3 Replies Latest reply on Mar 14, 2019 6:24 PM by Roland Schwarz

    Symmetry for organic shapes - managing curvature - tips?

    Ryan Navarro

      OK Surfacing Guru's, I have another question for you all!

       

      When planning out your surface models, how do you make sure you won't see visible creases/flat spots/distortions if you are planning to mirror?

       

      I've seen some people struggle with this so much that they refuse to mirror all together. And I'll admit, sometimes it is hard for me to match the smoothness of a continuous spline vs mirrored halves when wanting to model a truly organic form.

       

      Here is what I mean, this is a mistake I used to make (and that I see commonly with beginners) - setting up guide curves and making my splines C2 continuous to the (flat) reference surfaces. This would inevitable result in gross flat spots when mirroring and a visual discontinuity

       

      The "proper" way I've found is to set the profile curves to C1 tangent, and manually adjust them so that there is some curvature at the interface. Having to imagine how much curvature you want at the mirror boundary. I try to make sure that the rate of change of curvature is nearly flat near the mirror boundary to prevent any visible seam.

       

      I'm happy with these results! But... it's a lot of pushing and pulling and tweaking. Is there a way to parameterize this that I'm missing? An easy way to "set" the amount of curvature (specifically for a style spline?)

       

      Attached file in 17 format if anyone wants to play around

        • Re: Symmetry for organic shapes - managing curvature - tips?
          Matt Lombard

          One way is to just not mirror stuff. Or just mirror stuff that doesn't cross the center plane.

           

          Another is to use a curved reference surface instead of a flat reference surface. Don't make a surface c2 to a flat surface because you'll get a flat strip, that should be self-evident.

           

          Another thing to watch out for is mirroring splines within a sketch. These can be really tricky to make sure they're really symmetrical. I would recommend mirroring the spline across the centerline to make sure the mirror lies exactly on top of the original. You can get in a lot of trouble with this, even when it looks good by eye. Splines can get some internal residual tension, such that all the points are symmetrical, but the resulting spline is not.

          • Re: Symmetry for organic shapes - managing curvature - tips?
            Paul Salvador

            Hello Ryan,.. yes, in general, C2 at the center is not always good... and it's a good subject which needs to be brought up over and over again...  I have to constantly check this during and after and of course as a final check before releasing the data to be cut!  (I got burnt one time... major ouch!)

            btw,.. I usually combine both the curvature and zebra to get as much information on deviation/distortion as possible.

            ds3.png

            ds2.png

            • Re: Symmetry for organic shapes - managing curvature - tips?
              Roland Schwarz

              Build half of the surface to the symmetry plane. Maintain the edges normal to the plane. If you do this you will have C2 continuity.