def regularMatrix(self, writer, provider1, provider2, index1, index2, nearest, distArea, sindex, progressBar):
     inFeat = QgsFeature()
     outFeat = QgsFeature()
     inGeom = QgsGeometry()
     outGeom = QgsGeometry()
     first = True
     start = 15.00
     add = 85.00 / provider1.featureCount()
     fit1 = provider1.getFeatures()
     while fit1.nextFeature(inFeat):
         inGeom = inFeat.geometry()
         inID = inFeat.attributes()[index1]
         if first:
             featList = sindex.nearestNeighbor(inGeom.asPoint(), nearest)
             first = False
             data = ["ID"]
             for i in featList:
                 provider2.getFeatures(QgsFeatureRequest().setFilterFid(int(i)).setSubsetOfAttributes([index2])).nextFeature(outFeat)
                 data.append(unicode(outFeat.attributes()[index2]))
             writer.writerow(data)
         data = [unicode(inID)]
         for j in featList:
             provider2.getFeatures(QgsFeatureRequest().setFilterFid(int(j))).nextFeature(outFeat)
             outGeom = outFeat.geometry()
             dist = distArea.measureLine(inGeom.asPoint(), outGeom.asPoint())
             data.append(unicode(float(dist)))
         writer.writerow(data)
         start = start + add
         progressBar.setValue(start)
     del writer

    def setUpClass(cls):
        """Run before all tests"""
        # Register the provider
        r = QgsProviderRegistry.instance()
        metadata = QgsProviderMetadata(PyProvider.providerKey(), PyProvider.description(), PyProvider.createProvider)
        assert r.registerProvider(metadata)
        assert r.providerMetadata(PyProvider.providerKey()) == metadata

        # Create test layer
        cls.vl = cls.createLayer()
        assert (cls.vl.isValid())
        cls.source = cls.vl.dataProvider()

        # poly layer
        cls.poly_vl = QgsVectorLayer('Polygon?crs=epsg:4326&field=pk:integer&key=pk',
                                     'test', 'pythonprovider')
        assert (cls.poly_vl.isValid())
        cls.poly_provider = cls.poly_vl.dataProvider()

        f1 = QgsFeature()
        f1.setAttributes([1])
        f1.setGeometry(QgsGeometry.fromWkt('Polygon ((-69.03664108 81.35818902, -69.09237722 80.24346619, -73.718477 80.1319939, -73.718477 76.28620011, -74.88893598 76.34193625, -74.83319983 81.35818902, -69.03664108 81.35818902))'))

        f2 = QgsFeature()
        f2.setAttributes([2])
        f2.setGeometry(QgsGeometry.fromWkt('Polygon ((-67.58750139 81.1909806, -66.30557012 81.24671674, -66.30557012 76.89929767, -67.58750139 76.89929767, -67.58750139 81.1909806))'))

        f3 = QgsFeature()
        f3.setAttributes([3])
        f3.setGeometry(QgsGeometry.fromWkt('Polygon ((-68.36780737 75.78457483, -67.53176524 72.60761475, -68.64648808 73.66660144, -70.20710006 72.9420316, -68.36780737 75.78457483))'))

        f4 = QgsFeature()
        f4.setAttributes([4])

        cls.poly_provider.addFeatures([f1, f2, f3, f4])

    def testNoSliverPolygons(self):

        # create a layer with some polygons that will be used as a source for "avoid intersections"
        l = QgsVectorLayer('MultiPolygon', 'test_layer', 'memory')
        assert l.isValid()
        QgsProject.instance().addMapLayer(l)
        QgsProject.instance().writeEntry("Digitizing", "/AvoidIntersectionsList", [l.id()])

        features = []
        for i, wkt in enumerate(feat_wkt):
            f = QgsFeature(i + 1)
            f.setGeometry(QgsGeometry.fromWkt(wkt))
            features.append(f)

        l.dataProvider().addFeatures(features)
        assert l.pendingFeatureCount() == 7

