QGIS/python/plugins/processing/algs/qgis/ConcaveHull.py

# -*- coding: utf-8 -*-

"""
***************************************************************************
    ConcaveHull.py
    ---------------------
    Date                 : May 2014
    Copyright            : (C) 2012 by Piotr Pociask
    Email                : piotr dot pociask at gis-support dot pl
***************************************************************************
*                                                                         *
*   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__ = 'Piotr Pociask'
__date__ = 'May 2014'
__copyright__ = '(C) 2014, Piotr Pociask'

from qgis.PyQt.QtCore import QCoreApplication
from math import sqrt

from qgis.core import (QgsApplication,
                       QgsFeature,
                       QgsFeatureSink,
                       QgsWkbTypes,
                       QgsProcessing,
                       QgsProcessingException,
                       QgsProcessingParameterFeatureSource,
                       QgsProcessingParameterNumber,
                       QgsProcessingParameterBoolean,
                       QgsProcessingParameterFeatureSink)
import processing
from processing.algs.qgis.QgisAlgorithm import QgisAlgorithm


class ConcaveHull(QgisAlgorithm):

    INPUT = 'INPUT'
    ALPHA = 'ALPHA'
    HOLES = 'HOLES'
    NO_MULTIGEOMETRY = 'NO_MULTIGEOMETRY'
    OUTPUT = 'OUTPUT'

    def group(self):
        return self.tr('Vector geometry')

    def groupId(self):
        return 'vectorgeometry'

    def __init__(self):
        super().__init__()

    def initAlgorithm(self, config=None):
        self.addParameter(QgsProcessingParameterFeatureSource(self.INPUT, self.tr('Input point layer'), [QgsProcessing.TypeVectorPoint]))
        self.addParameter(QgsProcessingParameterNumber(self.ALPHA,
                                                       self.tr('Threshold (0-1, where 1 is equivalent with Convex Hull)'),
                                                       minValue=0, maxValue=1, defaultValue=0.3, type=QgsProcessingParameterNumber.Double))

        self.addParameter(QgsProcessingParameterBoolean(self.HOLES,
                                                        self.tr('Allow holes'), defaultValue=True))
        self.addParameter(QgsProcessingParameterBoolean(self.NO_MULTIGEOMETRY,
                                                        self.tr('Split multipart geometry into singleparts geometries'), defaultValue=False))

        self.addParameter(QgsProcessingParameterFeatureSink(self.OUTPUT, self.tr('Concave hull'), type=QgsProcessing.TypeVectorPolygon))

    def name(self):
        return 'concavehull'

    def displayName(self):
        return self.tr('Concave hull (alpha shapes)')

    def shortDescription(self):
        return self.tr('Creates a concave hull using the alpha shapes algorithm.')

    def icon(self):
        return QgsApplication.getThemeIcon("/algorithms/mAlgorithmConcaveHull.svg")

    def svgIconPath(self):
        return QgsApplication.iconPath("/algorithms/mAlgorithmConcaveHull.svg")

    def processAlgorithm(self, parameters, context, feedback):
        layer = self.parameterAsSource(parameters, ConcaveHull.INPUT, context)
        if layer is None:
            raise QgsProcessingException(self.invalidSourceError(parameters, self.INPUT))

        alpha = self.parameterAsDouble(parameters, self.ALPHA, context)
        holes = self.parameterAsBoolean(parameters, self.HOLES, context)
        no_multigeom = self.parameterAsBoolean(parameters, self.NO_MULTIGEOMETRY, context)

        # Delaunay triangulation from input point layer
        feedback.setProgressText(QCoreApplication.translate('ConcaveHull', 'Creating Delaunay triangles…'))
        delaunay_layer = processing.run("qgis:delaunaytriangulation", {'INPUT': parameters[ConcaveHull.INPUT], 'OUTPUT': 'memory:'}, feedback=feedback, context=context)['OUTPUT']

        # Get max edge length from Delaunay triangles
        feedback.setProgressText(QCoreApplication.translate('ConcaveHull', 'Computing edges max length…'))

        features = delaunay_layer.getFeatures()
        count = delaunay_layer.featureCount()
        if count == 0:
            raise QgsProcessingException(self.tr('No Delaunay triangles created.'))

        counter = 50. / count
        lengths = []
        edges = {}
        for feat in features:
            if feedback.isCanceled():
                break

            line = feat.geometry().asPolygon()[0]
            for i in range(len(line) - 1):
                lengths.append(sqrt(line[i].sqrDist(line[i + 1])))
            edges[feat.id()] = max(lengths[-3:])
            feedback.setProgress(feat.id() * counter)
        max_length = max(lengths)

        # Get features with longest edge longer than alpha*max_length
        feedback.setProgressText(QCoreApplication.translate('ConcaveHull', 'Removing features…'))
        counter = 50. / len(edges)
        i = 0
        ids = []
        for id, max_len in edges.items():
            if feedback.isCanceled():
                break

            if max_len > alpha * max_length:
                ids.append(id)
            feedback.setProgress(50 + i * counter)
            i += 1

        # Remove features
        delaunay_layer.dataProvider().deleteFeatures(ids)

        # Dissolve all Delaunay triangles
        feedback.setProgressText(QCoreApplication.translate('ConcaveHull', 'Dissolving Delaunay triangles…'))
        dissolved_layer = processing.run("native:dissolve", {'INPUT': delaunay_layer, 'OUTPUT': 'memory:'}, feedback=feedback, context=context)['OUTPUT']

        # Save result
        feedback.setProgressText(QCoreApplication.translate('ConcaveHull', 'Saving data…'))
        feat = QgsFeature()
        dissolved_layer.getFeatures().nextFeature(feat)

        # Not needed anymore, free up some resources
        del delaunay_layer
        del dissolved_layer

        (sink, dest_id) = self.parameterAsSink(parameters, self.OUTPUT, context,
                                               layer.fields(), QgsWkbTypes.Polygon, layer.sourceCrs())
        if sink is None:
            raise QgsProcessingException(self.invalidSinkError(parameters, self.OUTPUT))

        geom = feat.geometry()
        if no_multigeom and geom.isMultipart():
            # Only singlepart geometries are allowed
            geom_list = geom.asGeometryCollection()
            for single_geom in geom_list:
                if feedback.isCanceled():
                    break

                single_feature = QgsFeature()
                if not holes:
                    # Delete holes
                    single_geom = single_geom.removeInteriorRings()
                single_feature.setGeometry(single_geom)
                sink.addFeature(single_feature, QgsFeatureSink.FastInsert)
        else:
            # Multipart geometries are allowed
            if not holes:
                # Delete holes
                geom = geom.removeInteriorRings()
                feat.setGeometry(geom)
            sink.addFeature(feat, QgsFeatureSink.FastInsert)

        return {self.OUTPUT: dest_id}