ベクターレイヤーを使う¶

属性に関する情報を取得する
ベクターレイヤーの反復処理
地物の選択
ベクターレイヤーを修正する
空間索引を使う
Creating Vector Layers
ベクタレイヤの表現(シンボロジ)
より詳しいトピック

このセクションではベクターレイヤーに対して行える様々な操作について紹介していきます.

Most work here is based on the methods of the QgsVectorLayer class.

属性に関する情報を取得する ¶

You can retrieve information about the fields associated with a vector layer by calling fields() on a QgsVectorLayer object:

# "layer" is a QgsVectorLayer instance
for field in layer.fields():
    print(field.name(), field.typeName())

Iterating over the features in a vector layer is one of the most common tasks. Below is an example of the simple basic code to perform this task and showing some information about each feature. The layer variable is assumed to have a QgsVectorLayer object.

layer = iface.activeLayer()
features = layer.getFeatures()

for feature in features:
    # retrieve every feature with its geometry and attributes
    print("Feature ID: ", feature.id())
    # fetch geometry
    # show some information about the feature geometry
    geom = feature.geometry()
    geomSingleType = QgsWkbTypes.isSingleType(geom.wkbType())
    if geom.type() == QgsWkbTypes.PointGeometry:
        # the geometry type can be of single or multi type
        if geomSingleType:
            x = geom.asPoint()
            print("Point: ", x)
        else:
            x = geom.asMultiPoint()
            print("MultiPoint: ", x)
    elif geom.type() == QgsWkbTypes.LineGeometry:
        if geomSingleType:
            x = geom.asPolyline()
            print("Line: ", x, "length: ", geom.length())
        else:
            x = geom.asMultiPolyline()
            print("MultiLine: ", x, "length: ", geom.length())
    elif geom.type() == QgsWkbTypes.PolygonGeometry:
        if geomSingleType:
            x = geom.asPolygon()
            print("Polygon: ", x, "Area: ", geom.area())
        else:
            x = geom.asMultiPolygon()
            print("MultiPolygon: ", x, "Area: ", geom.area())
    else:
        print("Unknown or invalid geometry")
    # fetch attributes
    attrs = feature.attributes()
    # attrs is a list. It contains all the attribute values of this feature
    print(attrs)

地物の選択 ¶

In QGIS desktop, features can be selected in different ways: the user can click on a feature, draw a rectangle on the map canvas or use an expression filter. Selected features are normally highlighted in a different color (default is yellow) to draw user's attention on the selection.

Sometimes it can be useful to programmatically select features or to change the default color.

To select all the features, the selectAll() method can be used:

# Get the active layer (must be a vector layer)
layer = iface.activeLayer()
layer.selectAll()

To select using an expression, use the selectByExpression() method:

# Assumes that the active layer is points.shp file from the QGIS test suite
# (Class (string) and Heading (number) are attributes in points.shp)
layer = iface.activeLayer()
layer.selectByExpression('"Class"=\'B52\' and "Heading" > 10 and "Heading" <70', QgsVectorLayer.SetSelection)

To change the selection color you can use setSelectionColor() method of QgsMapCanvas as shown in the following example:

iface.mapCanvas().setSelectionColor( QColor("red") )

To add features to the selected features list for a given layer, you can call select() passing to it the list of features IDs:

selected_fid = []

# Get the first feature id from the layer
for feature in layer.getFeatures():
    selected_fid.append(feature.id())
    break

# Add these features to the selected list
layer.select(selected_fid)

To clear the selection:

layer.removeSelection()

属性にアクセスする ¶

Attributes can be referred to by their name:

print(feature['name'])

Alternatively, attributes can be referred to by index. This is a bit faster than using the name. For example, to get the first attribute:

print(feature[0])

選択された地物への反復処理 ¶

If you only need selected features, you can use the selectedFeatures() method from the vector layer:

selection = layer.selectedFeatures()
print(len(selection))
for feature in selection:
    # do whatever you need with the feature

一部の地物への反復処理 ¶

If you want to iterate over a given subset of features in a layer, such as those within a given area, you have to add a QgsFeatureRequest object to the getFeatures() call. Here's an example:

areaOfInterest = QgsRectangle(450290,400520, 450750,400780)

request = QgsFeatureRequest().setFilterRect(areaOfInterest)

for feature in layer.getFeatures(request):
    # do whatever you need with the feature

For the sake of speed, the intersection is often done only using feature’s bounding box. There is however a flag ExactIntersect that makes sure that only intersecting features will be returned:

request = QgsFeatureRequest().setFilterRect(areaOfInterest).setFlags(QgsFeatureRequest.ExactIntersect)

With setLimit() you can limit the number of requested features. Here's an example:

request = QgsFeatureRequest()
request.setLimit(2)
for feature in layer.getFeatures(request):
    # loop through only 2 features

If you need an attribute-based filter instead (or in addition) of a spatial one like shown in the examples above, you can build a QgsExpression object and pass it to the QgsFeatureRequest constructor. Here's an example:

# The expression will filter the features where the field "location_name"
# contains the word "Lake" (case insensitive)
exp = QgsExpression('location_name ILIKE \'%Lake%\'')
request = QgsFeatureRequest(exp)

See 式、フィルタ適用および値の算出 for the details about the syntax supported by QgsExpression.

