Install SciKit-Image

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

The following nodes become available only when you install SciKit-Image:

• Marching Squares
• Marching Squares on Surface
• Scalar Field Graph

The following node can optionally use SciKit-Image:

• Marching Cubes