The code snippets on this page need the following imports:

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import os

from qgis.core import (
    QgsGeometry,
    QgsMapSettings,
    QgsPrintLayout,
    QgsMapSettings,
    QgsMapRendererParallelJob,
    QgsLayoutItemLabel,
    QgsLayoutItemLegend,
    QgsLayoutItemMap,
    QgsLayoutItemPolygon,
    QgsLayoutItemScaleBar,
    QgsLayoutExporter,
    QgsLayoutItem,
    QgsLayoutPoint,
    QgsLayoutSize,
    QgsUnitTypes,
    QgsProject,
    QgsFillSymbol,
)

from qgis.PyQt.QtGui import (
    QPolygonF,
    QColor,
)

from qgis.PyQt.QtCore import (
    QPointF,
    QRectF,
    QSize,
)

10. 地図のレンダリングと印刷

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。

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image_location = os.path.join(QgsProject.instance().homePath(), "render.png")

vlayer = iface.activeLayer()
settings = QgsMapSettings()
settings.setLayers([vlayer])
settings.setBackgroundColor(QColor(255, 255, 255))
settings.setOutputSize(QSize(800, 600))
settings.setExtent(vlayer.extent())

render = QgsMapRendererParallelJob(settings)

def finished():
    img = render.renderedImage()
    # save the image; e.g. img.save("/Users/myuser/render.png","png")
    img.save(image_location, "png")

render.finished.connect(finished)

render.start()

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

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 --- このアイテムは地図自体を置くためのライブラリを伝えます。ここでは、地図を作成し、全体の用紙サイズの上に伸ばします

    map = QgsLayoutItemMap(layout)
layout.addItem(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.addItem(label)

  • 凡例

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

  • スケールバー

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    item = QgsLayoutItemScaleBar(layout)
item.setStyle('Numeric') # optionally modify the style
item.setLinkedMap(map) # map is an instance of QgsLayoutItemMap
item.applyDefaultSize()
layout.addItem(item)

  • 矢印

  • picture

  • 基本図形

  • ノードに基づく図形

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    polygon = QPolygonF()
polygon.append(QPointF(0.0, 0.0))
polygon.append(QPointF(100.0, 0.0))
polygon.append(QPointF(200.0, 100.0))
polygon.append(QPointF(100.0, 200.0))

polygonItem = QgsLayoutItemPolygon(polygon, layout)
layout.addItem(polygonItem)

props = {}
props["color"] = "green"
props["style"] = "solid"
props["style_border"] = "solid"
props["color_border"] = "black"
props["width_border"] = "10.0"
props["joinstyle"] = "miter"

symbol = QgsFillSymbol.createSimple(props)
polygonItem.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.

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base_path = os.path.join(QgsProject.instance().homePath())
pdf_path = os.path.join(base_path, "output.pdf")

exporter = QgsLayoutExporter(layout)
exporter.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.