要求は、地物ごとに取得したデータを定義するために使用できるので、反復子はすべての地物を返しますが、それぞれの地物については部分的データを返します。

# Only return selected fields to increase the "speed" of the request
request.setSubsetOfAttributes([0,2])

# More user friendly version
request.setSubsetOfAttributes(['name','id'],layer.fields())

# Don't return geometry objects to increase the "speed" of the request
request.setFlags(QgsFeatureRequest.NoGeometry)

# Fetch only the feature with id 45
request.setFilterFid(45)

# The options may be chained
request.setFilterRect(areaOfInterest).setFlags(QgsFeatureRequest.NoGeometry).setFilterFid(45).setSubsetOfAttributes([0,2])

ベクターレイヤーを修正する ¶

Most vector data providers support editing of layer data. Sometimes they support just a subset of possible editing actions. Use the capabilities() function to find out what set of functionality is supported.

caps = layer.dataProvider().capabilities()
# Check if a particular capability is supported:
if caps & QgsVectorDataProvider.DeleteFeatures:
    print('The layer supports DeleteFeatures')

For a list of all available capabilities, please refer to the API Documentation of QgsVectorDataProvider.

To print layer's capabilities textual description in a comma separated list you can use capabilitiesString() as in the following example:

caps_string = layer.dataProvider().capabilitiesString()
# Print:
# 'Add Features, Delete Features, Change Attribute Values, Add Attributes,
# Delete Attributes, Rename Attributes, Fast Access to Features at ID,
# Presimplify Geometries, Presimplify Geometries with Validity Check,
# Transactions, Curved Geometries'

ベクターレイヤーを編集するための以下の方法のいずれかを使用することで、変更は直接基礎となるデータストア（ファイル、データベースなど）にコミットされます。一時的な変更をしたいだけの場合は、どうするかを説明している次のセクション編集バッファで変更するに跳んでください。

注釈

QGISの内部（コンソールまたはプラグインからのいずれか）で作業している場合、ジオメトリ、スタイル、属性に行われた変更を確認するため、地図キャンバスを強制的に再描画することが必要になることもあるでしょう:

# If caching is enabled, a simple canvas refresh might not be sufficient
# to trigger a redraw and you must clear the cached image for the layer
if iface.mapCanvas().isCachingEnabled():
    layer.triggerRepaint()
else:
    iface.mapCanvas().refresh()

地物の追加 ¶

Create some QgsFeature instances and pass a list of them to provider's addFeatures() method. It will return two values: result (true/false) and list of added features (their ID is set by the data store).

To set up the attributes of the feature, you can either initialize the feature passing a QgsFields object (you can obtain that from the fields() method of the vector layer) or call initAttributes() passing the number of fields you want to be added.

if caps & QgsVectorDataProvider.AddFeatures:
    feat = QgsFeature(layer.fields())
    feat.setAttributes([0, 'hello'])
    # Or set a single attribute by key or by index:
    feat.setAttribute('name', 'hello')
    feat.setAttribute(0, 'hello')
    feat.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(123, 456)))
    (res, outFeats) = layer.dataProvider().addFeatures([feat])

地物の削除 ¶

To delete some features, just provide a list of their feature IDs.

if caps & QgsVectorDataProvider.DeleteFeatures:
    res = layer.dataProvider().deleteFeatures([5, 10])

地物の修正 ¶

It is possible to either change feature's geometry or to change some attributes. The following example first changes values of attributes with index 0 and 1, then it changes the feature's geometry.

fid = 100   # ID of the feature we will modify

if caps & QgsVectorDataProvider.ChangeAttributeValues:
    attrs = { 0 : "hello", 1 : 123 }
    layer.dataProvider().changeAttributeValues({ fid : attrs })

if caps & QgsVectorDataProvider.ChangeGeometries:
    geom = QgsGeometry.fromPointXY(QgsPointXY(111,222))
    layer.dataProvider().changeGeometryValues({ fid : geom })

ちなみに

Favor QgsVectorLayerEditUtils class for geometry-only edits

If you only need to change geometries, you might consider using the QgsVectorLayerEditUtils which provides some useful methods to edit geometries (translate, insert or move vertex, etc.).

ベクターレイヤーを編集バッファで修正する ¶

When editing vectors within QGIS application, you have to first start editing mode for a particular layer, then do some modifications and finally commit (or rollback) the changes. All the changes you make are not written until you commit them --- they stay in layer's in-memory editing buffer. It is possible to use this functionality also programmatically --- it is just another method for vector layer editing that complements the direct usage of data providers. Use this option when providing some GUI tools for vector layer editing, since this will allow user to decide whether to commit/rollback and allows the usage of undo/redo. When changes are commited, all changes from the editing buffer are saved to data provider.

The methods are similar to the ones we have seen in the provider, but they are called on the QgsVectorLayer object instead.

For these methods to work, the layer must be in editing mode. To start the editing mode, use the startEditing() method. To stop editing, use the commitChanges() or rollBack() methods. The first one will commit all your changes to the data source, while the second one will discard them and will not modify the data source at all.

To find out whether a layer is in editing mode, use the isEditable() method.

