[vtkusers] Re: Compute principle curvaturs

[Goodwin Lawlor]

Hi Moti,

What formula did you use for the principal curvatures (k1 and k2)?

With
K (Gaussian) = k1.k2
H (Mean) = (k1 + k2)/2

the quadratic solves as

k1,2 = H +/- sqrt(H^2 -K)

testing if  H^2 - K > 0, leads to (k1 - k2)^2 > 0 which is true... so you
should get a solution for k above, if H and K are correct. Perhaps some
unusual geometry is causing problems calculating H and K initially. You
should test H^2 - K > 0 for each point before you get the principal
curvatures. If the test fails mark the point as undefined and move on to the
next point.

I would be easy enough to add this into vtkCurvatures
(SetCurvatureTypeToMaximumPrincipal etc.)

hth,

Goodwin


"Moti Freiman" <freiman at cs.huji.ac.il> wrote in message
news:000101c45d02$22c4d820$2a284184 at cas02...
> Hello!
> I need to compute the principle curvatures at my software.
> I saw that the vtkcurvatures class just compute the mean and Gaussian
> curvatures. When I used the formula for extracting the principle
> curvatures from mean and Gaussian,  I got undefind situation (negative
> sqrt). Do someone know how I can get the principle curvatures with vtk?
> Thank you
> Moti freiman
>
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