Automating Print layout with export map canvas as image using PyQGIS

Question

I would like to automate two steps in my QGIS Print Layout by using PyQGIS

I have my print layout already created, and I was trying to open it by this code:

composerTitle = 'Strand3'
project = QgsProject.instance()
projectLayoutManager = project.layoutManager()
layout = projectLayoutManager.layoutByName(composerTitle)

which comes from this query:

How to select a specific print layout (by name) in QGIS 3?

The code didn't work as I wanted. I just wanted to load my print layout called "Strand3" from the layout manager. However is not as important as the stuff below, because I can load it once manually and keep it open.

Next, I would like to do an automatic Set Map Extent to Match Main Canvas Extent.

I found some solution here:

• Setting the extent for a QGIS map using python
• Set print composer to map canvas extent using python
• Map extent matching permanently main canvas extent

but it doesn't work, as they propose the definition of map rectangle. I simply need my map refreshed, what was considered here:

• QGIS print layout - map refresh not working

I would like to have this step done automatically as well as the last one - exporting map to PNG.

Since I've managed with setting the fixed DPI resolution for the map, I want to skip the window below:

when possible.

I found the code like this:

 .exportToImage(fn, QgsLayoutExporter.ImageExportSettings())
 exporter.exportToPdf(fn, QgsLayoutExporter.PdfExportSettings())

and solution like this:

• https://docs.qgis.org/testing/en/docs/pyqgis_developer_cookbook/composer.html#output-using-print-layout

but I don't know how to implement Qgis Layout Exporter.

Anyway my final code looks like this:

 comp = iface.createNewComposer()
 comp.composition().loadFromTemplate(myDocument)
map_item = comp.composition().getComposerItemById('Strand3')
 map_item.setMapCanvas(canvas)
 map_item.zoomToExtent(canvas.extent())
base_path = os.path.join(QgsProject.instance().homePath())
 png_path = os.path.join(base_path, ".png")
exporter = QgsLayoutExporter(layout)
 exporter.exportToPdf(png_path, QgsLayoutExporter.ImageExportSettings())

and I am getting an error: 'QgisInterface' object has no attribute 'createNewComposer'.

How can I automate these 2 things in my QGIS print layout?

Answer 1

As Kadir Şahbaz commented, you are mixing QGIS 2 & 3 APIs. A couple of other things:

-You don't need to actually open your layout, you just need a reference to the layout object.

-If you want to export a png you should use exportToImage() not exportToPdf().

Try the example below which is working for me.

project = QgsProject().instance()
canvas = iface.mapCanvas()
layout = project.layoutManager().layoutByName('Strand3')
map_item = [i for i in layout.items() if isinstance(i, QgsLayoutItemMap)][0]
map_item.zoomToExtent(canvas.extent())
fileName = QFileDialog.getSaveFileName(None, 'Save File', '', filter='*.png')
if fileName:
    png_path = fileName[0]
exporter = QgsLayoutExporter(layout)
settings = QgsLayoutExporter.ImageExportSettings()
#The idea is that here you can change setting attributes e.g.
#settings.cropToContents = True
#settings.dpi = 150
result = exporter.exportToImage(png_path, settings)
print(result)#0 = Export was successful!