[FEATURE] New processing algorithm "minimum bounding geometry"

This algorithm creates geometries which enclose the features
from an input layer.

Numerous enclosing geometry types are supported, including
bounding boxes (envelopes), oriented rectangles, circles and
convex hulls.

Optionally, the features can be grouped by a field. If set,
this causes the output layer to contain one feature per grouped
value with a minimal geometry covering just the features with
matching values.

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

@@ -324,6 +324,13 @@ qgis:mergevectorlayers: >
 
   The layers will all be reprojected to match the coordinate reference system of the first input layer.
 
+qgis:minimumboundinggeometry: >
+  This algorithm creates geometries which enclose the features from an input layer.
+
+  Numerous enclosing geometry types are supported, including bounding boxes (envelopes), oriented rectangles, circles and convex hulls.
+
+  Optionally, the features can be grouped by a field. If set, this causes the output layer to contain one feature per grouped value with a minimal geometry covering just the features with matching values.
+
 qgis:multiparttosingleparts: >
   This algorithm takes a vector layer with multipart geometries and generates a new one in which all geometries contain a single part. Features with multipart geometries are divided in as many different features as parts the geometry contain, and the same attributes are used for each of them.
 

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

@@ -0,0 +1,237 @@
+# -*- coding: utf-8 -*-
+
+"""
+***************************************************************************
+    MinimumBoundingGeometry.py
+    --------------------------
+    Date                 : September 2017
+    Copyright            : (C) 2017 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.                                   *
+*                                                                         *
+***************************************************************************
+"""
+from builtins import str
+
+__author__ = 'Nyall Dawson'
+__date__ = 'September 2017'
+__copyright__ = '(C) 2017, 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.QtGui import QIcon
+from qgis.PyQt.QtCore import QVariant
+
+from qgis.core import (QgsField,
+                       QgsFeatureSink,
+                       QgsGeometry,
+                       QgsWkbTypes,
+                       QgsFeatureRequest,
+                       QgsFields,
+                       QgsProcessingParameterFeatureSource,
+                       QgsProcessingParameterField,
+                       QgsProcessingParameterEnum,
+                       QgsProcessingParameterFeatureSink,
+                       QgsProcessing,
+                       QgsFeature,
+                       QgsVertexId,
+                       QgsMultiPointV2)
+
+from processing.algs.qgis.QgisAlgorithm import QgisAlgorithm
+
+pluginPath = os.path.split(os.path.split(os.path.dirname(__file__))[0])[0]
+
+
+class MinimumBoundingGeometry(QgisAlgorithm):
+
+    INPUT = 'INPUT'
+    OUTPUT = 'OUTPUT'
+    TYPE = 'TYPE'
+    FIELD = 'FIELD'
+
+    def icon(self):
+        return QIcon(os.path.join(pluginPath, 'images', 'ftools', 'convex_hull.png'))
+
+    def group(self):
+        return self.tr('Vector geometry')
+
+    def __init__(self):
+        super().__init__()
+        self.type_names = [self.tr('Envelope (Bounding Box)'),
+                           self.tr('Minimum Oriented Rectangle'),
+                           self.tr('Minimum Enclosing Circle'),
+                           self.tr('Convex Hull')]
+
+    def initAlgorithm(self, config=None):
+        self.addParameter(QgsProcessingParameterFeatureSource(self.INPUT,
+                                                              self.tr('Input layer')))
+        self.addParameter(QgsProcessingParameterField(self.FIELD,
+                                                      self.tr('Field (optional, set if features should be grouped by class)'),
+                                                      parentLayerParameterName=self.INPUT, optional=True))
+        self.addParameter(QgsProcessingParameterEnum(self.TYPE,
+                                                     self.tr('Geometry type'), options=self.type_names))
+        self.addParameter(QgsProcessingParameterFeatureSink(self.OUTPUT, self.tr('Bounding geometry'), QgsProcessing.TypeVectorPolygon))
+
+    def name(self):
+        return 'minimumboundinggeometry'
+
+    def displayName(self):
+        return self.tr('Minimum bounding geometry')
+
+    def tags(self):
+        return self.tr('bounding,box,bounds,envelope,minimum,oriented,rectangle,enclosing,circle,convex,hull,generalization').split(',')
+
+    def processAlgorithm(self, parameters, context, feedback):
+        source = self.parameterAsSource(parameters, self.INPUT, context)
+        field_name = self.parameterAsString(parameters, self.FIELD, context)
+        type = self.parameterAsEnum(parameters, self.TYPE, context)
+        use_field = bool(field_name)
+
+        field_index = -1
+
+        fields = QgsFields()
+        fields.append(QgsField('id', QVariant.Int, '', 20))
+
+        if use_field:
+            # keep original field type, name and parameters
+            field_index = source.fields().lookupField(field_name)
+            if field_index >= 0:
