Freeform modeling is an integral part of the geometric modeling and design process. Existing freeform modeling systems expect the user to be familiar with the geometric representation and user interface in order to model precisely and rapidly. As a result, modeling complex freeform geometries precisely and rapidly can be quite difficult. In this thesis, we address the problems manifested in current freeform modeling systems. We introduce a novel modeling approach called "Guided Trace and Stitch" (GuTS) which designs curves and surfaces precisely, fluently and rapidly. To achieve its ends, the GuTS modeling approach has multiple components - tracing, snapping, stitching, and a multimodal user interface. GuTS creates new curves and surfaces by tracing predefined geometries to create an accurate replica of the existing model, hence achieving precision. The GuTS modeling approach also allows multiple geometries to be snapped together. As a result, multiple geometries are easily and rapidly traced over and stitched together to create a complex geometry, hence achieving rapidity and precision. The GuTS modeling approach raises several challenges for user interaction in interactive modeling. However, to address these challenges, we implemented the idea of a multimodal user interaction which uses two-handed input, 3-dimensional mouse input, pen and data tablet, voice input, and synthesized speech output. Basically, the goal was to create a user interaction which adapts natural interactions in the modeling realm. This multimodal interface is designed in such a way as to provide fluent and direct interaction. Further, the simultaneous use of multiple input and output modes through effective coordination provides rapid interaction. We also implemented a software system based on this approach called the "GuTS System." The GuTS modeling approach is independent of the underlying data structure. To demonstrate, the GuTS approach is implemented using Subdivision curves and Bezier curves representation in two-dimension, and using tessellated geometry representation in three-dimension. This system demonstrates that the GuTS modeling approach is feasible. Using the GuTS system, we created several sample complex freeform geometries to demonstrate the practical usability of this system.

@PhdThesis{Ara07,
  author       = "Arangarasan, Rajarathinam",
  title        = "Guided Trace and Stitch Modeling Using Multimodal Interaction",
  school       = "University of Wisconsin - Madison",
  month        = "may",
  year         = "2007",
  url          = "http://graphics.cs.wisc.edu/Papers/2007/Ara07"
}