Selected posting of mine from previous threads:
I use the Curvature command to check for developability. The command shows the principal curvature circles. A developable surface will have one circle with zero curvature, ie a straight line. Deviation from an exact developable surface can be seen by the deviation from a straight line.
Guassian curvature is a very common metric suggested for assessing if a surface is developable, but it has a significant drawbacks for assessing if a surface is close enough to exactly developable.
An exactly developable surface has exactly zero Guassian curvature. But what is the surface is not “exactly developable” as sometimes happens in design.
How small is small enough for Guassian curvature? That is a non-trivial question, and one that I have rarely seen an answer to.
Is 0.1 small enough? How about 0.001 - that seems like a small number? Or should it be even smaller, perhaps 0.000001?
Gaussain curvature has units of 1/length^2. If millimeters are the length unit then Gaussian curvature has units of 1/mm^2. If meters are used then Gaussian curvature has units of 1/m^2. So the numeric value for the Gaussian curvature of a surface will be 1,000,000 larger if meters are used rather than millimeters. A Guassian curvature of 0.1 if meters are the length units use is the same as 0.009 if feet are used, the same as 0.00065 if inches are used, and the same as and 0.000001 if millimeters are used.
A second drawback to using Guassian curvature to assess if surface is close enough to exactly developable is it is difficult to relate Guassian curvature to other measures such as the amount of twist.