Reprojecting layer using PyQGIS

Question

I'm trying to find a very simple solution to reproject a vector layer into a temporary layer in PyQGIS, however documentation is really extensive and I'm fairly new to PyQGIS; the only answer I've found here saves the layer, which I totally want to avoid.

The code I've tried:

layer = QgsVectorLayer("/path/file.gpkg", "oko", "ogr")
epsg_crs = QgsCoordinateReferenceSystem(4326, QgsCoordinateReferenceSystem.EpsgCrsId)
layer.setCoordinateSystem(epsg_crs)

And this error I got:

Traceback (most recent call last):
  File "/usr/lib/python3.6/code.py", line 91, in runcode
    exec(code, self.locals)
  File "<input>", line 1, in <module>
TypeError: QgsVectorLayer.setCoordinateSystem(): too many arguments

The answer you mentioned writes the input to a new output, because this way coordinates are changed/transformed to the new projection, while using setCoordinateSystem() just change the definition of the CRS and leaves the geometry as it is. So the idea to write a new output layer is correct, you can do that with a memory layer if you want. — Andreas Müller, Mar 20 '19 at 10:01

score 16 · Accepted Answer · edited Dec 19 '22 at 11:59

16

You can use processing algorithm native:reprojectlayer.

Example:

lyr = iface.activeLayer()
parameter = {
    'INPUT': lyr,
    'TARGET_CRS': 'EPSG:4326',
    'OUTPUT': 'memory:Reprojected'
}
result = processing.run('native:reprojectlayer', parameter)['OUTPUT']
QgsProject.instance().addMapLayer(result)

edited Dec 19 '22 at 11:59

Taras

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answered Mar 22 '19 at 10:42

Fran Raga

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score 5 · Answer 2 · edited Dec 19 '22 at 12:00

If you do not want to use Processing Tools you can do it like:

layer = iface.activeLayer()
source_crs = QgsCoordinateReferenceSystem(layer.crs().authid())
target_crs = QgsCoordinateReferenceSystem("EPSG:4326")
with edit(layer):
    for feat in layer.getFeatures():
        # you need to store the geometry in a variable to reproject it; you can not reproject without doing so
        geom = feat.geometry() 
        # transform the geometry
        geom.transform(QgsCoordinateTransform(source_crs, target_crs, QgsProject.instance()))
        # now update the features geometry
        feat.setGeometry(geom)
        # dont forget to update the feature, otherwise the changes will have no effect
        layer.updateFeature(feat)
    # finally simply set the layers crs to the new one
    layer.setCrs(target_crs)

Also see: https://qgis.org/pyqgis/3.16/core/QgsGeometry.html#qgis.core.QgsGeometry.transform

Reprojecting layer using PyQGIS

2 Answers2

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