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.
You can retrieve information about the fields associated with a vector layer by calling pendingFields() on a QgsVectorLayer instance:
# "layer" is a QgsVectorLayer instance
for field in layer.pendingFields():
print field.name(), field.typeName()
ノート
Starting from QGIS 2.12 there is also a fields() in QgsVectorLayer which is an alias to pendingFields().
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 can be useful to programmatically select features or to change the default color.
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 add features to the selected features list for a given layer, you can call setSelectedFeatures() passing to it the list of features IDs:
# Get the active layer (must be a vector layer)
layer = iface.activeLayer()
# Get the first feature from the layer
feature = layer.getFeatures().next()
# Add this features to the selected list
layer.setSelectedFeatures([feature.id()])
To clear the selection, just pass an empty list:
layer.setSelectedFeatures([])
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
iter = layer.getFeatures()
for feature in iter:
# retrieve every feature with its geometry and attributes
# fetch geometry
geom = feature.geometry()
print "Feature ID %d: " % feature.id()
# show some information about the feature
if geom.type() == QGis.Point:
x = geom.asPoint()
print "Point: " + str(x)
elif geom.type() == QGis.Line:
x = geom.asPolyline()
print "Line: %d points" % len(x)
elif geom.type() == QGis.Polygon:
x = geom.asPolygon()
numPts = 0
for ring in x:
numPts += len(ring)
print "Polygon: %d rings with %d points" % (len(x), numPts)
else:
print "Unknown"
# fetch attributes
attrs = feature.attributes()
# attrs is a list. It contains all the attribute values of this feature
print attrs
Attributes can be referred to by their name.
print feature['name']
Alternatively, attributes can be referred to by index. This is will be a bit faster than using the name. For example, to get the first attribute:
print feature[0]
if you only need selected features, you can use the selectedFeatures() method from vector layer:
selection = layer.selectedFeatures()
print len(selection)
for feature in selection:
# do whatever you need with the feature
Another option is the Processing features() method:
import processing
features = processing.features(layer)
for feature in features:
# do whatever you need with the feature
By default, this will iterate over all the features in the layer, in case there is no selection, or over the selected features otherwise. Note that this behavior can be changed in the Processing options to ignore selections.
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
request = QgsFeatureRequest()
request.setFilterRect(areaOfInterest)
for feature in layer.getFeatures(request):
# do whatever you need with the feature
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 an 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
request.setSubsetOfAttributes([0,2])
# More user friendly version
request.setSubsetOfAttributes(['name','id'],layer.pendingFields())
# Don't return geometry objects
request.setFlags(QgsFeatureRequest.NoGeometry)
ちなみに
Speed features request
If you only need a subset of the attributes or you don’t need the geometry information, you can significantly increase the speed of the features request by using QgsFeatureRequest.NoGeometry flag or specifying a subset of attributes (possibly empty) like shown in the example above.
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:
caps & QgsVectorDataProvider.DeleteFeatures
# Print 2 if DeleteFeatures is supported
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:
# u'Add Features, Delete Features, Change Attribute Values,
# Add Attributes, Delete Attributes, Create Spatial Index,
# Fast Access to Features at ID, Change Geometries,
# Simplify Geometries with topological validation'
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。
ノート
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.setCacheImage(None)
else:
iface.mapCanvas().refresh()
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 you can either initialize the feature passing a QgsFields instance or call initAttributes() passing the number of fields you want to be added.
if caps & QgsVectorDataProvider.AddFeatures:
feat = QgsFeature(layer.pendingFields())
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.fromPoint(QgsPoint(123, 456)))
(res, outFeats) = layer.dataProvider().addFeatures([feat])
To delete some features, just provide a list of their feature IDs
if caps & QgsVectorDataProvider.DeleteFeatures:
res = layer.dataProvider().deleteFeatures([5, 10])
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.fromPoint(QgsPoint(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 of useful methods to edit geometries (translate, insert or move vertex etc.).
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.
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 PyQt4.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()
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 do 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 committing changes, all changes from the editing buffer are saved to data provider.
To find out whether a layer is in editing mode, use isEditable() — the editing functions work only when the editing mode is turned on. Usage of editing functions
from PyQt4.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 given value (QVariant)
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.) How to 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() 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.
