Keywords: sketch-based interfaces, CAE pre-processors.

Two competing approaches exist for creating input data for Computer-Aided Engineering(CAE) applications: stand-alone CAE pre-processors which define both geometric data and attributes, and the combination of CAD applications plus downstream CAE pre-processors. In the CAD-CAE sequence, the former defines the geometric information and the latter adds attributes to the imported CAD geometry. In both cases, data is input through a WIMP (window/icon/menu/pointing device) user interfaces, which are appropriate during the detailed design phase, but clearly inappropriate during conceptual design.

Designers typically draw pen-and-paper sketches to fix their ideas before interacting with WIMP-style CAE pre-processors. This paper describes an entirely new alternative, a sketch-based CAE pre-processor, which allows such conceptual design sketches to be drawn on "virtual paper" and outputs the results in the format required by the desired analysis code. Our prototype implementation is aimed at structural analysis, particularly of two-dimensional bar structures. More generally, we show that sketch-based pre-processors are not merely a valid option in earlier design process stages, but preferable as they increase ease-of-use of user interaction.

Computer interpretation of freehand drawing views mixed with engineering annotations can be traced back to the pioneering work of Hosaka and Kimura [1]. Hong et al. [2] describe the drawbacks of sketch recognisers at this time. Some recent progress has been made. However, the problem of interpreting annotated drawings is still an academic challenge, even before we come to consider the specific problems posed by sketch-based CAE pre-processors.

In our paper, a brief review places the addressed problem in context and introduces the sketch-based paradigm. We then present a sketch-based CAE pre-processor which is innovative in that it simultaneously manages geometric data and attributes in a menu-free environment. Our prototype distinguishes between geometric entities, symbols associated with annotations and gestures associated with editing tasks (i.e. "sketched commands"). Making this distinction permits us to use different recognition strategies for the three types of input.

After processing commands and recognising geometric entities and symbols, our prototype interprets them individually, identifies the relationships between entities, and saves the information into an output file fitting the specifications of the desired analysis code.

The paper includes a brief analysis of current results, and ends with lessons learned and conclusions: the prototype implementation we describe demonstrates the feasibility of sketch-based CAE, and shows that it is a simple and easy-to-use alternative to the alphanumeric inputs of some academic CAE applications currently used for research and teaching.

1

Hosaka M. and Kimura F., "Using Handwriting Action to Construct Models of Engineering Objects", Computer, Vol. 15, Iss. 11, pp. 35-47, 1982. doi:10.1109/MC.1982.1653887

2

Hong J., Landay J., Long A.C., Mankoff J., "Sketch recognizers from the end-user's, the designer's, and the programmer's perspective", Sketch Understanding, Papers from the 2002 AAAI Spring Symposium, pp. 73-77, 2002.

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