Here you have some examples that demonstrate how to use these editing methods.

from qgis.PyQt.QtCore import QVariant

# add two features (QgsFeature instances)
layer.addFeatures([feat1,feat2])
# delete a feature with specified ID
layer.deleteFeature(fid)

# set new geometry (QgsGeometry instance) for a feature
layer.changeGeometry(fid, geometry)
# update an attribute with given field index (int) to a given value
layer.changeAttributeValue(fid, fieldIndex, value)

# add new field
layer.addAttribute(QgsField("mytext", QVariant.String))
# remove a field
layer.deleteAttribute(fieldIndex)

In order to make undo/redo work properly, the above mentioned calls have to be wrapped into undo commands. (If you do not care about undo/redo and want to have the changes stored immediately, then you will have easier work by editing with data provider.)

Here is how you can use the undo functionality:

layer.beginEditCommand("Feature triangulation")

# ... call layer's editing methods ...

if problem_occurred:
  layer.destroyEditCommand()
  return

# ... more editing ...

layer.endEditCommand()

The beginEditCommand() method will create an internal "active" command and will record subsequent changes in vector layer. With the call to endEditCommand() the command is pushed onto the undo stack and the user will be able to undo/redo it from GUI. In case something went wrong while doing the changes, the destroyEditCommand() method will remove the command and rollback all changes done while this command was active.

次の例に示すように、よりセマンティックなコードブロックにコミットとロールバックをラップする with edit(layer) 文も使用できます：

with edit(layer):
  feat = next(layer.getFeatures())
  feat[0] = 5
  layer.updateFeature(feat)

This will automatically call commitChanges() in the end. If any exception occurs, it will rollBack() all the changes. In case a problem is encountered within commitChanges() (when the method returns False) a QgsEditError exception will be raised.

フィールドを追加または削除する ¶

フィールド(属性)を追加するには、フィールドの定義の配列を指定する必要があります。フィールドを削除するにはフィールドの索引の配列を渡すだけです

from qgis.PyQt.QtCore import QVariant

if caps & QgsVectorDataProvider.AddAttributes:
    res = layer.dataProvider().addAttributes(
        [QgsField("mytext", QVariant.String),
        QgsField("myint", QVariant.Int)])

if caps & QgsVectorDataProvider.DeleteAttributes:
    res = layer.dataProvider().deleteAttributes([0])

データプロバイダーのフィールドを追加または削除した後、レイヤーのフィールドは、変更が自動的に反映されていないため、更新する必要があります。

layer.updateFields()

ちなみに

Directly save changes using with based command

Using with edit(layer): the changes will be commited automatically calling commitChanges() at the end. If any exception occurs, it will rollBack() all the changes. See ベクターレイヤーを編集バッファで修正する.

空間索引を使う ¶

空間索引は、頻繁にベクターレイヤーに問い合わせをする必要がある場合、コードのパフォーマンスを劇的に改善します。例えば、補間アルゴリズムを書いていて、補間値の計算に使用するために与えられた位置に対して最も近い10点をポイントレイヤーから求める必要がある、と想像してください。空間索引が無いと、QGISがこれらの10点を求める方法は、すべての点から指定の場所への距離を計算してそれらの距離を比較することしかありません。これは、いくつかの場所について繰り返す必要がある場合は特に、非常に時間のかかる処理となります。もし空間索引がレイヤーに作成されていれば、処理はもっと効率的になります。

空間索引の無いレイヤーは、電話番号が順番に並んでいない、もしくは索引の無い電話帳と思ってください。所定の人の電話番号を見つける唯一の方法は、巻頭からその番号を見つけるまで読むだけです。

空間索引は、QGISベクターレイヤーに対してデフォルトでは作成されていませんが、簡単に作成できます。しなければいけないことはこうです：

create spatial index using the QgsSpatialIndex() class:
```
index = QgsSpatialIndex()
```
add features to index --- index takes QgsFeature object and adds it to the internal data structure. You can create the object manually or use one from a previous call to the provider's getFeatures() method.
```
index.insertFeature(feat)
```
代わりに、一括読み込みを使用してレイヤーのすべての地物を一度に読み込むことができます
```
index = QgsSpatialIndex(layer.getFeatures())
```

空間索引に何かしらの値が入れられると検索ができるようになります

# returns array of feature IDs of five nearest features
nearest = index.nearestNeighbor(QgsPointXY(25.4, 12.7), 5)

# returns array of IDs of features which intersect the rectangle
intersect = index.intersects(QgsRectangle(22.5, 15.3, 23.1, 17.2))

Creating Vector Layers ¶

There are several ways to generate a vector layer dataset:

the QgsVectorFileWriter class: A convenient class for writing vector files to disk, using either a static call to writeAsVectorFormat() which saves the whole vector layer or creating an instance of the class and issue calls to addFeature(). This class supports all the vector formats that OGR supports (GeoPackage, Shapefile, GeoJSON, KML and others).
the QgsVectorLayer class: instantiates a data provider that interprets the supplied path (url) of the data source to connect to and access the data. It can be used to create temporary, memory-based layers (memory) and connect to OGR datasets (ogr), databases (postgres, spatialite, mysql, mssql) and more (wfs, gpx, delimitedtext...).

From an instance of `QgsVectorFileWriter`¶

# Write to a GeoPackage (default)
error = QgsVectorFileWriter.writeAsVectorFormat(layer,
                                                "/path/to/folder/my_data",
                                                "")
if error[0] == QgsVectorFileWriter.NoError:
    print("success!")

