Surface Matching problem

Hi all.
I’m having problems matching these 2 surfaces to a curvature continuity.
But also noticing that even positional continuity match makes it so that the Control Points don’t line up.
What can be the problem and how can I solve it?

Thanks in advance

why.3dm (35.9 KB)

Hello - the surfaces are rational - the middle control points are not weighted at 1 and not the same on each surface. If you set all weights to 1 (Weight command) , then the match will line the points up as you expect.


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The surfaces have a different structure.
If they were built the same would this matching not be in question?

The surface on the left (more curved) is:
NURBS Surface (rational)
“U”: degree =4 CV count = 5 (-131.256 <= U <= -0)
“V”: degree =2 CV count = 3 (-179.722 <= V <= -0)

The surface on the right is:
NURBS Surface (rational)
“U”: degree =3 CV count = 4 (-267.666 <= U <= 0)
“V”: degree =2 CV count = 3 (-0 <= V <= 262.452)

I believe it is just the rational-ness across the V, with different weighting as well, that is causing trouble; the U direction structure is clean on both.
That said, changing the V degree to 3, once the point weight has been set to 1 all around, does allow a cleaner match - not sure why that should be if the points all match up.


Hi Pascal.
I was thinking about the Weight issue, it crossed my mind.
However what would cause it to automatically change the weights if I didn’t do it manually (i didn’t)?
Setting weights on just the middle points doesn’t do the trick, seems other points are also at play. That said, is there (should there be) a command that with a selected surface sets all the CVs at 1?

Thanks for the help. Fixed the issue.
Still would be nice to know how to prevent weights changing without explicitly setting them.

Most likely the surfaces or the curves that generated them, used arcs/cylinders/spheres or some other rational geometry at some point in their existence.