10. 地図のレンダリングと印刷

ヒント

The code snippets on this page need the following imports:

 1import os
 2
 3from qgis.core import (
 4    QgsGeometry,
 5    QgsMapSettings,
 6    QgsPrintLayout,
 7    QgsMapSettings,
 8    QgsMapRendererParallelJob,
 9    QgsLayoutItemLabel,
10    QgsLayoutItemLegend,
11    QgsLayoutItemMap,
12    QgsLayoutItemPolygon,
13    QgsLayoutItemScaleBar,
14    QgsLayoutExporter,
15    QgsLayoutItem,
16    QgsLayoutPoint,
17    QgsLayoutSize,
18    QgsUnitTypes,
19    QgsProject,
20    QgsFillSymbol,
21)
22
23from qgis.PyQt.QtGui import (
24    QPolygonF,
25    QColor,
26)
27
28from qgis.PyQt.QtCore import (
29    QPointF,
30    QRectF,
31    QSize,
32)

入力データを地図として描画せねばならないときには、総じてふたつのアプローチがあります。 QgsMapRendererJob を使って手早く済ませるか、もしくは :class:`QgsLayout ` クラスで地図を構成し、より精密に調整された出力を作成するかです。

10.1. 単純なレンダリング

The rendering is done creating a QgsMapSettings object to define the rendering settings, and then constructing a QgsMapRendererJob with those settings. The latter is then used to create the resulting image.

こちらがサンプルです。

 1image_location = os.path.join(QgsProject.instance().homePath(), "render.png")
 2
 3vlayer = iface.activeLayer()
 4settings = QgsMapSettings()
 5settings.setLayers([vlayer])
 6settings.setBackgroundColor(QColor(255, 255, 255))
 7settings.setOutputSize(QSize(800, 600))
 8settings.setExtent(vlayer.extent())
 9
10render = QgsMapRendererParallelJob(settings)
11
12def finished():
13    img = render.renderedImage()
14    # save the image; e.g. img.save("/Users/myuser/render.png","png")
15    img.save(image_location, "png")
16
17render.finished.connect(finished)
18
19# Start the rendering
20render.start()
21
22# The following loop is not normally required, we
23# are using it here because this is a standalone example.
24from qgis.PyQt.QtCore import QEventLoop
25loop = QEventLoop()
26render.finished.connect(loop.quit)
27loop.exec_()

10.2. 異なるCRSを持つレイヤーをレンダリングする

レイヤが複数あり、それぞれのCRSが異なっている場合は、上記の単純な例ではおそらく求める結果は得られません。範囲計算から正しい値を得るためには、明示的に目的のCRSを設定する必要があります。

layers = [iface.activeLayer()]
settings = QgsMapSettings()
settings.setLayers(layers)
settings.setDestinationCrs(layers[0].crs())

10.3. 印刷レイアウトを使用して出力する

Print layout is a very handy tool if you would like to do a more sophisticated output than the simple rendering shown above. It is possible to create complex map layouts consisting of map views, labels, legend, tables and other elements that are usually present on paper maps. The layouts can be then exported to PDF, raster images or directly printed on a printer.

The layout consists of a bunch of classes. They all belong to the core library. QGIS application has a convenient GUI for placement of the elements, though it is not available in the GUI library. If you are not familiar with Qt Graphics View framework, then you are encouraged to check the documentation now, because the layout is based on it.

The central class of the layout is the QgsLayout class, which is derived from the Qt QGraphicsScene class. Let us create an instance of it:

project = QgsProject.instance()
layout = QgsPrintLayout(project)
layout.initializeDefaults()

This initializes the layout with some default settings, specifically by adding an empty A4 page to the layout. You can create layouts without calling the initializeDefaults() method, but you'll need to take care of adding pages to the layout yourself.

