self, progress):
+        layer = dataobjects.getObjectFromUri(
+            self.getParameterValue(self.INPUT))
+        distance = self.getParameterValue(self.DISTANCE)
+        start_offset = self.getParameterValue(self.START_OFFSET)
+        end_offset = self.getParameterValue(self.END_OFFSET)
+
+        fields = layer.fields()
+        fields.append(QgsField('distance', QVariant.Double))
+        fields.append(QgsField('angle', QVariant.Double))
+
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
+            fields, QgsWkbTypes.Point, layer.crs())
+
+        features = vector.features(layer)
+        total = 100.0 / len(features)
+        for current, input_feature in enumerate(features):
+            input_geometry = input_feature.geometry()
+            if not input_geometry:
+                writer.addFeature(input_feature)
+            else:
+                if input_geometry.type == QgsWkbTypes.PolygonGeometry:
+                    length = input_geometry.geometry().perimeter()
+                else:
+                    length = input_geometry.length() - end_offset
+                current_distance = start_offset
+
+                while current_distance <= length:
+                    point = input_geometry.interpolate(current_distance)
+                    angle = math.degrees(input_geometry.interpolateAngle(current_distance))
+
+                    output_feature = QgsFeature()
+                    output_feature.setGeometry(point)
+                    attrs = input_feature.attributes()
+                    attrs.append(current_distance)
+                    attrs.append(angle)
+                    output_feature.setAttributes(attrs)
+                    writer.addFeature(output_feature)
+
+                    current_distance += distance
+
+            progress.setPercentage(int(current * total))
+
+        del writer

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

@@ -154,6 +154,7 @@
 from .PolygonCentroids import PolygonCentroids
 from .Translate import Translate
 from .SingleSidedBuffer import SingleSidedBuffer
+from .PointsAlongGeometry import PointsAlongGeometry
 
 pluginPath = os.path.normpath(os.path.join(
     os.path.split(os.path.dirname(__file__))[0], os.pardir))
@@ -208,7 +209,8 @@ def __init__(self):
                         RectanglesOvalsDiamondsFixed(), MergeLines(),
                         BoundingBox(), Boundary(), PointOnSurface(),
                         OffsetLine(), PolygonCentroids(),
-                        Translate(), SingleSidedBuffer()
+                        Translate(), SingleSidedBuffer(),
+                        PointsAlongGeometry()
                         ]
 
         if hasMatplotlib:

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

@@ -0,0 +1,25 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>extract_nodes_lines</Name>
+    <ElementPath>extract_nodes_lines</ElementPath>
+    <GeometryType>1</GeometryType>
+    <SRSName>EPSG:4326</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>17</FeatureCount>
+      <ExtentXMin>-1.00000</ExtentXMin>
+      <ExtentXMax>11.00000</ExtentXMax>
+      <ExtentYMin>-3.00000</ExtentYMin>
+      <ExtentYMax>5.00000</ExtentYMax>
+    </DatasetSpecificInfo>
+    <PropertyDefn>
+      <Name>distance</Name>
+      <ElementPath>distance</ElementPath>
+      <Type>Real</Type>
+    </PropertyDefn>
+    <PropertyDefn>
+      <Name>angle</Name>
+      <ElementPath>angle</ElementPath>
+      <Type>Real</Type>
+    </PropertyDefn>
+  </GMLFeatureClass>
+</GMLFeatureClassList>