FreeDrawer – A Free-Form Sketching System on the Responsive Workbench

Gerold Wesche, Hans-Peter Seidel

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Summary:

The article presents a virtual reality spline based free-form surface sketching system where the user uses a tracked stylus as an input device. The user draws directly in 3D with tools adapted to the needs of designers. The power and utility of 3D environments for design are well recognized. However, most CAD systems are geared toward elaborate shape design and lack support for concept development. FreeDrawer is a sketching tool dedicated to the initial stages of design, enabling direct transfer into a corresponding computer representation.

Unlike direct surface modeling which is based on free-form solids, free form curves or voxel based virtual clay, FreeDrawer constructs models from a skeleton. This approach avoids both computational load and unwanted artifacts when off axis changes are made. Space curves and 2D curves projected on a plane are supported. Standard editing features are accessed from a hand held wand.

A curve network is used to snap new curves to a position in space relative to other curves already drawn, so in effect they are an approximation of the original. When changes are make to a curve, locally connected curves will adapt up to the next junction. Globally connected curves would undergo a collective adaptation.

Filling in surfaces is achieved within closed loops. There is a closed loop algorithm that searches according to geometric criteria. Kuriyama surfaces and n-sided domains can be selected. However, for surface deformation Catmull-Clark surfaces are closely defined to match the Krriyama surfaces. Curve smoothing, sharpening and dragging are achieved with hand gestures where the region of influence is definable.

A novel tool pallet is presented in the form of a set of radially organized pointers rather like fingers, from which the operator can chose. The point of the desired tool is contacted to the point of application and the selection button pressed. An example of a car seat drawn quickly is given to illustrate the performance of the system.

Conclusions:

The utility and at the same time difficulty in implementation of a force feedback system in this type of environment are mentioned. The tool palate is also identified lacking, and in the process of being redesigned based on experience from the current word. An important case is made that unreasonable demands are placed on the ease and usability of 3D drawing environments for the uninitiated.

Discussion:

FreeDrawer seems to target a highly specific window in the design phase which has not yet be liberated from pen and paper. The features and available tools are all tailored to this end and make a highly compelling case.

It is not surprising that the tool palate did not survive in its original form. Trying to touch a particular object would be awkward particularly for some of the tools, not to mention how one would deal with objects close together.

Furthermore, some question is raised as FreeDrawer’s suitability for all designers. Without a test battery this is hard to judge.