Rather than defining a lot of different NURBS primitives (sphere, cylinder, plane, disc, etc), solidThinking delineates just two primitives: a NURBS surface and a NURBS curve. By appropriately setting the control points and knot vectors the NURBS curves and surfaces can be used to model any shape.
The advantage is that even if they represent different shapes, the primitives are always the same. This means that the same operation applied to a sphere (a trimming, for example) can be applied to a cylinder or to any other shape, since the underlying primitive is always a NURBS surface.
Primitives of revolution (sphere, torus, cylinder, and disc) can be created with or without weight. Using a sphere, for example, we can create an exact sphere if we use weight, while we will only obtain an approximation of an exact sphere if we don't use it.
Note: In general, you can use weight if you do not plan to modify the original shape. A non-weighted surface provides greater flexibility for editing.
As usual, the modeling tool panel offers a number of options to modify parameters and/or apply new commands. Each parameter/command can be modified/applied by working in the views only, in the Modeling Tool panel, or in both Views and Modeling Tool panel.
For each parameter/command we will mention all the possibilities as follows:
Views: steps to follow allow you to work in the views only;
Modeling Tool panel: steps to follow allow you to work in the Modeling Tool panel only;
Views / Modeling Tool panel: steps to follow require you to work in both views and Modeling Tool panel.