What I’m talking about is not unique to joined fillets. Its everywhere and I have a hard time believing this is something that happens by accident. It has all the earmarks that somebody had the goofy idea that this was some kind of an improvement.
I already reported this previously here after Pascal observed that the individual edge curves of a joined fillet string failed to trim. The cause I suspect is that gaps in the edge curves.The edge curves don’t have their ends at the surface vertices
Here is another example created using Filletsrf and then joining the 2 fillets made.
Bad_Edges.3dm (74.1 KB)
If you check the continuity of the edges using Gcon it will tell you that the edges are not connected.
If you zoom in and look at what is supposed to be a single Brep vertex you will find 2 points that end snap will find:
So, let’s suppose I want to split the basesurf (by isocurve at a point) which one of those snap points will it snap to?
Another problem is that neither of those snap points are the actual BREP vertex location. If you export the polysurface as .stp and re-import you will see what the correct edge definitions are. Those are the edges that Rhino 6 (and every previous version) will make.
The joined edge that Rhino 7 and 8 shows the user is not the valid joined edge that every previous version of Rhino made. How is anybody expected to accurately model when you can no longer rely on object snaps to show the true location of objects?
This is how far off the near snap is in snapping to the true location of an edge:
