I’m no expert, I’ve only been at Rhino for a few months now. Pascal, you really got me thinking about this one. I’m not sure I’m completely convinced anymore either on my exact approach (it certainly doesn’t work across all situations as well as I’d like). But nevertheless there are a number of reasons one might want to layout make the topology follow the edge loop flow (and conversely, a number of reasons to use the standard Rhino tangential spheres).
Curvature Analysis shows that my manual solution is inferior to the tangent sphere in terms of curvature, but it’s still pretty good. I’m not sure the human eye would be able to pick up the differences. The VSR Shape Modeling Multi Blend is 4 clicks/ 4 seconds and blazing fast to execute, but the curvature isn’t quite as good with the default settings (with shading on it looks a bit flat in the centre due to the method for controlling tangency). Depending on how visually/ structurally important the blend is, VSR is most times be my go to solution for this sort of thing. I’ve barely begun to scratch the surface with VSR (and I know one can get better results than what I am getting with it). I’ve been more focused on learning what I can do without plugins.
Here’s some pro’s for what I did and the VSR Multi Blend style of topology for a three-sided blend:
- After converting this type of corner blend to a mesh, the topology is cleaner, more evenly distributed, and symmetrical. Look at the triangles along the edges.
- Texturing will be cleaner (think about where the texture seams are going to be and where the pixels are going to meet). It’s lot easier to layout clean UVs (better aligned UV shells). There is less pixel stretching at UV seams and less texture distortion.
- Am I correct here? The tangent spheres appear to be trimmed surfaces (explode the filleted box and untrim the tangent spheres). There are no trimmed surfaces in my solution.
- What if the result achieved is not the final stage in the modelling process? Starting off with a trimmed surface may not be optimal. Controlling the edge flow/ edge loops in the model can give more control over adding localized detail (and in some cases it may give you the option to use untrimmed surfaces).
- It converts to T-Splines with no issues. It doesn’t work cleanly with a tangent sphere.
- Exporting to other software, having poles and triangles can cause pinching (Zbrush, sub-d surfaces, etc). The topology needs to be as even as possible for subdivision surfaces otherwise pinching will occur and the model won’t sculpt cleanly.
I’ve been trying to work out a somewhat similar method for doing less irregular combinations of surfaces, but it so far I haven’t found a better solution than VSR’s. Some of the methods I’ve been trying have been working pretty well when the surfaces are planar and the input edges have different curvatures. I used a slightly different method for this. The cuts on the three surfaces generated by the one rail sweep need to be made at the centroid of the surface created within the corner points):
It turns out pretty close to the VSR Multi Blend result (but takes significantly longer).
I am just starting to work out a better method for irregular 3-edge non-planar blends. I haven’t quite got it yet but I’m getting there (some issues with tangency), but it’s getting passable (the case in the image, the edges all have different curvatures and concave/ convex).
More or less I’m trying to work out a manual way of doing some of what VSR Shape Modeling does. I own VSR, but I just want to understand more clearly how to create Class A surfaces so my workflow become more intuitive.
Thanks for asking good questions Pascal. It’d be great to get some feedback (or links) from other users. I’ve seen a few good posts and here but I’d still like more information. I hope what I’ve posted is of use/ interest for someone.
cornerBlend.3dm (891.1 KB)