# Write to an ESRI Shapefile format dataset using UTF-8 text encoding
error = QgsVectorFileWriter.writeAsVectorFormat(layer,
                                                "/path/to/folder/my_esridata",
                                                "UTF-8",
                                                driverName="ESRI Shapefile")
if error[0] == QgsVectorFileWriter.NoError:
    print("success again!")

The third (mandatory) parameter specifies output text encoding. Only some drivers need this for correct operation - Shapefile is one of them (other drivers will ignore this parameter). Specifying the correct encoding is important if you are using international (non US-ASCII) characters.

# Write to an ESRI GDB file
opts = QgsVectorFileWriter.SaveVectorOptions()
opts.driverName = "FileGDB"
# if no geometry
opts.overrideGeometryType = QgsWkbTypes.NullGeometry
opts.actionOnExistingFile = QgsVectorFileWriter.ActionOnExistingFile.CreateOrOverwriteLayer
opts.layerName = 'my_new_layer_name'
error = QgsVectorFileWriter.writeAsVectorFormat(layer=vlayer,
                                                fileName=gdb_path,
                                                options=opts)
if error[0] == QgsVectorFileWriter.NoError:
  print("success!")
else:
  print(error)

You can also convert fields to make them compatible with different formats by using the FieldValueConverter. For example, to convert array variable types (e.g. in Postgres) to a text type, you can do the following:

LIST_FIELD_NAME = 'xxxx'

class ESRIValueConverter(QgsVectorFileWriter.FieldValueConverter):

  def __init__(self, layer, list_field):
    QgsVectorFileWriter.FieldValueConverter.__init__(self)
      self.layer = layer
      self.list_field_idx = self.layer.fields().indexFromName(list_field)

  def convert(self, fieldIdxInLayer, value):
    if fieldIdxInLayer == self.list_field_idx:
      return QgsListFieldFormatter().representValue(layer=vlayer,
                                                    fieldIndex=self.list_field_idx,
                                                    config={},
                                                    cache=None,
                                                    value=value)
    else:
      return value

  def fieldDefinition(self, field):
    idx = self.layer.fields().indexFromName(field.name())
    if idx == self.list_field_idx:
      return QgsField(LIST_FIELD_NAME, QVariant.String)
    else:
      return self.layer.fields()[idx]

converter = ESRIValueConverter(vlayer, LIST_FIELD_NAME)
#opts is a QgsVectorFileWriter.SaveVectorOptions as above
opts.fieldValueConverter = converter

A destination CRS may also be specified --- if a valid instance of QgsCoordinateReferenceSystem is passed as the fourth parameter, the layer is transformed to that CRS.

For valid driver names please call the supportedFiltersAndFormats method or consult the supported formats by OGR --- you should pass the value in the "Code" column as the driver name.

Optionally you can set whether to export only selected features, pass further driver-specific options for creation or tell the writer not to create attributes... There are a number of other (optional) parameters; see the QgsVectorFileWriter documentation for details.

Directly from features ¶

from qgis.PyQt.QtCore import QVariant

# define fields for feature attributes. A QgsFields object is needed
fields = QgsFields()
fields.append(QgsField("first", QVariant.Int))
fields.append(QgsField("second", QVariant.String))

""" create an instance of vector file writer, which will create the vector file.
Arguments:
1. path to new file (will fail if exists already)
2. encoding of the attributes
3. field map
4. geometry type - from WKBTYPE enum
5. layer's spatial reference (instance of
   QgsCoordinateReferenceSystem) - optional
6. driver name for the output file """

writer = QgsVectorFileWriter("my_shapes.shp", "UTF-8", fields, QgsWkbTypes.Point, driverName="ESRI Shapefile")

if writer.hasError() != QgsVectorFileWriter.NoError:
    print("Error when creating shapefile: ",  w.errorMessage())

# add a feature
fet = QgsFeature()

fet.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(10,10)))
fet.setAttributes([1, "text"])
writer.addFeature(fet)

# delete the writer to flush features to disk
del writer

From an instance of `QgsVectorLayer`¶

Among all the data providers supported by the QgsVectorLayer class, let's focus on the memory-based layers. Memory provider is intended to be used mainly by plugin or 3rd party app developers. It does not store data on disk, allowing developers to use it as a fast backend for some temporary layers.

プロバイダーは文字列と int と double をサポートします。

The memory provider also supports spatial indexing, which is enabled by calling the provider's createSpatialIndex() function. Once the spatial index is created you will be able to iterate over features within smaller regions faster (since it's not necessary to traverse all the features, only those in specified rectangle).

A memory provider is created by passing "memory" as the provider string to the QgsVectorLayer constructor.

The constructor also takes a URI defining the geometry type of the layer, one of: "Point", "LineString", "Polygon", "MultiPoint", "MultiLineString", "MultiPolygon" or "None".