+                fields.append(source.fields()[field_index])
+        if type == 0:
+            #envelope
+            fields.append(QgsField('width', QVariant.Double, '', 20, 6))
+            fields.append(QgsField('height', QVariant.Double, '', 20, 6))
+            fields.append(QgsField('area', QVariant.Double, '', 20, 6))
+            fields.append(QgsField('perimeter', QVariant.Double, '', 20, 6))
+        elif type == 1:
+            #oriented rect
+            fields.append(QgsField('width', QVariant.Double, '', 20, 6))
+            fields.append(QgsField('height', QVariant.Double, '', 20, 6))
+            fields.append(QgsField('angle', QVariant.Double, '', 20, 6))
+            fields.append(QgsField('area', QVariant.Double, '', 20, 6))
+            fields.append(QgsField('perimeter', QVariant.Double, '', 20, 6))
+        elif type == 2:
+            # circle
+            fields.append(QgsField('radius', QVariant.Double, '', 20, 6))
+            fields.append(QgsField('area', QVariant.Double, '', 20, 6))
+        elif type == 3:
+            # convex hull
+            fields.append(QgsField('area', QVariant.Double, '', 20, 6))
+            fields.append(QgsField('perimeter', QVariant.Double, '', 20, 6))
+
+        (sink, dest_id) = self.parameterAsSink(parameters, self.OUTPUT, context,
+                                               fields, QgsWkbTypes.Polygon, source.sourceCrs())
+
+        if field_index >= 0:
+            geometry_dict = {}
+            total = 50.0 / source.featureCount() if source.featureCount() else 1
+            features = source.getFeatures(QgsFeatureRequest().setSubsetOfAttributes([field_index]))
+            for current, f in enumerate(features):
+                if feedback.isCanceled():
+                    break
+
+                if not f.hasGeometry():
+                    continue
+
+                if not f.attributes()[field_index] in geometry_dict:
+                    geometry_dict[f.attributes()[field_index]] = [f.geometry()]
+                else:
+                    geometry_dict[f.attributes()[field_index]].append(f.geometry())
+
+                feedback.setProgress(int(current * total))
+
+            current = 0
+            total = 50.0 / len(geometry_dict) if geometry_dict else 1
+            for group, geometries in geometry_dict.items():
+                if feedback.isCanceled():
+                    break
+
+                feature = self.createFeature(feedback, current, type, geometries, group)
+                sink.addFeature(feature, QgsFeatureSink.FastInsert)
+                geometry_dict[group] = None
+
+                feedback.setProgress(50 + int(current * total))
+                current += 1
+        else:
+            total = 80.0 / source.featureCount() if source.featureCount() else 1
+            features = source.getFeatures(QgsFeatureRequest().setSubsetOfAttributes([]))
+            geometry_queue = []
+            for current, f in enumerate(features):
+                if feedback.isCanceled():
+                    break
+
+                if not f.hasGeometry():
+                    continue
+
+                geometry_queue.append(f.geometry())
+                feedback.setProgress(int(current * total))
+
+            if not feedback.isCanceled():
+                feature = self.createFeature(feedback, 0, type, geometry_queue)
+                sink.addFeature(feature, QgsFeatureSink.FastInsert)
+
+        return {self.OUTPUT: dest_id}
+
+    def createFeature(self, feedback, feature_id, type, geometries, class_field=None):
+        attrs = [feature_id]
+        if class_field is not None:
+            attrs.append(class_field)
+
+        multi_point = QgsMultiPointV2()
+
+        for g in geometries:
+            if feedback.isCanceled():
+                break
+
+            vid = QgsVertexId()
+            while True:
+                if feedback.isCanceled():
+                    break
+                found, point = g.geometry().nextVertex(vid)
+                if found:
+                    multi_point.addGeometry(point)
+                else:
+                    break
+
+        geometry = QgsGeometry(multi_point)
+        output_geometry = None
+        if type == 0:
+            # envelope
+            rect = geometry.boundingBox()
+            output_geometry = QgsGeometry.fromRect(rect)
+            attrs.append(rect.width())
+            attrs.append(rect.height())
+            attrs.append(rect.area())
+            attrs.append(rect.perimeter())
+        elif type == 1:
+            # oriented rect
+            output_geometry, area, angle, width, height = geometry.orientedMinimumBoundingBox()
+            attrs.append(width)
+            attrs.append(height)
+            attrs.append(angle)
+            attrs.append(area)
+            attrs.append(2 * width + 2 * height)
+        elif type == 2:
+            # circle
+            output_geometry, center, radius = geometry.minimalEnclosingCircle(segments=72)
+            attrs.append(radius)
+            attrs.append(math.pi * radius * radius)
+        elif type == 3:
+            # convex hull
+            output_geometry = geometry.convexHull()
+            attrs.append(output_geometry.geometry().area())
+            attrs.append(output_geometry.geometry().perimeter())
+        f = QgsFeature()
+        f.setAttributes(attrs)
+        f.setGeometry(output_geometry)
+        return f