To start editing mode, there is startEditing() method, to stop editing there are commitChanges() and rollBack() — however normally you should not need these methods and leave this functionality to be triggered by the user.
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 = layer.getFeatures().next()
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.
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 — the following code creates an empty index
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 previous call to provider’s nextFeature()
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(QgsPoint(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))
You can write vector layer files using QgsVectorFileWriter class. It supports any other kind of vector file that OGR supports (shapefiles, GeoJSON, KML and others).
There are two possibilities how to export a vector layer:
from an instance of QgsVectorLayer
error = QgsVectorFileWriter.writeAsVectorFormat(layer, "my_shapes.shp", "CP1250", None, "ESRI Shapefile")
if error == QgsVectorFileWriter.NoError:
print "success!"
error = QgsVectorFileWriter.writeAsVectorFormat(layer, "my_json.json", "utf-8", None, "GeoJSON")
if error == QgsVectorFileWriter.NoError:
print "success again!"
The third parameter specifies output text encoding. Only some drivers need this for correct operation - shapefiles are one of those — however in case you are not using international characters you do not have to care much about the encoding. The fourth parameter that we left as None may specify destination CRS — if a valid instance of QgsCoordinateReferenceSystem is passed, the layer is transformed to that CRS.
有効なドライバ名は、 OGRでサポートされる形式 を調べて下さい — “Code” 列の表記をドライバ名として渡します。 選択された地物のみの出力や、作成のためのドライバ特有のオプション、属性を作成しないようにクラスに指示するといった指定をすることも出来ます — すべての構文については文書を見てください。
directly from features
from PyQt4.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", "CP1250", fields, QGis.WKBPoint, None, "ESRI Shapefile")
if writer.hasError() != QgsVectorFileWriter.NoError:
print "Error when creating shapefile: ", w.errorMessage()
# add a feature
fet = QgsFeature()
fet.setGeometry(QgsGeometry.fromPoint(QgsPoint(10,10)))
fet.setAttributes([1, "text"])
writer.addFeature(fet)
# delete the writer to flush features to disk
del writer
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.
コンストラクタはレイヤーのジオメトリの種類に指定したURLを与えることができます。この種類は次のものです: "Point", "LineString", "Polygon", "MultiPoint", "MultiLineString", "MultiPolygon" .
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、
プロバイダーが空間索引を使うことを指定します。
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 PyQt4.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.fromPoint(QgsPoint(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 = layer.extent()
print "extent:", e.xMiniminum(), e.yMinimum(), e.xMaximum(), e.yMaximum()
# iterate over features
f = QgsFeature()
features = vl.getFeatures()
for f in features:
print "F:", f.id(), f.attributes(), f.geometry().asPoint()
ベクターレイヤーがレンダリングされるとき、データの外観はレイヤーによって関連付けられた レンダラー と シンボル によって決定されます。シンボルは地物の仮想的な表現を描画するクラスで、レンダラーはシンボルが個々の地物で使われるかを決定します。
The renderer for a given layer can obtained as shown below:
renderer = layer.rendererV2()
この参照を利用して、少しだけ探索してみましょう:
print "Type:", rendererV2.type()
There are several known renderer types available in QGIS core library:
タイプ |
クラス |
詳細 |
|---|---|---|
単一シンボル |
QgsSingleSymbolRendererV2 | 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 |
QgsCategorizedSymbolRendererV2 | 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 |
QgsGraduatedSymbolRendererV2 | 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 QgsRendererV2Registry singleton to find out currently available renderers:
print QgsRendererV2Registry.instance().renderersList()
# Print:
[u'singleSymbol',
u'categorizedSymbol',
u'graduatedSymbol',
u'RuleRenderer',
u'pointDisplacement',
u'invertedPolygonRenderer',
u'heatmapRenderer']
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 rendererV2.dump()
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 QgsMarkerSymbolV2, QgsLineSymbolV2 and QgsFillSymbolV2.