The previous code creates a "temporary" layout that is not visible in the GUI. It can be handy to e.g. quickly add some items and export without modifying the project itself nor expose these changes to the user. If you want the layout to be saved/restored along with the project and available in the layout manager, then add:

layout.setName("MyLayout")
project.layoutManager().addLayout(layout)

Now we can add various elements (map, label, ...) to the layout. All these objects are represented by classes that inherit from the base QgsLayoutItem class.

Here's a description of some of the main layout items that can be added to a layout.

  • map --- Here we create a map of a custom size and render the current map canvas

    1map = QgsLayoutItemMap(layout)
2# Set map item position and size (by default, it is a 0 width/0 height item placed at 0,0)
3map.attemptMove(QgsLayoutPoint(5,5, QgsUnitTypes.LayoutMillimeters))
4map.attemptResize(QgsLayoutSize(200,200, QgsUnitTypes.LayoutMillimeters))
5# Provide an extent to render
6map.zoomToExtent(iface.mapCanvas().extent())
7layout.addLayoutItem(map)

  • label --- ラベルを表示できます。そのフォント、色、配置及びマージンを変更することが可能です

    label = QgsLayoutItemLabel(layout)
label.setText("Hello world")
label.adjustSizeToText()
layout.addLayoutItem(label)

  • 凡例

    legend = QgsLayoutItemLegend(layout)
legend.setLinkedMap(map) # map is an instance of QgsLayoutItemMap
layout.addLayoutItem(legend)

  • スケールバー

    1item = QgsLayoutItemScaleBar(layout)
2item.setStyle('Numeric') # optionally modify the style
3item.setLinkedMap(map) # map is an instance of QgsLayoutItemMap
4item.applyDefaultSize()
5layout.addLayoutItem(item)

  • 矢印

  • picture

  • 基本図形

  • ノードに基づく図形

     1polygon = QPolygonF()
 2polygon.append(QPointF(0.0, 0.0))
 3polygon.append(QPointF(100.0, 0.0))
 4polygon.append(QPointF(200.0, 100.0))
 5polygon.append(QPointF(100.0, 200.0))
 6
 7polygonItem = QgsLayoutItemPolygon(polygon, layout)
 8layout.addLayoutItem(polygonItem)
 9
10props = {}
11props["color"] = "green"
12props["style"] = "solid"
13props["style_border"] = "solid"
14props["color_border"] = "black"
15props["width_border"] = "10.0"
16props["joinstyle"] = "miter"
17
18symbol = QgsFillSymbol.createSimple(props)
19polygonItem.setSymbol(symbol)

  • 表

Once an item is added to the layout, it can be moved and resized:

item.attemptMove(QgsLayoutPoint(1.4, 1.8, QgsUnitTypes.LayoutCentimeters))
item.attemptResize(QgsLayoutSize(2.8, 2.2, QgsUnitTypes.LayoutCentimeters))

A frame is drawn around each item by default. You can remove it as follows:

# for a composer label
label.setFrameEnabled(False)

Besides creating the layout items by hand, QGIS has support for layout templates which are essentially compositions with all their items saved to a .qpt file (with XML syntax).

Once the composition is ready (the layout items have been created and added to the composition), we can proceed to produce a raster and/or vector output.

10.3.1. Exporting the layout

To export a layout, the QgsLayoutExporter class must be used.

1base_path = os.path.join(QgsProject.instance().homePath())
2pdf_path = os.path.join(base_path, "output.pdf")
3
4exporter = QgsLayoutExporter(layout)
5exporter.exportToPdf(pdf_path, QgsLayoutExporter.PdfExportSettings())

Use the exportToImage() in case you want to export to an image instead of a PDF file.

10.3.2. Exporting a layout atlas

If you want to export all pages from a layout that has the atlas option configured and enabled, you need to use the atlas() method in the exporter (QgsLayoutExporter) with small adjustments. In the following example, the pages are exported to PNG images:

exporter.exportToImage(layout.atlas(), base_path, 'png', QgsLayoutExporter.ImageExportSettings())

Notice that the outputs will be saved in the base path folder, using the output filename expression configured on atlas.