URIではメモリプロバイダーの座標参照系、属性フィールド、インデックスを指定できます。構文は、

crs=definition: Specifies the coordinate reference system, where definition may be any of the forms accepted by QgsCoordinateReferenceSystem.createFromString
index=yes: プロバイダーが空間索引を使うことを指定します。
field=name:type(length,precision): レイヤーの属性を指定します。属性は名前を持ち、オプションとして型(integer, double, string)、長さ、および精度を持ちます。フィールドの定義は複数あってかまいません。

次のサンプルは全てのこれらのオプションを含んだURLです:

"Point?crs=epsg:4326&field=id:integer&field=name:string(20)&index=yes"

次のサンプルコードはメモリプロバイダーを作成してデータ投入をしている様子です:

from qgis.PyQt.QtCore import QVariant

# create layer
vl = QgsVectorLayer("Point", "temporary_points", "memory")
pr = vl.dataProvider()

# add fields
pr.addAttributes([QgsField("name", QVariant.String),
                    QgsField("age",  QVariant.Int),
                    QgsField("size", QVariant.Double)])
vl.updateFields() # tell the vector layer to fetch changes from the provider

# add a feature
fet = QgsFeature()
fet.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(10,10)))
fet.setAttributes(["Johny", 2, 0.3])
pr.addFeatures([fet])

# update layer's extent when new features have been added
# because change of extent in provider is not propagated to the layer
vl.updateExtents()

最後にやったことを全て確認していきましょう:

# show some stats
print("fields:", len(pr.fields()))
print("features:", pr.featureCount())
e = vl.extent()
print("extent:", e.xMinimum(), e.yMinimum(), e.xMaximum(), e.yMaximum())

# iterate over features
features = vl.getFeatures()
for fet in features:
    print("F:", fet.id(), fet.attributes(), fet.geometry().asPoint())

ベクタレイヤの表現(シンボロジ)¶

ベクタレイヤがレンダリングされるとき、データの表現はレイヤに関連付けられた レンダラー と シンボル によって決定されます。シンボルは地物の視覚的表現を処理するクラスで、レンダラはそれぞれの地物でどのシンボルが使われるかを決定します。

The renderer for a given layer can be obtained as shown below:

renderer = layer.renderer()

この参照を利用して、少しだけ探索してみましょう:

print("Type:", renderer.type())

There are several known renderer types available in the QGIS core library:

タイプ	クラス	詳細
単一シンボル	`QgsSingleSymbolRenderer`	全ての地物を同じシンボルでレンダリングします
分類されたシンボル	`QgsCategorizedSymbolRenderer`	カテゴリごとに違うシンボルを使って地物をレンダリングします
段階に分けられたシンボル	`QgsGraduatedSymbolRenderer`	それぞれの範囲の値によって違うシンボルを使って地物をレンダリングします

There might be also some custom renderer types, so never make an assumption there are just these types. You can query the application's QgsRendererRegistry to find out currently available renderers:

print(QgsApplication.rendererRegistry().renderersList())
# Print:
['nullSymbol',
'singleSymbol',
'categorizedSymbol',
'graduatedSymbol',
'RuleRenderer',
'pointDisplacement',
'pointCluster',
'invertedPolygonRenderer',
'heatmapRenderer',
'25dRenderer']

レンダラーの中身をテキストフォームにダンプできます --- デバッグ時に役に立つでしょう:

print(renderer.dump())

単一シンボルレンダラー ¶

You can get the symbol used for rendering by calling symbol() method and change it with setSymbol() method (note for C++ devs: the renderer takes ownership of the symbol.)

You can change the symbol used by a particular vector layer by calling setSymbol() passing an instance of the appropriate symbol instance. Symbols for point, line and polygon layers can be created by calling the createSimple() function of the corresponding classes QgsMarkerSymbol, QgsLineSymbol and QgsFillSymbol.

The dictionary passed to createSimple() sets the style properties of the symbol.

For example you can replace the symbol used by a particular point layer by calling setSymbol() passing an instance of a QgsMarkerSymbol, as in the following code example:

symbol = QgsMarkerSymbol.createSimple({'name': 'square', 'color': 'red'})
layer.renderer().setSymbol(symbol)
# show the change
layer.triggerRepaint()

name は、マーカーの形状を示しており、以下のいずれかとすることができます。

circle
square
cross
rectangle
diamond
pentagon
triangle
equilateral_triangle
star
regular_star
arrow
filled_arrowhead
x

To get the full list of properties for the first symbol layer of a symbol instance you can follow the example code:

print(layer.renderer().symbol().symbolLayers()[0].properties())
# Prints
{'angle': '0',
'color': '0,128,0,255',
'horizontal_anchor_point': '1',
'joinstyle': 'bevel',
'name': 'circle',
'offset': '0,0',
'offset_map_unit_scale': '0,0',
'offset_unit': 'MM',
'outline_color': '0,0,0,255',
'outline_style': 'solid',
'outline_width': '0',
'outline_width_map_unit_scale': '0,0',
'outline_width_unit': 'MM',
'scale_method': 'area',
'size': '2',
'size_map_unit_scale': '0,0',
'size_unit': 'MM',
'vertical_anchor_point': '1'}

いくつかのプロパティを変更したい場合に便利です:

# You can alter a single property...
layer.renderer().symbol().symbolLayer(0).setSize(3)
# ... but not all properties are accessible from methods,
# you can also replace the symbol completely:
props = layer.renderer().symbol().symbolLayer(0).properties()
props['color'] = 'yellow'
props['name'] = 'square'
layer.renderer().setSymbol(QgsMarkerSymbol.createSimple(props))
# show the changes
layer.triggerRepaint()

分類シンボルレンダラー ¶

When using a categorized renderer, you can query and set the attribute that is used for classification: use the classAttribute() and setClassAttribute() methods.

