Getting coordinates of Line or MultiLine using PyQGIS

Question

We can get point layer coordinates through the following code, but I want to know the coordinates of Line or MultiLine. How to get these coordinates?

layer = QgsProject.instance().mapLayersByName("layerName")[0]
features = layer.getFeatures()
for feature in features:
  geom = feature.geometry()
  print(geom.asPoint().x(), geom.asPoint().y())

Answer 1

For single part LineString:

layer = QgsProject.instance().mapLayersByName("Single parts")[0]
for feature in layer.getFeatures():
    for pnt in feature.geometry().asPolyline():
        print(pnt.x(), pnt.y())

For multipart LineString:

layer = QgsProject.instance().mapLayersByName("folyo")[0]
for feature in layer.getFeatures():
    for part in feature.geometry().asMultiPolyline():
        print("part")
        for pnt in part:
            print(pnt.x(), pnt.y())

Tested in QGIS 3.16.1

asMultiPolyline() and asPolyline() return a list of points, so you can use indexes.

To check the layer geometry type use the geometryType() method of a layer.

To separate single and multi types use the isSingleType() method.

Here is the code for it:

layer = QgsProject.instance().mapLayersByName("your_layer")[0]
if layer.geometryType() ==  QgsWkbTypes.LineGeometry:
for feature in layer.getFeatures():
    geom = feature.geometry()

    if QgsWkbTypes.isSingleType(geom.wkbType()):
        # single
        for pnt in geom.asPolyline():
            print(pnt.x(), pnt.y())
    else:
        # multipart
        for part in geom.asMultiPolyline():
            print("part")
            for pnt in part:
                print(pnt.x(), pnt.y())

Answer 2

If you want to extract the xy of vertices of a MultiPolyline geometry you can use the following code:

layer = QgsProject.instance().mapLayersByName("layerName")[0]
features = layer.getFeatures()
for feature in features:
    geom = feature.geometry()
    verts = geom.asMultiPolyline() # use geom.asPolyline() for line geometry
    for vert in verts:
        for i in range(len(vert)):
            print(vert[i].x(), vert[i].y())

The output will be like this:

-3487202.783144876 10010395.30478035
-3428476.505393841 10049595.900699263
-3428476.505393841 10049595.900699263
-3374593.995628879 9923727.261801671
-3428476.505393841 10049595.900699263
-3359626.0983730364 10059037.052994486