In the simplest case, you can install Geomdl by

$ /path/to/blender/2.xx/python/bin/python3.7m -m pip install -U geomdl

but this way you will get pure-python library, which is very slow. If you want it fast, then you have to install Cython (see previous paragraph for instruction). After you installed Cython, you can install "cythonized" geomdl as it is described in Geomdl instruction:

$ /path/to/blender/2.xx/python/bin/python3 -m pip install geomdl --install-option="--use-cython"

To get geomdl to compile

After you install Cython via pip...

Install the same version of Python that your install of Blender uses from python.org

• Blender 2.9 == Python 3.7

This will give you the /includes and /libs. Make sure on the Advanced screen of the installer you choose 'Precompile standard library' and 'Download debugging symbols' After install is complete, open up a Command Prompt (not Powershell). You will be making symbolic links from the /libs and /include from the python installation.

• For the /libs directory

mklink /D "C:\Program Files\Blender Foundation\Blender 2.90\2.90\python\libs" "C:\Users\<username>\AppData\Local\Programs\Python\Python37\libs"

• For the /include directory

mklink /D "C:\Program Files\Blender Foundation\Blender 2.90\2.90\python\include" "C:\Users\<USERNAME>\AppData\Local\Programs\Python\Python37\include"

You should now be able to install geomdl with --use-cython arguments

The following nodes become available only when you install Geomdl:

• Approximate NURBS Curve
• Approximate NURBS Surface
• Interpolate NURBS Surface
• Quads to NURBS
• NURBS to JSON
• JSON to NURBS

The following nodes can optionally use Geomdl:

• Build NURBS Curve
• Build NURBS Surface
• Interpolating Surface
• Interpolate NURBS Curve
• NURBS In