[QGIS-Developer] QgsPrintLayout Setup from PyQGIS 3

[Nyall Dawson]

On 27 March 2018 at 23:55, Brian Libgober <libgober at gmail.com> wrote:
> I am interested in making reproducible PDF figures in QGIS3, and therefore
> want to work from the console/PyQGIS. Thanks to some previous helpful advice
> here, the problem is successfully reduced to setting up the QgsPrintLayout.
> I am not sure how to do this, below is my best attempt so far:
>
> #setup the background classes for managing the project
> canvas =iface.mapCanvas()
> manager = project.layoutManager()
> #new layout
> layout = QgsPrintLayout(project)
> layout.initializeDefaults()
> layout.setName('console')
> itemMap = QgsLayoutItemMap(layout)
> itemMap.setExtent(canvas.extent())
> layout.addLayoutItem(itemMap)
> #add the layout to the manager
> manager.addLayout(layout)
>
> The "console" layout is successfully added to QGIS 3 and I can open it to
> see if the content is satisfactory. The map does not render and its extent
> is nan,nan,nan,nan. How do I setup the extent and size of the map object in
> the layout?
>

I answered over on stackexchange too, but for completeness:

You need to set a size for the map item (usually you do this before
setting the extent):

itemMap.attemptResize(QgsLayoutSize(50, 60, QgsUnitTypes.LayoutMillimeters))
itemMap.attemptMove(QgsLayoutPoint(1,2,QgsUnitTypes.LayoutMillimeters))
itemMap.setExtent(...)

This is because the call to setExtent uses the item size for various
scale and aspect ratio calculations, and initially a new item is
created with an empty size.

Nyall