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

@@ -100,6 +100,7 @@
 from .MeanCoords import MeanCoords
 from .Merge import Merge
 from .MergeLines import MergeLines
+from .MinimumBoundingGeometry import MinimumBoundingGeometry
 from .MinimalEnclosingCircle import MinimalEnclosingCircle
 from .NearestNeighbourAnalysis import NearestNeighbourAnalysis
 from .OffsetLine import OffsetLine
@@ -254,6 +255,7 @@ def getAlgs(self):
                 MeanCoords(),
                 Merge(),
                 MergeLines(),
+                MinimumBoundingGeometry(),
                 MinimalEnclosingCircle(),
                 NearestNeighbourAnalysis(),
                 OffsetLine(),

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

@@ -0,0 +1,37 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>mbg_circle_field</Name>
+    <ElementPath>mbg_circle_field</ElementPath>
+    <!--POLYGON-->
+    <GeometryType>3</GeometryType>
+    <SRSName>EPSG:4326</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>4</FeatureCount>
+      <ExtentXMin>-2.10952</ExtentXMin>
+      <ExtentXMax>9.37006</ExtentXMax>
+      <ExtentYMin>-4.60952</ExtentYMin>
+      <ExtentYMax>7.10328</ExtentYMax>
+    </DatasetSpecificInfo>
+    <PropertyDefn>
+      <Name>id</Name>
+      <ElementPath>id</ElementPath>
+      <Type>Integer</Type>
+    </PropertyDefn>
+    <PropertyDefn>
+      <Name>name</Name>
+      <ElementPath>name</ElementPath>
+      <Type>String</Type>
+      <Width>2</Width>
+    </PropertyDefn>
+    <PropertyDefn>
+      <Name>radius</Name>
+      <ElementPath>radius</ElementPath>
+      <Type>Real</Type>
+    </PropertyDefn>
+    <PropertyDefn>
+      <Name>area</Name>
+      <ElementPath>area</ElementPath>
+      <Type>Real</Type>
+    </PropertyDefn>
+  </GMLFeatureClass>
+</GMLFeatureClassList>