Freeform surfaces are surfaces that are non-analytic, i.e. they cannot be defined as a plane, cylinder, toroid or cone. These surfaces are defined using Basis-Splines (B-Splines) or Non-Uniform Rational Basis-Splines (NURBS). There are many surface modeling tools on the market that specialize in the creation and manipulation of freeform surfaces. Many of these do not generate volume solids, but rather interact directly with the surface geometry. This technology has been around for many years. There are also many solid modeling systems that have freeform surface design capabilities. This technology is a bit more complex in that connectivity must be maintained to form a solid, even during editing.
History-based modeling has simplified the problem of freeform surface design in a solid model by making the development and modification of these complex surfaces “history-based”. In other words, with history-based modeling you capture the process of creating the surface in the history tree. Rather than directly manipulating the 3D surface, history-based modeling allows you to go back to the original sketches and parameters that were previously captured in the history tree, modify them as necessary, and then regenerate the model. With this technology there is no need to directly manipulate the surface and try to maintain connectivity. It greatly simplifies the problem – that is, IF you create the part correctly in the first place.
With history-free direct modeling there is no history tree. As such surface design and manipulation can be more complex. The system can certainly provide a variety of surface creation capabilities, but when it comes time to modify the surfaces there are no 2D sketches to go back to. The interaction must be done directly on the surface while maintaining connectivity and continuity – in a predictable way. It is certainly not a trivial task and there are still many challenges, although progress continues.
The video below is the first of several videos that I hope to do regarding history-free solids-based freeform surface design (or something like that). This first video is a simple example that only shows a small subset of the freeform creation and editing capabilities. As usual I will be using CoCreate Modeling for these videos, but if the other makers of history-free direct modeling systems (Spaceclaim, Kubotek) want to add to this, I will be glad to include links in other posts.