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 QgsMarkerSymbolV2 as in the following code example:
symbol = QgsMarkerSymbolV2.createSimple({'name': 'square', 'color': 'red'})
layer.rendererV2().setSymbol(symbol)
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。
To get the full list of properties for the first symbol layer of a simbol instance you can follow the example code:
print layer.rendererV2().symbol().symbolLayers()[0].properties()
# Prints
{u'angle': u'0',
u'color': u'0,128,0,255',
u'horizontal_anchor_point': u'1',
u'name': u'circle',
u'offset': u'0,0',
u'offset_map_unit_scale': u'0,0',
u'offset_unit': u'MM',
u'outline_color': u'0,0,0,255',
u'outline_style': u'solid',
u'outline_width': u'0',
u'outline_width_map_unit_scale': u'0,0',
u'outline_width_unit': u'MM',
u'scale_method': u'area',
u'size': u'2',
u'size_map_unit_scale': u'0,0',
u'size_unit': u'MM',
u'vertical_anchor_point': u'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.rendererV2().symbol().symbolLayer(0).setName('square')
# ... but not all properties are accessible from methods,
# you can also replace the symbol completely:
props = layer.rendererV2().symbol().symbolLayer(0).properties()
props['color'] = 'yellow'
props['name'] = 'square'
layer.rendererV2().setSymbol(QgsMarkerSymbolV2.createSimple(props))
You can query and set attribute name which is used for classification: use classAttribute() and setClassAttribute() methods.
カテゴリの配列を取得するには
for cat in rendererV2.categories():
print "%s: %s :: %s" % (cat.value().toString(), cat.label(), str(cat.symbol()))
Where value() is the value used for discrimination between categories, label() is a text used for category description and symbol() method returns assigned symbol.
The renderer usually stores also original symbol and color ramp which were used for the classification: sourceColorRamp() and sourceSymbol() methods.
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 rendererV2.ranges():
print "%f - %f: %s %s" % (
ran.lowerValue(),
ran.upperValue(),
ran.label(),
str(ran.symbol())
)
ここでも属性名の分類を調べるために classAttribute() 、 sourceSymbol() 、 sourceColorRamp() メソッドを使用できます。さらに、等間隔、分位数、または他の方法を使用して、範囲の作成方法を決定する mode() メソッドもあります。
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.core import *
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 = QgsSymbolV2.defaultSymbol(myVectorLayer.geometryType())
mySymbol1.setColor(myColour)
mySymbol1.setAlpha(myOpacity)
myRange1 = QgsRendererRangeV2(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 = QgsSymbolV2.defaultSymbol(
myVectorLayer.geometryType())
mySymbol2.setColor(myColour)
mySymbol2.setAlpha(myOpacity)
myRange2 = QgsRendererRangeV2(myMin, myMax, mySymbol2 myLabel)
myRangeList.append(myRange2)
myRenderer = QgsGraduatedSymbolRendererV2('', myRangeList)
myRenderer.setMode(QgsGraduatedSymbolRendererV2.EqualInterval)
myRenderer.setClassAttribute(myTargetField)
myVectorLayer.setRendererV2(myRenderer)
QgsMapLayerRegistry.instance().addMapLayer(myVectorLayer)
For representation of symbols, there is QgsSymbolV2 base class with three derived classes:
Every symbol consists of one or more symbol layers (classes derived from QgsSymbolLayerV2). 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: 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 xrange(symbol.symbolLayerCount()):
lyr = symbol.symbolLayer(i)
print "%d: %s" % (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 size() and angle() methods, for line symbols there is width() method returning 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。
As said before, symbol layers (subclasses of QgsSymbolLayerV2) 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 like this
from qgis.core import QgsSymbolLayerV2Registry
myRegistry = QgsSymbolLayerV2Registry.instance()
myMetadata = myRegistry.symbolLayerMetadata("SimpleFill")
for item in myRegistry.symbolLayersForType(QgsSymbolV2.Marker):
print item
Output
EllipseMarker
FontMarker
SimpleMarker
SvgMarker
VectorField
QgsSymbolLayerV2Registry 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 generic methods color(), size(), angle(), width() with their setter counterparts. Of course size and angle is available only for marker symbol layers and width for line symbol layers.