        # create a geometry and remove its intersections with other geometries

        g = QgsGeometry.fromWkt(newg_wkt)
        assert g.avoidIntersections() == 0

        # the resulting multi-polygon must have exactly three parts
        # (in QGIS 2.0 it has one more tiny part that appears at the border between two of the original polygons)
        mpg = g.asMultiPolygon()
        assert len(mpg) == 3

    def testProxyFeatureSink(self):
        fields = QgsFields()
        fields.append(QgsField('fldtxt', QVariant.String))
        fields.append(QgsField('fldint', QVariant.Int))

        store = QgsFeatureStore(fields, QgsCoordinateReferenceSystem())
        proxy = QgsProxyFeatureSink(store)
        self.assertEqual(proxy.destinationSink(), store)

        self.assertEqual(len(store), 0)

        f = QgsFeature()
        f.setAttributes(["test", 123])
        f.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(100, 200)))
        proxy.addFeature(f)
        self.assertEqual(len(store), 1)
        self.assertEqual(store.features()[0]['fldtxt'], 'test')

        f2 = QgsFeature()
        f2.setAttributes(["test2", 457])
        f2.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(200, 200)))
        f3 = QgsFeature()
        f3.setAttributes(["test3", 888])
        f3.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(300, 200)))
        proxy.addFeatures([f2, f3])
        self.assertEqual(len(store), 3)
        self.assertEqual(store.features()[1]['fldtxt'], 'test2')
        self.assertEqual(store.features()[2]['fldtxt'], 'test3')

    def testDeleteMultipleFeatures(self):
        # test deleting multiple features from an edit buffer

        # make a layer with two features
        layer = createEmptyLayer()
        self.assertTrue(layer.startEditing())

        # add two features
        f1 = QgsFeature(layer.fields(), 1)
        f1.setGeometry(QgsGeometry.fromPoint(QgsPointXY(1, 2)))
        f1.setAttributes(["test", 123])
        self.assertTrue(layer.addFeature(f1))

        f2 = QgsFeature(layer.fields(), 2)
        f2.setGeometry(QgsGeometry.fromPoint(QgsPointXY(2, 4)))
        f2.setAttributes(["test2", 246])
        self.assertTrue(layer.addFeature(f2))

        layer.commitChanges()
        layer.startEditing()

        self.assertEqual(layer.editBuffer().deletedFeatureIds(), [])
        self.assertFalse(layer.editBuffer().isFeatureDeleted(1))
        self.assertFalse(layer.editBuffer().isFeatureDeleted(2))

        # delete features
        layer.deleteFeatures([1, 2])

        # test contents of buffer
        self.assertEqual(set(layer.editBuffer().deletedFeatureIds()), set([1, 2]))
        self.assertTrue(layer.editBuffer().isFeatureDeleted(1))
        self.assertTrue(layer.editBuffer().isFeatureDeleted(2))

    def testPartNum(self):
        # test geometry_part_num variable
        s = QgsLineSymbol()
        s.deleteSymbolLayer(0)

        sym_layer = QgsGeometryGeneratorSymbolLayer.create({'geometryModifier': 'segments_to_lines($geometry)'})
        sym_layer.setSymbolType(QgsSymbol.Line)
        s.appendSymbolLayer(sym_layer)

        marker_line = QgsMarkerLineSymbolLayer(False)
        marker_line.setPlacement(QgsMarkerLineSymbolLayer.FirstVertex)
        f = QgsFontUtils.getStandardTestFont('Bold', 24)
        marker = QgsFontMarkerSymbolLayer(f.family(), 'x', 24, QColor(255, 255, 0))
        marker.setDataDefinedProperty(QgsSymbolLayer.PropertyCharacter, QgsProperty.fromExpression('@geometry_part_num'))
        marker_symbol = QgsMarkerSymbol()
        marker_symbol.changeSymbolLayer(0, marker)
        marker_line.setSubSymbol(marker_symbol)
        marker_line.setAverageAngleLength(0)
        line_symbol = QgsLineSymbol()
        line_symbol.changeSymbolLayer(0, marker_line)
        sym_layer.setSubSymbol(line_symbol)

