[GIS] How to determine bounding box of current qgis ‘map canvas extent’ from the python console

extentspythonqgisviewer

I've asked a similar question here: How to quickly calculate bounding box coordinates of a selected polygon with qgis

…regarding a quick way to determine the bounding box of a given layer.

Is there any way to do the same thing for the current qgis view? I imagine it is an iface property but cannot find it in the documentation. Thanks.

update:
I'm working with the qgis print (map) creator right now, and I've found a button which appears to call a function that I'm alluding to. If you open the print creator, in the right side bar there is a menu button called "Item Properties". Click on this and below there is a submenu called "Extents". Expand that and there is a button called "Set to map canvas extent". This button appears to utilize the function I'm alluding to by extracting the bbox coords of the main qgis map view.

Best Answer

This will return you the extent of the canvas.

extent = iface.mapCanvas().extent()

Reference: http://qgis.org/api/classQgsMapCanvas.html#a878f0c387c9475d59c6aac425db01020

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[GIS] Accurately find the bounding box of geography polygons

There's no quick and easy way but for the benefit of someone else with the same problem the solution is to convert the geography type to a geometry type, take the bounding box (envelope) of the geometry and pull out the 1st (min) and 3rd (max) points.

CGMinLong AS (CONVERT(float, geography::STGeomFromWKB( geometry::STGeomFromWKB(contactpolygon.STAsBinary(), contactpolygon.STSrid).STEnvelope().STAsBinary(), contactPolygon.STSrid).MakeValid().STPointN(1).Long)) PERSISTED,
CGMinLat AS (CONVERT(float,geography::STGeomFromWKB( geometry::STGeomFromWKB(contactpolygon.STAsBinary(), contactpolygon.STSrid).STEnvelope().STAsBinary(), contactPolygon.STSrid).MakeValid().STPointN(1).Lat)) PERSISTED,  
CGMaxLong AS (CONVERT(float,geography::STGeomFromWKB( geometry::STGeomFromWKB(contactpolygon.STAsBinary(), contactpolygon.STSrid).STEnvelope().STAsBinary(), contactPolygon.STSrid).MakeValid().STPointN(3).Long)) PERSISTED, 
CGMaxLat AS (CONVERT(float,geography::STGeomFromWKB( geometry::STGeomFromWKB(contactpolygon.STAsBinary(), contactpolygon.STSrid).STEnvelope().STAsBinary(), contactPolygon.STSrid).MakeValid().STPointN(3).Lat)) PERSISTED

Even with the conversions between types and WKB it still performs pretty well and if you use these min and max values instead of the spatial index (for retrieving shapes within a rectangle for display on the screen) you might find, like i have, that it performs more consistently and normally better than a spatial index search.

The search ends up looking like:

WHERE not(CGMaxLong < @minLon OR CGMinLong > @maxLon OR CGMaxLat < @minLat OR CGMinLat > @maxLat

where the @ parameters are your search area.

[GIS] How to refresh the view in QGIS Print Composer using Python

You're very close - you need to change:

sourceArea = QRectF(0, 0, c.paperWidth(), c.paperHeight())
targetArea = QRectF(0, 0, width, height)
c.render(imagePainter, targetArea, sourceArea)

c.renderPage( imagePainter, 0 )

As the renderPage method automatically handles a lot of output setup.

Best Answer

Related Solutions

[GIS] Accurately find the bounding box of geography polygons

[GIS] How to refresh the view in QGIS Print Composer using Python

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