Intersecting surfaces yields G0 trim edges

[Anonymous]

Ages back I learned that projected curves lose a level of continuity, so for example if you trim a surface using G2 curves, the trim edges will only be G1.

However, after all these years, I'm stunned to discover that not even intersected G3 connected surfaces are guaranteed to yield G2 or even G1 continuity after trimming:

 Why is this and are there any similar rules of thumb that govern this?

(NOTE: The attached .step file example is only G2.)

[BarryKimball]

you are using the "Curve Curvature" tool to analyze a surface edge...to do this you must set the Curve Curvature setting to"surface normal" in the information window.

[Anonymous]

Thank you for the reply!

@BarryKimball are you able to comment on the rule of thumb I was taught? "Projected curves will lose one degree of continuity, so for example if you trim project with G2 curves the resulting trim edges will be G1"...

[c3systems]

@Anonymous 

Haven't heard that thumb rule till now. Don't really understand the need for mathematical continuity for the trim edges. Are you trying to build of surfaces from the trim edges? Hope this is just a curious discussion.

Anyway regarding the thumbrule; Don't agree to it completely, but there could be some truth in it. Internally, Alias CoS is defined as a degree three curve, sometimes even with "hard" knots in between. Although, degree 3 curves (multispan) can have higher order geometric internal continuity, the parametric internal continuity is limited.

[50230632]

i have check you data

at first ,surface  continuity is not good,just g2

if we want to interset line have good continuity,

so surfaces neet to better,just like the a class defined

afert modify surfaces,the intersect edge have nice and continuity