Creating 3D points in PyQGIS?

Question

The python version of QgsPoint takes just two floating point parameters, unlike the C++ equivalent. The QGIS API docs for QgsPoint gives this example:

pt_z = QgsPoint(120, 343, 77)
pt.exportToWkt() # PointZ(120 343 77)

Here is an excerpt from the error message in a python script

point = QgsPoint( wp.longitude, wp.latitude, 0.0 )
TypeError: arguments did not match any overloaded call:
QgsPoint(): too many arguments
QgsPoint(QgsPoint): argument 1 has unexpected type 'float'
QgsPoint(float, float): too many arguments

The call works fine without the third parameter.

How do I add 3D points from a python script?

Answer 1

For QGIS v3.x

You can use QgsPoint directly:

zPoint = QgsPoint(-74, 4, 2600) # x, y, z
zPoint.z()  # Prints 2600.0

Should you need a QgsGeometry object, just use:

my_geom = QgsGeometry(QgsPoint(-74, 4, 2600))

For QGIS < v3.0 and >= v2.10

You need to use QgsPointV2:

zPoint = QgsPointV2( QgsWKBTypes.PointZ, -74, 4, 2600 ) # type, x, y, z
zPoint.z()  # Prints 2600.0

---

This is an example with a memory layer using QGIS 2.14 (based on the PyQGIS Cookbook):

from PyQt4.QtCore import QVariant

# create layer
vl = QgsVectorLayer( "Point", "Points with Z", "memory" )
pr = vl.dataProvider()

# add fields
pr.addAttributes( [QgsField("name", QVariant.String),
                    QgsField("age",  QVariant.Int),
                    QgsField("size", QVariant.Double)] )
vl.updateFields() 
QgsMapLayerRegistry.instance().addMapLayer( vl )

# add a feature
fet = QgsFeature()
fet.setGeometry( QgsGeometry( QgsPointV2( QgsWKBTypes.PointZ, -74, 4, 2600 ) ) )
fet.setAttributes( ["Johny", 2, 0.3] )
pr.addFeatures( [fet] )
vl.updateExtents()

# Read feature's geometry
f = iface.activeLayer().getFeatures().next()
g = f.geometry()
g.geometry().z()  # Prints 2600.0
g.geometry().asWkt() # Prints u'PointZ (-74 4 2600)'
g.exportToWkt()  # Prints u'PointZ (-74 4 2600)'

Answer 2

In QGIS 3, this was working for me. I had a long troubleshooting session to figure out that the brackets needed to go inside the addFeatures(). I truncated the code a bit so it would fit here.

struct_layer.startEditing()
this_struct = QgsFeature()
fields = struct_layer.fields()
this_struct.setFields(fields)
x_pos = 26131826.00
y_pos = 643499.00
z_pos = 777.00
this_struct.setGeometry(QgsGeometry(QgsPoint(x_pos, y_pos, z_pos)))

struct_data.addFeatures([this_struct])    
struct_layer.updateExtents()              
struct_layer.commitChanges()
struct_layer.triggerRepaint()