pyqgisqgis
I'd like to change the value of a user-defined project variable (can be manually edited in Project Settings | Variables) using the Python console. I tracked down the setVariable() function in the QgsExpressionContextScope class but haven't succeeded in actually changing the variable in the project settings. My code so far:
iface.mapCanvas().mapSettings().expressionContext().scope(0).setVariable('myvar',1)
I guess I'm getting lost in the different expression contexts …
You need to use QgsCoordinateReferenceSystem and QgsCoordinateTransform classes. I tried out next code to transform polygon vector layer of next image from EPSG: 32612 to EPSG: 4326.
layer = iface.activeLayer()
crsSrc = QgsCoordinateReferenceSystem(32612)
crsDest = QgsCoordinateReferenceSystem(4326)
xform = QgsCoordinateTransform(crsSrc, crsDest)
feats = [ feat for feat in layer.getFeatures() ]
poly = feats[0].geometry().asPolygon()
poly_reproj = poly
for i, point in enumerate(poly[0]):
pt = xform.transform(point)
poly_reproj[0][i] = pt
print pt
mem_layer = QgsVectorLayer("Polygon?crs=epsg:4326&field=id:integer&index=yes",
"layer_memory",
"memory")
QgsMapLayerRegistry.instance().addMapLayer(mem_layer)
prov = mem_layer.dataProvider()
feature = QgsFeature()
feature.setGeometry(QgsGeometry.fromPolygon(poly_reproj))
#set attributes values
feature.setAttributes([1])
prov.addFeatures([feature])
After running the code, reprojected layer was adequately produced as a memory layer.
Best Answer
Look at QgsExpressionContextUtils (https://qgis.org/api/classQgsExpressionContextUtils.html). The method you need is QgsExpressionContextUtils.setProjectVariable, e.g.