カテゴリの配列を取得するには

for cat in renderer.categories():
    print("{}: {} :: {}".format(cat.value(), cat.label(), cat.symbol()))

Where value() is the value used for discrimination between categories, label() is a text used for category description and symbol() method returns the assigned symbol.

The renderer usually stores also original symbol and color ramp which were used for the classification: sourceColorRamp() and sourceSymbol() methods.

段階シンボルレンダラー ¶

このレンダラーは先ほど扱ったカテゴリ分けシンボルのレンダラーととても似ていますが、クラスごとの一つの属性値の代わりに領域の値として動作し、そのため数字の属性のみ使うことができます。

レンダラーで使われている領域の多くの情報を見つけるには

for ran in renderer.ranges():
    print("{} - {}: {} {}".format(
        ran.lowerValue(),
        ran.upperValue(),
        ran.label(),
        ran.symbol()
      ))

you can again use the classAttribute (to find the classification attribute name), sourceSymbol and sourceColorRamp methods. Additionally there is the mode method which determines how the ranges were created: using equal intervals, quantiles or some other method.

もし連続値シンボルレンダラーを作ろうとしているのであれば次のスニペットの例で書かれているようにします(これはシンプルな二つのクラスを作成するものを取り上げています):

from qgis.PyQt import QtGui

myVectorLayer = QgsVectorLayer(myVectorPath, myName, 'ogr')
myTargetField = 'target_field'
myRangeList = []
myOpacity = 1
# Make our first symbol and range...
myMin = 0.0
myMax = 50.0
myLabel = 'Group 1'
myColour = QtGui.QColor('#ffee00')
mySymbol1 = QgsSymbol.defaultSymbol(myVectorLayer.geometryType())
mySymbol1.setColor(myColour)
mySymbol1.setOpacity(myOpacity)
myRange1 = QgsRendererRange(myMin, myMax, mySymbol1, myLabel)
myRangeList.append(myRange1)
#now make another symbol and range...
myMin = 50.1
myMax = 100
myLabel = 'Group 2'
myColour = QtGui.QColor('#00eeff')
mySymbol2 = QgsSymbol.defaultSymbol(
     myVectorLayer.geometryType())
mySymbol2.setColor(myColour)
mySymbol2.setOpacity(myOpacity)
myRange2 = QgsRendererRange(myMin, myMax, mySymbol2, myLabel)
myRangeList.append(myRange2)
myRenderer = QgsGraduatedSymbolRenderer('', myRangeList)
myRenderer.setMode(QgsGraduatedSymbolRenderer.EqualInterval)
myRenderer.setClassAttribute(myTargetField)

myVectorLayer.setRenderer(myRenderer)
QgsProject.instance().addMapLayer(myVectorLayer)

シンボルの操作 ¶

For representation of symbols, there is QgsSymbol base class with three derived classes:

QgsMarkerSymbol --- for point features
QgsLineSymbol --- for line features
QgsFillSymbol --- for polygon features

Every symbol consists of one or more symbol layers (classes derived from QgsSymbolLayer). The symbol layers do the actual rendering, the symbol class itself serves only as a container for the symbol layers.

Having an instance of a symbol (e.g. from a renderer), it is possible to explore it: the type method says whether it is a marker, line or fill symbol. There is a dump method which returns a brief description of the symbol. To get a list of symbol layers:

for i in range(symbol.symbolLayerCount()):
    lyr = symbol.symbolLayer(i)
    print("{}: {}".format(i, lyr.layerType()))

To find out symbol's color use color method and setColor to change its color. With marker symbols additionally you can query for the symbol size and rotation with the size and angle methods. For line symbols the width method returns the line width.

サイズと幅は標準でミリメートルが使われ、角度は度が使われます。

シンボルレイヤーの操作 ¶

As said before, symbol layers (subclasses of QgsSymbolLayer) determine the appearance of the features. There are several basic symbol layer classes for general use. It is possible to implement new symbol layer types and thus arbitrarily customize how features will be rendered. The layerType() method uniquely identifies the symbol layer class --- the basic and default ones are SimpleMarker, SimpleLine and SimpleFill symbol layers types.

You can get a complete list of the types of symbol layers you can create for a given symbol layer class with the following code:

from qgis.core import QgsSymbolLayerRegistry
myRegistry = QgsApplication.symbolLayerRegistry()
myMetadata = myRegistry.symbolLayerMetadata("SimpleFill")
for item in myRegistry.symbolLayersForType(QgsSymbol.Marker):
    print(item)

Output:

EllipseMarker
FilledMarker
FontMarker
GeometryGenerator
SimpleMarker
SvgMarker
VectorField

The QgsSymbolLayerRegistry class manages a database of all available symbol layer types.

To access symbol layer data, use its properties() method that returns a key-value dictionary of properties which determine the appearance. Each symbol layer type has a specific set of properties that it uses. Additionally, there are the generic methods color, size, angle and width, with their setter counterparts. Of course size and angle are available only for marker symbol layers and width for line symbol layers.

