Computer Aided Design systems are deemed to be essential for
all the phases characterizing the design and the development of a
new industrial product. However, especially for products characterized
by a strong stylistic content, handmade drawings are often
preferred to CAD software packages.
In the early stage of the development of a new product, esthetic
designers typically produce a rich set of sketches (usually in the form
of orthographic projections) to develop and communicate their
ideas. Product-managers often have to select stylistic alternatives
based on a set of hand-drawings depicting possible solutions.
However,
it is much more effective to base the selection on a virtual
3D model which conveys far more information.
In fact, some hand-drawn alternatives are even ‘‘translated’’ into 3D models (and
possibly rendered models) capable to provide a more realistic view
of the object and to allow a deeper analysis of the design intent.
The translation process, involving a close interaction of esthetic
designers and CAD operators in order to produce a CAD model
carefully representing the designer’s intent, is known to be
considerably time consuming. Accordingly, the design alternatives
available in the form of three-dimensional models result to be a
very small subset of those developed by the designers (usually one
or, at most, two).
The common methodology (Fig. 1) used to turn a set of
orthographic projections into a 3D model starts from arranging the
scanned images of the hand-drawn views on the correspondent
orthogonal planes in a CAD software environment. Using such
images, the CAD operator (often assisted by the designer) manually
redraws the style lines in order to obtain the 3D wireframe model
which is, eventually, used as a support frame for the definition of
the final surfaces.
The automation of this process, i.e. the 3D retrieval from 2D
drawings (known as ‘‘reconstruction problem’’), is a key target for
commercial software houses as well as a vigorous focus from an
academic outlook.
Recently a set of software tools have been released by major
software houses, like Dassault Systemes1, Autodesk1 and PTC1,
which support the CAD operators in some of the reconstruction
process phases. These tools, however, entail a strong user
interaction and only marginally speed up the process. In addition,
most of them require as an input an ‘‘exact’’ set of 2D vector
drawings (e.g. DXF or IGES files).
From the academic point of view, a number of works have been
proposed since the first ‘70s, providing a series of methodologies
for solving the reconstruction problem starting from an ‘‘exact’’ set