Strain map from deformed point surface

i have a surface described by points only
The surface data is in two conditions - relaxed and stretched
i would like to get the strain / stretch map pf the stretched condition. what is the way to do it?

I know that GOM Correlate can do it for 3D scans using digital image correlation. In ParaView, you would have to calculate it “manually” using the definition of strain:


where u is displacement.