カスタムシンボルレイヤータイプの作成 ¶

データをどうレンダリングするかをカスタマイズしたいと考えているとします。思うままに地物を描画する独自のシンボルレイヤークラスを作成できます。次の例は指定した半径で赤い円を描画するマーカーを示しています:

from qgis.core import QgsMarkerSymbolLayer
from qgis.PyQt.QtGui import QColor

class FooSymbolLayer(QgsMarkerSymbolLayer):

  def __init__(self, radius=4.0):
      QgsMarkerSymbolLayer.__init__(self)
      self.radius = radius
      self.color = QColor(255,0,0)

  def layerType(self):
     return "FooMarker"

  def properties(self):
      return { "radius" : str(self.radius) }

  def startRender(self, context):
    pass

  def stopRender(self, context):
      pass

  def renderPoint(self, point, context):
      # Rendering depends on whether the symbol is selected (QGIS >= 1.5)
      color = context.selectionColor() if context.selected() else self.color
      p = context.renderContext().painter()
      p.setPen(color)
      p.drawEllipse(point, self.radius, self.radius)

  def clone(self):
      return FooSymbolLayer(self.radius)

The layerType method determines the name of the symbol layer; it has to be unique among all symbol layers. The properties method is used for persistence of attributes. The clone method must return a copy of the symbol layer with all attributes being exactly the same. Finally there are rendering methods: startRender is called before rendering the first feature, stopRender when the rendering is done, and renderPoint is called to do the rendering. The coordinates of the point(s) are already transformed to the output coordinates.

For polylines and polygons the only difference would be in the rendering method: you would use renderPolyline which receives a list of lines, while renderPolygon receives a list of points on the outer ring as the first parameter and a list of inner rings (or None) as a second parameter.

普通はユーザーに外観をカスタマイズさせるためにシンボルレイヤータイプの属性を設定するGUIを追加すると使いやすくなります: 上記の例であればユーザーは円の半径を設定できます。次のコードはそのようなウィジェットの実装となります:

from qgis.gui import QgsSymbolLayerWidget

class FooSymbolLayerWidget(QgsSymbolLayerWidget):
    def __init__(self, parent=None):
        QgsSymbolLayerWidget.__init__(self, parent)

        self.layer = None

        # setup a simple UI
        self.label = QLabel("Radius:")
        self.spinRadius = QDoubleSpinBox()
        self.hbox = QHBoxLayout()
        self.hbox.addWidget(self.label)
        self.hbox.addWidget(self.spinRadius)
        self.setLayout(self.hbox)
        self.connect(self.spinRadius, SIGNAL("valueChanged(double)"), \
            self.radiusChanged)

    def setSymbolLayer(self, layer):
        if layer.layerType() != "FooMarker":
            return
        self.layer = layer
        self.spinRadius.setValue(layer.radius)

    def symbolLayer(self):
        return self.layer

    def radiusChanged(self, value):
        self.layer.radius = value
        self.emit(SIGNAL("changed()"))

This widget can be embedded into the symbol properties dialog. When the symbol layer type is selected in symbol properties dialog, it creates an instance of the symbol layer and an instance of the symbol layer widget. Then it calls the setSymbolLayer method to assign the symbol layer to the widget. In that method the widget should update the UI to reflect the attributes of the symbol layer. The symbolLayer method is used to retrieve the symbol layer again by the properties dialog to use it for the symbol.

On every change of attributes, the widget should emit the changed() signal to let the properties dialog update the symbol preview.

私達は最後につなげるところだけまだ扱っていません: QGIS にこれらの新しいクラスを知らせる方法です。これはレジストリにシンボルレイヤーを追加すれば完了です。レジストリに追加しなくてもシンボルレイヤーを使うことはできますが、いくつかの機能が動かないでしょう: 例えばカスタムシンボルレイヤーを使ってプロジェクトファイルを読み込んだり、GUIでレイヤーの属性を編集できないなど。

シンボルレイヤーのメタデータを作る必要があるでしょう

from qgis.core import QgsSymbol, QgsSymbolLayerAbstractMetadata, QgsSymbolLayerRegistry

class FooSymbolLayerMetadata(QgsSymbolLayerAbstractMetadata):

  def __init__(self):
    QgsSymbolLayerAbstractMetadata.__init__(self, "FooMarker", QgsSymbol.Marker)

  def createSymbolLayer(self, props):
    radius = float(props["radius"]) if "radius" in props else 4.0
    return FooSymbolLayer(radius)

      def createSymbolLayer(self, props):
        radius = float(props["radius"]) if "radius" in props else 4.0
        return FooSymbolLayer(radius)

QgsApplication.symbolLayerRegistry().addSymbolLayerType(FooSymbolLayerMetadata())

You should pass layer type (the same as returned by the layer) and symbol type (marker/line/fill) to the constructor of the parent class. The createSymbolLayer() method takes care of creating an instance of symbol layer with attributes specified in the props dictionary. And there is the createSymbolLayerWidget() method which returns the settings widget for this symbol layer type.

