Project to a Plane

pyvista.PolyData surfaces and pointsets can easily be projected to a plane defined by a normal and origin

import pyvista as pv
from pyvista import examples

poly = examples.load_random_hills()
poly.plot()

Project that surface to a plane underneath the surface

origin = poly.center
origin[-1] -= poly.length / 3.0
projected = poly.project_points_to_plane(origin=origin)

# Display the results
p = pv.Plotter()
p.add_mesh(poly)
p.add_mesh(projected)
p.show()