レイヤのロード¶

ベクタレイヤ¶

To load a vector layer, specify layer’s data source identifier, name for the layer and provider’s name:

layer = QgsVectorLayer(data_source, layer_name, provider_name)
if not layer.isValid():
  print "Layer failed to load!"

データソース識別子は文字列でそれぞれのデータプロバイダを表します.レイヤ名はレイヤリストウィジェットで使われます.レイヤが正常にロードされたかどうかをチェックすることは重要です.正しくロードされていない場合は不正なレイヤインスタンスが返ります.

The quickest way to open and display a vector layer in QGIS is the addVectorLayer function of the QgisInterface:

layer = iface.addVectorLayer("/path/to/shapefile/file.shp", "layer_name_you_like", "ogr")
if not layer:
  print "Layer failed to load!"

This creates a new layer and adds it to the map layer registry (making it appear in the layer list) in one step. The function returns the layer instance or None if the layer couldn’t be loaded.

以下のリストはベクタデータプロバイダを使って様々なデータソースにアクセスする方法が記述されています.

• OGR library (shapefiles and many other file formats) — data source is the path to the file

  vlayer = QgsVectorLayer("/path/to/shapefile/file.shp", "layer_name_you_like", "ogr")
  

• PostGIS database — data source is a string with all information needed to create a connection to PostgreSQL database. QgsDataSourceURI class can generate this string for you. Note that QGIS has to be compiled with Postgres support, otherwise this provider isn’t available.

  uri = QgsDataSourceURI()
  # set host name, port, database name, username and password
  uri.setConnection("localhost", "5432", "dbname", "johny", "xxx")
  # set database schema, table name, geometry column and optionally
  # subset (WHERE clause)
  uri.setDataSource("public", "roads", "the_geom", "cityid = 2643")
  
  vlayer = QgsVectorLayer(uri.uri(), "layer_name_you_like", "postgres")
  

• CSV or other delimited text files — to open a file with a semicolon as a delimiter, with field “x” for x-coordinate and field “y” with y-coordinate you would use something like this

  uri = "/some/path/file.csv?delimiter=%s&xField=%s&yField=%s" % (";", "x", "y")
  vlayer = QgsVectorLayer(uri, "layer_name_you_like", "delimitedtext")
  

  Note: from QGIS version 1.7 the provider string is structured as a URL, so the path must be prefixed with file://. Also it allows WKT (well known text) formatted geometries as an alternative to “x” and “y” fields, and allows the coordinate reference system to be specified. For example

  uri = "file:///some/path/file.csv?delimiter=%s&crs=epsg:4723&wktField=%s" % (";", "shape")
  

• GPX files — the “gpx” data provider reads tracks, routes and waypoints from gpx files. To open a file, the type (track/route/waypoint) needs to be specified as part of the url

  uri = "path/to/gpx/file.gpx?type=track"
  vlayer = QgsVectorLayer(uri, "layer_name_you_like", "gpx")
  

• SpatiaLite database — supported from QGIS v1.1. Similarly to PostGIS databases, QgsDataSourceURI can be used for generation of data source identifier

  uri = QgsDataSourceURI()
  uri.setDatabase('/home/martin/test-2.3.sqlite')
  schema = ''
  table = 'Towns'
  geom_column = 'Geometry'
  uri.setDataSource(schema, table, geom_column)
  
  display_name = 'Towns'
  vlayer = QgsVectorLayer(uri.uri(), display_name, 'spatialite')
  

• MySQL WKB-based geometries, through OGR — data source is the connection string to the table

  uri = "MySQL:dbname,host=localhost,port=3306,user=root,password=xxx|layername=my_table"
  vlayer = QgsVectorLayer( uri, "my_table", "ogr" )
  

• WFS connection:. the connection is defined with a URI and using the WFS provider

  uri = "http://localhost:8080/geoserver/wfs?srsname=EPSG:23030&typename=union&version=1.0.0&request=GetFeature&service=WFS",
  vlayer = QgsVectorLayer("my_wfs_layer", "WFS")
  

  The uri can be created using the standard urllib library.

  params = {
      'service': 'WFS',
      'version': '1.0.0',
      'request': 'GetFeature',
      'typename': 'union',
      'srsname': "EPSG:23030"
  }
  uri = 'http://localhost:8080/geoserver/wfs?' + urllib.unquote(urllib.urlencode(params))
  

ラスタレイヤ¶

For accessing raster files, GDAL library is used. It supports a wide range of file formats. In case you have troubles with opening some files, check whether your GDAL has support for the particular format (not all formats are available by default). To load a raster from a file, specify its file name and base name

fileName = "/path/to/raster/file.tif"
fileInfo = QFileInfo(fileName)
baseName = fileInfo.baseName()
rlayer = QgsRasterLayer(fileName, baseName)
if not rlayer.isValid():
  print "Layer failed to load!"

Similarly to vector layers, raster layers can be loaded using the addRasterLayer function of the QgisInterface:

iface.addRasterLayer("/path/to/raster/file.tif", "layer_name_you_like")

This creates a new layer and adds it to the map layer registry (making it appear in the layer list) in one step.

Raster layers can also be created from a WCS service.

layer_name = 'modis'
uri = QgsDataSourceURI()
uri.setParam('url', 'http://demo.mapserver.org/cgi-bin/wcs')
uri.setParam("identifier", layer_name)
rlayer = QgsRasterLayer(str(uri.encodedUri()), 'my_wcs_layer', 'wcs')

detailed URI settings can be found in provider documentation

Alternatively you can load a raster layer from WMS server. However currently it’s not possible to access GetCapabilities response from API — you have to know what layers you want

urlWithParams = 'url=http://wms.jpl.nasa.gov/wms.cgi&layers=global_mosaic&styles=pseudo&format=image/jpeg&crs=EPSG:4326'
rlayer = QgsRasterLayer(urlWithParams, 'some layer name', 'wms')
if not rlayer.isValid():
  print "Layer failed to load!"

マップレイヤレジストリ¶

もしあなたが開かれているレイヤを描画に利用したい場合はそれらをマップレイヤレジストリに追加することを忘れないで下さい.マップレイヤレジストリはレイヤのオーナーシップを取得して後でアプリケーションのいろいろな場所でユニークIDを使ってアクセスできるようになります.レイヤがマップレイヤレジストリから削除された削除された時にそれも削除されます.

Adding a layer to the registry

QgsMapLayerRegistry.instance().addMapLayer(layer)

Layers are destroyed automatically on exit, however if you want to delete the layer explicitly, use

QgsMapLayerRegistry.instance().removeMapLayer(layer_id)

For a list of loaded layers and layer ids, use

QgsMapLayerRegistry.instance().mapLayers()

TODO:

More about map layer registry?