        # rendering test
        g = QgsGeometry.fromWkt('LineString(0 0, 10 0, 10 10, 0 10)')
        rendered_image = self.renderGeometry(s, g, buffer=4)
        assert self.imageCheck('part_num_variable', 'part_num_variable', rendered_image)

        marker.setDataDefinedProperty(QgsSymbolLayer.PropertyCharacter,
                                      QgsProperty.fromExpression('@geometry_part_count'))

        # rendering test
        g = QgsGeometry.fromWkt('LineString(0 0, 10 0, 10 10, 0 10)')
        rendered_image = self.renderGeometry(s, g, buffer=4)
        assert self.imageCheck('part_count_variable', 'part_count_variable', rendered_image)

    def processAlgorithm(self, parameters, context, feedback):
        spacing = self.parameterAsDouble(parameters, self.SPACING, context)
        inset = self.parameterAsDouble(parameters, self.INSET, context)
        randomize = self.parameterAsBool(parameters, self.RANDOMIZE, context)
        isSpacing = self.parameterAsBool(parameters, self.IS_SPACING, context)
        crs = self.parameterAsCrs(parameters, self.CRS, context)
        extent = self.parameterAsExtent(parameters, self.EXTENT, context, crs)

        fields = QgsFields()
        fields.append(QgsField('id', QVariant.Int, '', 10, 0))

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

        if randomize:
            seed()

        area = extent.width() * extent.height()
        if isSpacing:
            pSpacing = spacing
        else:
            pSpacing = sqrt(area / spacing)

        f = QgsFeature()
        f.initAttributes(1)
        f.setFields(fields)

        count = 0
        total = 100.0 / (area / pSpacing)
        y = extent.yMaximum() - inset

        extent_geom = QgsGeometry.fromRect(extent)
        extent_engine = QgsGeometry.createGeometryEngine(extent_geom.constGet())
        extent_engine.prepareGeometry()

        while y >= extent.yMinimum():
            x = extent.xMinimum() + inset
            while x <= extent.xMaximum():
                if feedback.isCanceled():
                    break

                if randomize:
                    geom = QgsGeometry().fromPointXY(QgsPointXY(
                        uniform(x - (pSpacing / 2.0), x + (pSpacing / 2.0)),
                        uniform(y - (pSpacing / 2.0), y + (pSpacing / 2.0))))
                else:
                    geom = QgsGeometry().fromPointXY(QgsPointXY(x, y))

                if extent_engine.intersects(geom.constGet()):
                    f.setAttribute('id', count)
                    f.setGeometry(geom)
                    sink.addFeature(f, QgsFeatureSink.FastInsert)
                    x += pSpacing
                    count += 1
                    feedback.setProgress(int(count * total))
            y = y - pSpacing

        return {self.OUTPUT: dest_id}

    def _rectangleGridLine(self, writer, width, height, originX, originY,
                           hSpacing, vSpacing):
        ft = QgsFeature()

        columns = int(math.floor(float(width) / hSpacing))
        rows = int(math.floor(float(height) / vSpacing))

        # Longitude lines
        for col in xrange(0, columns + 1):
            polyline = []
            x = originX + (col * hSpacing)
            for row in xrange(0, rows + 1):
                y = originY + (row * vSpacing)
                polyline.append(QgsPoint(x, y))

            ft.setGeometry(QgsGeometry.fromPolyline(polyline))
            ft.setAttributes([x, originY, x, originY + (rows * vSpacing)])
            writer.addFeature(ft)

