Getting attribute values from vector features visible in QGIS canvas using PyQGIS

Question

I have a vector layer (grid). Currently I select some tiles with the select tool and paste some Python code to get information about these features.

layer = qgis.utils.iface.activeLayer()
selected_features = layer.selectedFeatures()
for i in selected_features:
 ...

Now, I want to get the feature values from the tiles which I can see on the map canvas, without selecting them.

There were two possibilities.

1. Selecting only the features which are fully visible ("contained" in the map canvas)
2. Selecting all features which are also partly visible ("intersecting" the map canvas)

Is there a way to do this with PyQGIS?

Answer 1

Yes, it is possible by using a QgsFeatureRequest with 'setFilterRect' method. The argument of this method is a QgsRectangle object obtained for visible part of Map Canvas with its 'extent' method (QgsMapCanvas class). I tried out my approach with this code:

layer = iface.activeLayer()
mapcanvas = iface.mapCanvas()
rect = mapcanvas.extent()
request = QgsFeatureRequest().setFilterRect(rect)
selected_feats = layer.getFeatures(request)
attr = [ feat.attributes() for feat in selected_feats ]
print attr
print len(attr)

and world_borders shapefile that has 3784 features. After running the code with the next image situation:

enter image description here

I got the display of only 77 visible features attributes (printed result at the Python Console of GIS).