[GIS] Get the Z values of existing lineStringZ with PyQGIS

geometrypolyline-creationpyqgis-3qgis-plugins

I can get the values of 3D QgsPoints with mypoint.get().z() When I iterate through a layer to get a specific polyline and then iterate through the polyline to get the start and end points- start_point = QgsPoint(geom[0]) I get a QgsPointXY and no Z values. They are there until the iteration geom[0] and then poof gone.

Is there a way to include the z values with something other than QgsPoint(geom[-1])?

My related question is Changing the coordinate value of a Pointz object with python – which is actually how I got the points to create the polyLine

I am taking this route next
Adding Z value from a Point field to a LineString using pyqgis

Below is the code I ran in the Python Console. The output is also below.

layer = iface.activeLayer()
print(layer)
all_features = layer.getFeatures()
layer.startEditing()
for pipe in all_features:

        if pipe['name'] == '1212_1211':
            print('found it ********\n  ')
            pipe_id = pipe.id()

            geom = pipe.geometry()
            print(geom)
            new_feat = QgsFeature()
            geom = pipe.geometry().asPolyline()
            start_point = QgsPoint(geom[0])
            end_point = QgsPoint(geom[-1])
            print (start_point)
            print (start_point.x())

OUTPUT

<qgis._core.QgsVectorLayer object at 0x000001767C312EE8>
found it ********

<QgsGeometry: LineStringZ (26138560.91000000014901161 643574.7099999999627471 778.20000000000004547, 26138558.94000000134110451 643563.81000000005587935 0)>
<QgsPoint: Point (26138560.91000000014901161 643574.7099999999627471)>
26138560.91

UPDATE

I found a great chunk of code from this site that made this work for QGIS 3 – geom.constGet() is the key below. How to access shapefile m-values with pyqgis?

layer = iface.activeLayer()
print(layer)
all_features = layer.getFeatures()
layer.startEditing()
for pipe in all_features:

    if pipe['name'] == '1212_1211':
        print('found it ********\n  ')
        pipe_id = pipe.id()

        geom = pipe.geometry()
        line = geom.constGet() #line returns a QgsLineString object

        z = line.zAt(0) # z value of first vertex
        print(str(z))

Best Answer

It's a bit silly but as I look in the QgsPoint constructor like here: QGIS Python API: QgsPoint

I think you need to provide the 3 coordinates of the point in order to create a 3D point, if you only send a geom and if the wkbtype is unknown, he will cast it as a 2D point. So maybe try to explicitly give the 3 coordinates of the point before calling QgsPoint, something like : 

QgsPoint(mypoint.get().x(),mypoint.get().y(),mypoint.get().z())

and then you do your stuff on mypoint.get().z(). There is also a method called addZvalue().

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