        # Latitude lines
        for row in xrange(0, rows + 1):
            polyline = []
            y = originY + (row * vSpacing)
            for col in xrange(0, columns + 1):
                x = originX + (col * hSpacing)
                polyline.append(QgsPoint(x, y))

            ft.setGeometry(QgsGeometry.fromPolyline(polyline))
            ft.setAttributes([originX, y, originX + (col * hSpacing), y])
            writer.addFeature(ft)

    def processAlgorithm(self, progress):
        layer = dataobjects.getObjectFromUri(self.getParameterValue(self.INPUT))
        tolerance = self.getParameterValue(self.TOLERANCE)

        pointsBefore = 0
        pointsAfter = 0

        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
            layer.pendingFields().toList(), layer.wkbType(), layer.crs())

        features = vector.features(layer)
        total = 100.0 / len(features)
        for current, f in enumerate(features):
            featGeometry = QgsGeometry(f.geometry())
            attrs = f.attributes()
            pointsBefore += self.geomVertexCount(featGeometry)
            newGeometry = featGeometry.simplify(tolerance)
            pointsAfter += self.geomVertexCount(newGeometry)
            feature = QgsFeature()
            feature.setGeometry(newGeometry)
            feature.setAttributes(attrs)
            writer.addFeature(feature)
            progress.setPercentage(int(current * total))

        del writer

        ProcessingLog.addToLog(ProcessingLog.LOG_INFO,
                               self.tr('Simplify: Input geometries have been simplified from %s to %s points' % (pointsBefore, pointsAfter)))

    def diamonds(self, writer, features, width, height, rotation):
        ft = QgsFeature()

        xOffset = width / 2.0
        yOffset = height / 2.0

        if rotation is not None:
            phi = rotation * math.pi / 180
            for current, feat in enumerate(features):
                point = feat.geometry().asPoint()
                x = point.x()
                y = point.y()
                points = [(0.0, -yOffset), (-xOffset, 0.0), (0.0, yOffset), (xOffset, 0.0)]
                polygon = [[QgsPoint(i[0] * math.cos(phi) + i[1] * math.sin(phi) + x,
                                     -i[0] * math.sin(phi) + i[1] * math.cos(phi) + y) for i in points]]

                ft.setGeometry(QgsGeometry.fromPolygon(polygon))
                ft.setAttributes(feat.attributes())
                writer.addFeature(ft)
        else:
            for current, feat in enumerate(features):
                point = feat.geometry().asPoint()
                x = point.x()
                y = point.y()
                points = [(0.0, -yOffset), (-xOffset, 0.0), (0.0, yOffset), (xOffset, 0.0)]
                polygon = [[QgsPoint(i[0] + x, i[1] + y) for i in points]]

                ft.setGeometry(QgsGeometry.fromPolygon(polygon))
                ft.setAttributes(feat.attributes())
                writer.addFeature(ft)

    def ovals(self, writer, features, width, height, rotation, segments):
        ft = QgsFeature()

        xOffset = width / 2.0
        yOffset = height / 2.0

        if rotation is not None:
            phi = rotation * math.pi / 180
            for current, feat in enumerate(features):
                point = feat.geometry().asPoint()
                x = point.x()
                y = point.y()
                points = []
                for t in [(2 * math.pi) / segments * i for i in range(segments)]:
                    points.append((xOffset * math.cos(t), yOffset * math.sin(t)))
                polygon = [[QgsPoint(i[0] * math.cos(phi) + i[1] * math.sin(phi) + x,
                                     -i[0] * math.sin(phi) + i[1] * math.cos(phi) + y) for i in points]]

                ft.setGeometry(QgsGeometry.fromPolygon(polygon))
                ft.setAttributes(feat.attributes())
                writer.addFeature(ft)
        else:
            for current, feat in enumerate(features):
                point = feat.geometry().asPoint()
                x = point.x()
                y = point.y()
                points = []
                for t in [(2 * math.pi) / segments * i for i in range(segments)]:
                    points.append((xOffset * math.cos(t), yOffset * math.sin(t)))
                polygon = [[QgsPoint(i[0] + x, i[1] + y) for i in points]]

                ft.setGeometry(QgsGeometry.fromPolygon(polygon))
                ft.setAttributes(feat.attributes())
                writer.addFeature(ft)

    def processAlgorithm(self, parameters, context, feedback):
        layerA = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(Difference.INPUT), context)
        layerB = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(Difference.OVERLAY), context)

