Getting QgsMapCanvas viewport's four corners' coordinates

Question

I have a PyQGIS application that uses the QgsMapCanvas as map display. I am trying to retrieve its four corners' coordinates, but couldn't find any public function to do that. All I have is its width() and height().

Is there any way to get the actual coordinates of the corners of the viewport?

Let me provide further context, I need the map canvas's viewport's corners' coordinates when it has not had any layers loaded into it yet or the first layer I am constructing is in memory that has yet to set its projection, I found that in such cases, the map canvas's extent is empty, so calling its extent won't help.

Answer 1

Would extent() work?

canvas = iface.mapCanvas()
extent = canvas.extent()
print(extent)

Taking it one step further you can break the QgsRectangle object into its components:

xmax = extent.xMaximum()
ymax = extent.yMaximum()
xmin = extent.xMinimum()
ymin = extent.yMinimum()

Answer 2

QgsMapCanvas is just a subclass of the Graphics View Framework's QGraphicsView class. The documentation for QgsMapCanvas doesn't list the base class members, so you need to consult the Graphics View Framework documentation.

For example: https://www.riverbankcomputing.com/static/Docs/PyQt4/qgraphicsview.html

The sceneRect() method is probably what you want. It gives you the rectangle of the QGraphicsView (or QgsMapCanvas) object, relative to the underlying QGraphicsScene. The rectangle is returned as a QRectF object.

So, if myMapCanvas holds your QgsMapCanvas object ...

 myCanvasRect = myMapCanvas.sceneRect()

QRectF has methods like x(), y(), width(), height(), left(), right(), top() and bottom() that return float values.

It also has convenience methods, like center(), topLeft(), bottomRight() etc. that return QPointF objects.

Don't confuse the sceneRect() and extent() methods. The former returns a rectangle in scene space. The latter returns a rectangle in map space.