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I'm developing a standalone QGIS application and I want to run the tessellate (3d:tessellate) processing tool using the following code: 

import processing
from qgis.analysis import QgsNativeAlgorithms
from qgis.core import QgsApplication
from processing.core.Processing import Processing

# Supply path to qgis install location
QgsApplication.setPrefixPath("C:\\OSGEO4~1\\apps\\qgis", True)

profile_folder = '.'
# Create a reference to the QgsApplication.  Setting the second argument to False disables the GUI.
app = QgsApplication([], False, profile_folder)

# Load providers
app.initQgis()

Processing.initialize()
QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
processing.run("gdal:aspect", {'INPUT': 'D:/OneDrive/Personnel/Daniel/QGIS/Kingston/Kingston_sub9.gpkg|layername=Road', 'OUTPUT': 'TEMPORARY_OUTPUT'})

# Stop QGIS appllication
app.exitQgis()
app.exit()

I received the following error message saying it cannot find the algorithm:

C:\OSGeo4W64\apps\Python37\python.exe C:/Users/berge/PycharmProjects/qgis_geo_sim/runner_chordal_axis.py
C:\OSGeo4W64\apps\qgis\python\qgis\utils.py:744: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
  mod = _builtin_import(name, globals, locals, fromlist, level)
Traceback (most recent call last):
  File "C:/Users/berge/PycharmProjects/qgis_geo_sim/runner_chordal_axis.py", line 19, in <module>
    processing.run("3d:tessellate", {'INPUT': 'D:/OneDrive/Personnel/Daniel/QGIS/Kingston/Kingston_sub9.gpkg|layername=Road', 'OUTPUT': 'TEMPORARY_OUTPUT'})
  File "C:\OSGeo4W64\apps\qgis\python\plugins\processing\tools\general.py", line 106, in run
    return Processing.runAlgorithm(algOrName, parameters, onFinish, feedback, context)
  File "C:\OSGeo4W64\apps\qgis\python\plugins\processing\core\Processing.py", line 125, in runAlgorithm
    raise QgsProcessingException(msg)
_core.QgsProcessingException: Error: Algorithm 3d:tessellate not found

But I can run the same processing tool code in the QGIS python console and it's working fine:

processing.run("3d:tessellate", {'INPUT':'D:/OneDrive/Personnel/Daniel/QGIS/Kingston/Kingston_sub9.gpkg|layername=Road','OUTPUT':'TEMPORARY_OUTPUT'})

When I run the following code in the QGIS python console I can "see" what are the runnable processing tools and of course 3d:tessellate is there

for algo in QgsApplication.processingRegistry().algorithms():
    print(algo.id(), "------", algo.displayName())


3d:tessellate ------ Tessellate
gdal:aspect ------ Aspect
...passing 950 lines...
saga:zonalmultipleregressionanalysispointsandpredictorgrids ------ Zonal multiple regression analysis (points and predictor grids)
saga:zonalrasterstatistics ------ Zonal raster statistics

When I run the almost same code in a QGIS stansdalone script I have the following output and do not see the 3d:tessellate processing tool.

gdal:aspect ------ Aspect
gdal:assignprojection ------ Assign projection
... passing 949 lines...
saga:zonalmultipleregressionanalysispointsandpredictorgrids ------ Zonal multiple regression analysis (points and predictor grids)
saga:zonalrasterstatistics ------ Zonal raster statistics

What is wrong? Why I cannot "see" and use the tessellate "3d:tessellate" processing tool in a QGIS standalone application?

I used the following for this test:

  • OS: Windows 10
  • Version: QGIS 3.12
  • Installation: OSGeo4W64
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Because 3d is not part of the "native" plugins you load when executing PyQGIS in standalone (or the namespace of the functions will be native:tessellate instead of 3d:tessellate When you look at the code, you see that you would need a Qgs3DAlgorithms https://github.com/qgis/QGIS/blob/3b3c7d8012407e14fb24b684bb8a623836202f4a/src/process/qgsprocess.cpp#L174 Infortunately, you need sip bindings to expose the C function to Python and it's not the case at the moment. You may do a feature request or make a PR to support 3D algorithm within PyQGIS on the official tracker https://github.com/qgis/QGIS/issues

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