Question about the shape of this object

unhandled

#1

In the images, I see that my U and V curvature graphs in the aft ship should create a spheric shape as these are both convex.
However, the Gaussian analysis indicates a large hyperbolic, blue area which would be a combination of convex and concave.
Can anyone tell me what’s happening here?

The Gaussian Analysis mesh is quite refined.




(Pascal Golay) #2

Hi Gerard - the range shown in the Gaussian curvature analysis is essentially zero, am I reading that right?

-Pascal


#3

Yes Pascal,

That’s totally right and for creating developable surfaces, I use ranges of:

1e-08 tot -1e-08
1e-09 tot -1e-09
1e-10 tot -1e-10

This depends on the vessel size.


(David Cockey) #4

My guess is the U and V curves are not aligned with the principal directions of curvature. Guassian curvature is based on principal directions of curvature. Use the Curvature command to explore the principal directions of curvature.

Guassian curvature is both object size and unit size dependent. It varies inversely proportional to the square of the size of the object, and inversely proportional to the square of the size of the length units used.


(David Cockey) #5

Example of a simple surface with U and V curvatures with the same sign, but an area of negative Guassian curvature: Negative Guass Curve DC01.3dm (59.3 KB)


#6

This is very valuable information David,

It confirms my idea (conclusion) that the curvature graph is leading regarding analyzing convex/concave shape. I already found out that the Gaussian analysis depends highly on the size of the object. As I always model in mm, I was not aware of the dependancy on units.


#7

Your example shows explicitly your explanation. Thank you David.