The difference between length and LastParameter?

[microelly2]

What is the difference between length and LastParameter for a curve?

>>> bc.length()
221.19932268800784
>>> bc.LastParameter
203.44541715547686

And what is the meaning of curvatureAt for a Face?
Are the values the main curvatures or the curvaturesfor the two iso-curves trough the point?


f=App.ActiveDocument.Torus.Shape.Face1
f.curvatureAt(0,6)
(0.08054889713478175, 0.5000000000000001)

[DeepSOIC]

What is the difference between length and LastParameter for a curve?

LastParameter is the parameter value of the ending vertex. Length is length. LastParameter in general has no relationship to Length since parametrization is an arbitrary thing.

Parameter is t in parametric equation of the curve "r = (x(t), y(t), z(t))". The actual curve is a set of x,y,z points, parametrization is just a very convenient way to define curves. Length is a property of the curve, and doesn't depend on chosen parametrization. LastParameter does depend on parametrization.

I would guess, these values are so close in your case because "chord length" knot vector construction was used. In this case, LastParameter is probably equal to the length of polyline connecting points being interpolated.

[Chris_G]

Code: Select all

And what is the meaning of curvatureAt for a Face?
Are the values the main curvatures or the curvatures for the two iso-curves trough the point?


f=App.ActiveDocument.Torus.Shape.Face1
f.curvatureAt(0,6)
(0.08054889713478175, 0.5000000000000001)

These are the principal curvatures : the min and max curvatures
https://github.com/FreeCAD/FreeCAD/blob ... p.cpp#L480
If you're looking for the curvature in a specific direction, I found this topic that could help :
https://www.opencascade.com/content/spe ... -curvature

EDIT : oops, sorry, it looks like the DUV derivative used in the algorithm above is not ported to FreeCAD.

[microelly2]

These are the principal curvatures : the min and max curvatures

Well, that was what I'm looking for. So I can find the developable areas
Thank you.