        geomType = QgsWkbTypes.multiType(layerA.wkbType())
        writer = self.getOutputFromName(
            Difference.OUTPUT).getVectorWriter(layerA.fields(), geomType, layerA.crs(), context)

        outFeat = QgsFeature()
        index = QgsProcessingUtils.createSpatialIndex(layerB, context)
        selectionA = QgsProcessingUtils.getFeatures(layerA, context)
        total = 100.0 / layerA.featureCount() if layerA.featureCount() else 0
        for current, inFeatA in enumerate(selectionA):
            geom = inFeatA.geometry()
            diff_geom = QgsGeometry(geom)
            attrs = inFeatA.attributes()
            intersections = index.intersects(geom.boundingBox())

            request = QgsFeatureRequest().setFilterFids(intersections).setSubsetOfAttributes([])
            for inFeatB in layerB.getFeatures(request):
                tmpGeom = inFeatB.geometry()
                if diff_geom.intersects(tmpGeom):
                    diff_geom = QgsGeometry(diff_geom.difference(tmpGeom))

            try:
                outFeat.setGeometry(diff_geom)
                outFeat.setAttributes(attrs)
                writer.addFeature(outFeat, QgsFeatureSink.FastInsert)
            except:
                QgsMessageLog.logMessage(self.tr('Feature geometry error: One or more output features ignored due to invalid geometry.'), self.tr('Processing'), QgsMessageLog.WARNING)
                continue

            feedback.setProgress(int(current * total))

        del writer

    def test_snappointstogrid(self):
        """Check that this runs correctly"""

        polygon_layer = self._make_layer('Polygon')
        f1 = QgsFeature(polygon_layer.fields())
        f1.setAttributes([1])
        f1.setGeometry(QgsGeometry.fromWkt('POLYGON((1.2 1.2, 1.2 2.2, 2.2 2.2, 2.2 1.2, 1.2 1.2))'))
        f2 = QgsFeature(polygon_layer.fields())
        f2.setAttributes([2])
        f2.setGeometry(QgsGeometry.fromWkt('POLYGON((1.1 1.1, 1.1 2.1, 2.1 2.1, 2.1 1.1, 1.1 1.1))'))
        self.assertTrue(f2.isValid())
        self.assertTrue(polygon_layer.startEditing())
        self.assertTrue(polygon_layer.addFeatures([f1, f2]))
        self.assertEqual(polygon_layer.featureCount(), 2)
        polygon_layer.commitChanges()
        self.assertEqual(polygon_layer.featureCount(), 2)
        QgsProject.instance().addMapLayers([polygon_layer])

        polygon_layer.selectByIds([next(polygon_layer.getFeatures()).id()])
        self.assertEqual(polygon_layer.selectedFeatureCount(), 1)

        old_features, new_features = self._alg_tester(
            'native:snappointstogrid',
            polygon_layer,
            {
                'HSPACING': 0.5,
                'VSPACING': 0.5,
            }
        )

        g = [f.geometry() for f in new_features][0]
        self.assertEqual(g.asWkt(), 'Polygon ((1 1, 1 2, 2 2, 2 1, 1 1))')
        # Check selected
        self.assertEqual(polygon_layer.selectedFeatureIds(), [1])

 def linearMatrix(self, writer, provider1, provider2, index1, index2, nearest, distArea, matType, sindex, progressBar):
     inFeat = QgsFeature()
     outFeat = QgsFeature()
     inGeom = QgsGeometry()
     outGeom = QgsGeometry()
     start = 15.00
     add = 85.00 / provider1.featureCount()
     fit1 = provider1.getFeatures()
     while fit1.nextFeature(inFeat):
         inGeom = inFeat.geometry()
         inID = inFeat.attributes()[index1]
         featList = sindex.nearestNeighbor(inGeom.asPoint(), nearest)
         distList = []
         vari = 0.00
         for i in featList:
             provider2.getFeatures(QgsFeatureRequest().setFilterFid(int(i)).setSubsetOfAttributes([index2])).nextFeature(outFeat)
             outID = outFeat.attributes()[index2]
             outGeom = outFeat.geometry()
             dist = distArea.measureLine(inGeom.asPoint(), outGeom.asPoint())
             if dist > 0:
                 if matType == "Linear":
                     writer.writerow([unicode(inID), unicode(outID), unicode(dist)])
                 else:
                     distList.append(float(dist))
         if matType == "Summary":
             mean = sum(distList) / len(distList)
             for i in distList:
                 vari = vari + ((i - mean) * (i - mean))
             vari = sqrt(vari / len(distList))
             writer.writerow([unicode(inID), unicode(mean), unicode(vari), unicode(min(distList)), unicode(max(distList))])
         start = start + add
         progressBar.setValue(start)
     del writer