最後にこのシンボルレイヤーをレジストリに追加します --- これで完了です。

カスタムレンダラーの作成 ¶

もし地物をレンダリングするためのシンボルをどう選択するかをカスタマイズしたいのであれば、新しいレンダラーの実装を作ると便利かもしれません。いくつかのユースケースとしてこんなことをしたいのかもしれません: フィールドの組み合わせからシンボルを決定する、現在の縮尺に合わせてシンボルのサイズを変更するなどなど。

次のコードは二つのマーカーシンボルを作成して全ての地物からランダムに一つ選ぶ簡単なカスタムレンダラーです

import random
from qgis.core import QgsWkbTypes, QgsSymbol, QgsFeatureRenderer


class RandomRenderer(QgsFeatureRenderer):
  def __init__(self, syms=None):
    QgsFeatureRenderer.__init__(self, "RandomRenderer")
    self.syms = syms if syms else [QgsSymbol.defaultSymbol(QgsWkbTypes.geometryType(QgsWkbTypes.Point))]

  def symbolForFeature(self, feature):
    return random.choice(self.syms)

  def startRender(self, context, vlayer):
    for s in self.syms:
      s.startRender(context)

  def stopRender(self, context):
    for s in self.syms:
      s.stopRender(context)

  def usedAttributes(self):
    return []

  def clone(self):
    return RandomRenderer(self.syms)

from qgis.gui import QgsRendererWidget
class RandomRendererWidget(QgsRendererWidget):
  def __init__(self, layer, style, renderer):
    QgsRendererWidget.__init__(self, layer, style)
    if renderer is None or renderer.type() != "RandomRenderer":
      self.r = RandomRenderer()
    else:
      self.r = renderer
    # setup UI
    self.btn1 = QgsColorButton()
    self.btn1.setColor(self.r.syms[0].color())
    self.vbox = QVBoxLayout()
    self.vbox.addWidget(self.btn1)
    self.setLayout(self.vbox)
    self.btn1.clicked.connect(self.setColor1)

  def setColor1(self):
    color = QColorDialog.getColor(self.r.syms[0].color(), self)
    if not color.isValid(): return
    self.r.syms[0].setColor(color)
    self.btn1.setColor(self.r.syms[0].color())

  def renderer(self):
    return self.r

The constructor of the parent QgsFeatureRenderer class needs a renderer name (which has to be unique among renderers). The symbolForFeature method is the one that decides what symbol will be used for a particular feature. startRender and stopRender take care of initialization/finalization of symbol rendering. The usedAttributes method can return a list of field names that the renderer expects to be present. Finally, the clone method should return a copy of the renderer.

Like with symbol layers, it is possible to attach a GUI for configuration of the renderer. It has to be derived from QgsRendererWidget. The following sample code creates a button that allows the user to set the first symbol

from qgis.gui import QgsRendererWidget, QgsColorButton

class RandomRendererWidget(QgsRendererWidget):
  def __init__(self, layer, style, renderer):
    QgsRendererWidget.__init__(self, layer, style)
    if renderer is None or renderer.type() != "RandomRenderer":
      self.r = RandomRenderer()
    else:
      self.r = renderer
    # setup UI
    self.btn1 = QgsColorButton()
    self.btn1.setColor(self.r.syms[0].color())
    self.vbox = QVBoxLayout()
    self.vbox.addWidget(self.btn1)
    self.setLayout(self.vbox)
    self.connect(self.btn1, SIGNAL("clicked()"), self.setColor1)

  def setColor1(self):
    color = QColorDialog.getColor(self.r.syms[0].color(), self)
    if not color.isValid(): return
    self.r.syms[0].setColor(color)
    self.btn1.setColor(self.r.syms[0].color())

  def renderer(self):
    return self.r

The constructor receives instances of the active layer (QgsVectorLayer), the global style (QgsStyle) and the current renderer. If there is no renderer or the renderer has different type, it will be replaced with our new renderer, otherwise we will use the current renderer (which has already the type we need). The widget contents should be updated to show current state of the renderer. When the renderer dialog is accepted, the widget's renderer method is called to get the current renderer --- it will be assigned to the layer.

最後のちょっとした作業はレンダラーのメタデータとレジストリへの登録です。これらをしないとレンダラーのレイヤーの読み込みは動かず、ユーザーはレンダラーのリストから選択できないでしょう。では、私達の RandomRenderer の例を終わらせましょう

from qgis.core import QgsRendererAbstractMetadata,QgsRendererRegistry,QgsApplication

class RandomRendererMetadata(QgsRendererAbstractMetadata):
  def __init__(self):
    QgsRendererAbstractMetadata.__init__(self, "RandomRenderer", "Random renderer")

  def createRenderer(self, element):
    return RandomRenderer()
  def createRendererWidget(self, layer, style, renderer):
    return RandomRendererWidget(layer, style, renderer)

QgsApplication.rendererRegistry().addRenderer(RandomRendererMetadata())

Similarly as with symbol layers, abstract metadata constructor awaits renderer name, name visible for users and optionally name of renderer's icon. The createRenderer method passes a QDomElement instance that can be used to restore the renderer's state from the DOM tree. The createRendererWidget method creates the configuration widget. It does not have to be present or can return None if the renderer does not come with GUI.

To associate an icon with the renderer you can assign it in the QgsRendererAbstractMetadata constructor as a third (optional) argument --- the base class constructor in the RandomRendererMetadata __init__() function becomes

QgsRendererAbstractMetadata.__init__(self,
       "RandomRenderer",
       "Random renderer",
       QIcon(QPixmap("RandomRendererIcon.png", "png")))

The icon can also be associated at any later time using the setIcon method of the metadata class. The icon can be loaded from a file (as shown above) or can be loaded from a Qt resource (PyQt5 includes .qrc compiler for Python).

より詳しいトピック ¶

TODO:

シンボルの作成や修正
working with style (QgsStyle)
working with color ramps (QgsColorRamp)
シンボルレイヤーとレンダラーのレジストリを調べる方法