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:
class FooSymbolLayer(QgsMarkerSymbolLayerV2):
def __init__(self, radius=4.0):
QgsMarkerSymbolLayerV2.__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. Properties are used for persistence of attributes. 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 first feature, stopRender() when rendering is done. And renderPoint() method which does 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, resp. renderPolygon() which receives list of points on outer ring as a 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:
class FooSymbolLayerWidget(QgsSymbolLayerV2Widget):
def __init__(self, parent=None):
QgsSymbolLayerV2Widget.__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()"))
このウィジェットはシンボルプロパティのダイアログに組み込むことができます。シンボルプロパティのダイアログでシンボルレイヤータイプを選択したとき、これはシンボルレイヤーのインスタンスとシンボルレイヤーウィジェットのインスタンスを作成します。そしてそのウィジェットにシンボルレイヤーを割り当てるために setSymbolLayer() メソッドを呼び出します。そのメソッド中ではウィジェットはシンボルレイヤーの属性を反映するようUIを更新します。 symbolLayer() 関数はシンボルが使ってるプロパティダイアログがシンボルレイヤーを再度探すのに使われます。
いかなる属性の変更時でも、プロパティダイアログにシンボルプレビューを更新させるために ウィジェットは changed() シグナルを発生します。
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
class FooSymbolLayerMetadata(QgsSymbolLayerV2AbstractMetadata):
def __init__(self):
QgsSymbolLayerV2AbstractMetadata.__init__(self, "FooMarker", QgsSymbolV2.Marker)
def createSymbolLayer(self, props):
radius = float(props[QString("radius")]) if QString("radius") in props else 4.0
return FooSymbolLayer(radius)
def createSymbolLayerWidget(self):
return FooSymbolLayerWidget()
QgsSymbolLayerV2Registry.instance().addSymbolLayerType(FooSymbolLayerMetadata())
You should pass layer type (the same as returned by the layer) and symbol type (marker/line/fill) to the constructor of parent class. createSymbolLayer() takes care of creating an instance of symbol layer with attributes specified in the props dictionary. (Beware, the keys are QString instances, not “str” objects). And there is createSymbolLayerWidget() method which returns 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。
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
class RandomRenderer(QgsFeatureRendererV2):
def __init__(self, syms=None):
QgsFeatureRendererV2.__init__(self, "RandomRenderer")
self.syms = syms if syms else [QgsSymbolV2.defaultSymbol(QGis.Point), QgsSymbolV2.defaultSymbol(QGis.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)
The constructor of parent QgsFeatureRendererV2 class needs renderer name (has to be unique among renderers). 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. usedAttributes() method can return a list of field names that renderer expects to be present. Finally clone() function 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 QgsRendererV2Widget. The following sample code creates a button that allows user to set symbol of the first symbol
class RandomRendererWidget(QgsRendererV2Widget):
def __init__(self, layer, style, renderer):
QgsRendererV2Widget.__init__(self, layer, style)
if renderer is None or renderer.type() != "RandomRenderer":
self.r = RandomRenderer()
else:
self.r = renderer
# setup UI
self.btn1 = QgsColorButtonV2()
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 (QgsStyleV2) and 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, 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
class RandomRendererMetadata(QgsRendererV2AbstractMetadata):
def __init__(self):
QgsRendererV2AbstractMetadata.__init__(self, "RandomRenderer", "Random renderer")
def createRenderer(self, element):
return RandomRenderer()
def createRendererWidget(self, layer, style, renderer):
return RandomRendererWidget(layer, style, renderer)
QgsRendererV2Registry.instance().addRenderer(RandomRendererMetadata())
抽象メタデータコンストラクタは、シンボルレイヤーと同様に、レンダラー名、ユーザーに表示される名前、およびオプションでレンダラーのアイコンの名前を待っています。 createRenderer() メソッドは、DOMツリーからレンダラーの状態を復元するために使用できるクラス QDomElement インスタンスを渡します。 createRendererWidget() メソッドは設定ウィジェットを作成します。レンダラーにGUIが付属していない場合は、存在する必要はなく、 None を返すことができます。
To associate an icon with the renderer you can assign it in QgsRendererV2AbstractMetadata constructor as a third (optional) argument — the base class constructor in the RandomRendererMetadata __init__() function becomes
QgsRendererV2AbstractMetadata.__init__(self,
"RandomRenderer",
"Random renderer",
QIcon(QPixmap("RandomRendererIcon.png", "png")))
The icon can be associated also at any later time using 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 (PyQt4 includes .qrc compiler for Python).
TODO:
シンボルの作成や修正
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