 def densifyGeometry(self, geometry, pointsNumber, isPolygon):
     output = []
     if isPolygon:
         if geometry.isMultipart():
             polygons = geometry.asMultiPolygon()
             for poly in polygons:
                 p = []
                 for ring in poly:
                     p.append(self.densify(ring, pointsNumber))
                 output.append(p)
             return QgsGeometry.fromMultiPolygon(output)
         else:
             rings = geometry.asPolygon()
             for ring in rings:
                 output.append(self.densify(ring, pointsNumber))
             return QgsGeometry.fromPolygon(output)
     else:
         if geometry.isMultipart():
             lines = geometry.asMultiPolyline()
             for points in lines:
                 output.append(self.densify(points, pointsNumber))
             return QgsGeometry.fromMultiPolyline(output)
         else:
             points = geometry.asPolyline()
             output = self.densify(points, pointsNumber)
             return QgsGeometry.fromPolyline(output)

    def layerOmmb(self, layer, writer, feedback):
        req = QgsFeatureRequest().setSubsetOfAttributes([])
        features = vector.features(layer, req)
        total = 100.0 / len(features)
        newgeometry = QgsGeometry()
        first = True
        for current, inFeat in enumerate(features):
            if first:
                newgeometry = inFeat.geometry()
                first = False
            else:
                newgeometry = newgeometry.combine(inFeat.geometry())
            feedback.setProgress(int(current * total))

        geometry, area, angle, width, height = newgeometry.orientedMinimumBoundingBox()

        if geometry:
            outFeat = QgsFeature()

            outFeat.setGeometry(geometry)
            outFeat.setAttributes([area,
                                   width * 2 + height * 2,
                                   angle,
                                   width,
                                   height])
            writer.addFeature(outFeat)

def union_geometry(vector, request=QgsFeatureRequest()):
    """Return union of the vector geometries regardless of the attributes.
    (If request is specified, filter the objects before union).
    If all geometries in the vector are invalid, return None.

    The boundaries will be dissolved during the operation.

    :param vector:  Vector layer
    :type vector:   QgsVectorLayer

    :param request: Filter for vector objects
    :type request:  QgsFeatureRequest

    :return:        Union of the geometry
    :rtype:         QgsGeometry or None
    """

    result_geometry = None
    for feature in vector.getFeatures(request):
        if result_geometry is None:
            result_geometry = QgsGeometry(feature.geometry())
        else:
            # But some feature.geometry() may be invalid, skip them
            tmp_geometry = result_geometry.combine(feature.geometry())
            try:
                if tmp_geometry.isGeosValid():
                    result_geometry = tmp_geometry
            except AttributeError:
                pass
    return result_geometry

    def test_check_validity(self):
        """Test that the output invalid contains the error reason"""

        polygon_layer = self._make_layer('Polygon')
        self.assertTrue(polygon_layer.startEditing())
        f = QgsFeature(polygon_layer.fields())
        f.setAttributes([1])
        # Flake!
        f.setGeometry(QgsGeometry.fromWkt(
            'POLYGON ((0 0, 2 2, 0 2, 2 0, 0 0))'))
        self.assertTrue(f.isValid())
        f2 = QgsFeature(polygon_layer.fields())
        f2.setAttributes([1])
        f2.setGeometry(QgsGeometry.fromWkt(
            'POLYGON((1.1 1.1, 1.1 2.1, 2.1 2.1, 2.1 1.1, 1.1 1.1))'))
        self.assertTrue(f2.isValid())
        self.assertTrue(polygon_layer.addFeatures([f, f2]))
        polygon_layer.commitChanges()
        polygon_layer.rollBack()
        self.assertEqual(polygon_layer.featureCount(), 2)

