due to reasons of timing I didn’t make it in native Rhino.
I used Icem Surf, but I completly made it manually (no algorithm doing it).
Now I’m pretty sure you can do the same in native Rhino, maybe
with a bunch cps more and much more time.
However owners of the VSR plugin can 100% recreate my workflow, which is:
1.) create unweighted fillets
2.) extrapolate (≈extend them)
3.) create blendcurves
4.) real trim/surface split fillets with blendcurves
5.) create blendsurfaces
6.) trim one blendsurface and match the other blend ontop (isotrim or increase degree to get more cps)
7.) check tangent deviation, match at all surfaces
Unweighted fillets as you see in my example (6 unweighted cps instead of 3 weighted ones in radius direction) are better because matching to weighted (rational) geometry is much more difficult.
You can do so, but it often increases cp count. A low cp count however does not only make it easier to get better smoothness and as a consequence better highlights, it also makes it easier to modify the geometry later on.
In native Rhino, simply rebuilding weighted fillets does work quite often. Its a bit surprising, but when measuring tangent deviation after rebuilding, its often very low. Better of course is using a fillet command which returns unweighted fillets from beginning on (like VSR) .
The problem why its so hard doing corner blends in Rhino, is that Rhino misses this very fundamental modelling functionality. So native Rhino user will get a problem here.
VSR called it “Surface Split”.
Its a trim functionality which also pulls controlpoints back to the boundary.So that the surface stays untrimmed.
Depending on the trimming boundary it could be that there is no solution (more then 4 edges, or unsmooth trimming boundary),however if you use such a functionality the right way, you can pretty fast create the conditions I pointed out (ensuring tangent aligned edges).
Blending at untrimmed edges is much better and allows easy matching.
Here is an example, before:
A good visual deviation analysis would allow to manually match a surface by just pulling cps in normal direction with very low pulling strength. This comes in handy, when the algorithmic approach does not find a good solution or it does but by increasing cp count.
Example of a deviation analysis:
Programms I know being able to get this efficiently are Rhino with VSR, Autodesk Alias, Icem Surf.