SOLIDWORKS Industrial Designer (SWID) comes with a library of freeform subD primitives that can be shaped like digital putty. Two of the most popular primitives are the “globe” and the “quadball”. Both these primitives are spherical in shape. Why then does SWID have two similar shaped primitives and when does a designer use one over the other?
Globe: The globe is the closest thing in SWID to a true sphere. If your design has anything that is spherical, such as a dome, use the globe primitive.
The downside of using the globe is that you need to be careful about deforming the shape at the poles. The poles of the globe primitive comprise triangular faces where many edges come together at a single vertex. An apt analogy is the lines of longitudes on a model of the earth meeting at the poles and the Arctic Circle cutting them to make triangular faces.
A vertex where more than four edges meet is called a “high valence vertex”. When such high valence vertices are pulled to deform the shape, the surface around it starts to ripple.
These triangular faces can be deleted using the Delete command and they can be filled back using Fill command. In this case, SWID use quads instead of triangles to fill the gap (see figure above). The catch is that now the shape is no longer spherical. So if you wanted a true “dome” shape you’d lose it if you used this technique.
Quadball: A Quadball is a rounded out cube; it only appears to be spherical. The quadball is one of the most versatile primitives in SWID. It works great for most design scenarios. The only downside to using the quadball is the fact it appears spherical when it really is not, and is therefore visually misleading to some users. All the faces on the quadball are four sided, so it is a true quad mesh all around. Consequently this puts out the highest surface quality. That being said, you can still get into high valence situations if you start sub-dividing.
My thanks to Rob Jost, SOLIDWORKS Product Definition Senior Manager, for his insights on this topic. Also, check out these fantastic models that Rob created using quadballs.