        QgsProject.instance().addMapLayers([polygon_layer])

        alg = self.registry.createAlgorithmById('qgis:checkvalidity')

        context = QgsProcessingContext()
        context.setProject(QgsProject.instance())
        feedback = ConsoleFeedBack()

        self.assertIsNotNone(alg)
        parameters = {}
        parameters['INPUT_LAYER'] = polygon_layer.id()
        parameters['VALID_OUTPUT'] = 'memory:'
        parameters['INVALID_OUTPUT'] = 'memory:'
        parameters['ERROR_OUTPUT'] = 'memory:'

        # QGIS method
        parameters['METHOD'] = 1
        ok, results = execute(
            alg, parameters, context=context, feedback=feedback)
        self.assertTrue(ok)
        invalid_layer = QgsProcessingUtils.mapLayerFromString(
            results['INVALID_OUTPUT'], context)
        self.assertEqual(invalid_layer.fields().names()[-1], '_errors')
        self.assertEqual(invalid_layer.featureCount(), 1)
        f = next(invalid_layer.getFeatures())
        self.assertEqual(f.attributes(), [
                         1, 'segments 0 and 2 of line 0 intersect at 1, 1'])

        # GEOS method
        parameters['METHOD'] = 2
        ok, results = execute(
            alg, parameters, context=context, feedback=feedback)
        self.assertTrue(ok)
        invalid_layer = QgsProcessingUtils.mapLayerFromString(
            results['INVALID_OUTPUT'], context)
        self.assertEqual(invalid_layer.fields().names()[-1], '_errors')
        self.assertEqual(invalid_layer.featureCount(), 1)
        f = next(invalid_layer.getFeatures())
        self.assertEqual(f.attributes(), [1, 'Self-intersection'])

    def layerOmmb(self, layer, writer, progress):
        current = 0

        fit = layer.getFeatures()
        inFeat = QgsFeature()
        total = 100.0 / layer.featureCount()
        newgeometry = QgsGeometry()
        first = True
        while fit.nextFeature(inFeat):
            if first:
                newgeometry = inFeat.geometry()
                first = False
            else:
                newgeometry = newgeometry.combine(inFeat.geometry())
            current += 1
            progress.setPercentage(int(current * total))

        geometry, area, perim, angle, width, height = self.OMBBox(newgeometry)

        if geometry:
            outFeat = QgsFeature()

            outFeat.setGeometry(geometry)
            outFeat.setAttributes([area,
                                   perim,
                                   angle,
                                   width,
                                   height])
            writer.addFeature(outFeat)

  def __init__(self, xmin, ymin, xmax, ymax, x_segments, y_segments):
    self.vbands = []
    self.hbands = []
    self.vidx = QgsSpatialIndex()
    self.hidx = QgsSpatialIndex()

    xres = (xmax - xmin) / x_segments
    yres = (ymax - ymin) / y_segments
    self.xmin, self.ymax, self.xres, self.yres = xmin, ymax, xres, yres

    def addVBand(idx, geom):
      f = QgsFeature(idx)
      f.setGeometry(geom)
      self.vbands.append(f)
      self.vidx.insertFeature(f)

    def addHBand(idx, geom):
      f = QgsFeature(idx)
      f.setGeometry(geom)
      self.hbands.append(f)
      self.hidx.insertFeature(f)

    for x in range(x_segments):
      addVBand(x, QgsGeometry.fromRect(QgsRectangle(xmin + x * xres, ymin, xmin + (x + 1) * xres, ymax)))

    for y in range(y_segments):
      addHBand(y, QgsGeometry.fromRect(QgsRectangle(xmin, ymax - (y + 1) * yres, xmax, ymax - y * yres)))