During the design of an automobile, detailed mockups of the interior are
being built to study the design and evaluate human factors and ergonomic
issues. These physical prototypes are expensive, time consuming, and
difficult to modify.
Immersive virtual reality (VR) provides an effective alternative. A virtual
prototype can replace a physical mockup for the analysis of design aspects
like: layout and packaging efficiency; visibility of instruments, controls
and mirrors; reachability and accessibility; clearances and collisions;
human performance; aesthetics and appeal; and more. A person, placed in a
seating buck, is immersed in the virtual interior and can study the design
and interact with the virtual car.
A seating buck is used for immersive viewing and interactions:
In an 1993-95 project sponsored by Chrysler Corporation, we studied the
process of "Virtual Prototyping", i.e., the many steps required for the
creation of a virtual representation from a CAD/CAM model and for the
subsequent use of the prototype in immersive VR. We implemented a
systematic approach and developed a suit of interactive tools, automatic
algorithms, and data formats that cover the entire process.
The time required for the creation of a virtual prototype was reduced from
several weeks or months to a few hours. This significant step towards the
goal of "Rapid Virtual Prototyping" proved that the application of VR can
shorten the design cycle time, reduce costs, and allow for improved market
response with products that have been optimized through the study of a
larger number of "virtual" design alternatives.
The steps of the virtual prototyping process can be summarized as follows:
Extraction of geometry from CAD/CAM model
Tessellation: approximation of geometry by polygons and
polygon meshes
Complexity reduction: decimation and stitching to various
levels of detail
Prototype editing: color, material properties, vertex
normals, lighting, etc.
Precise texture mapping for the representation of detailed
elements
Additional geometry: external surroundings and other elements
Calibration of virtual display with physical elements of
seating buck
Scripting of functionality and behavior for operational tasks
In the following, some of these steps are briefly explained and
illustrated. For additional background information refer to Virtual
Reality: A Short Introduction.
TESSELLATION AND DECIMATION
The geometry of automotive interiors consists almost exclusively of curved
surfaces. The given CAD/CAM model uses a mathematical representation for
these free-form shapes (e.g., B-splines, NURBS, etc.). The virtual
prototype, however, has to present the geometry via computer graphics
primitives like points, lines, or polygons. Curved surfaces have to be
approximated by polygon meshes using tessellation algorithms. Typically,
large numbers of polygons are created (several millions for an interior).
Decimation algorithms reduce the polygon count to a level that allows for
realtime rendering response at a desired rate of 20 to 30 frames/second
during immersive viewing.
Initial tessellation of a dashboard and result of polygon decimation:
The CAD/CAM model of a surface typically consist of several trimmed surface
patches that are connected along common boundaries. Tessellation and decimation of individual patches create gaps or overlaps between these patches. A
stitching algorithm "sews" the disconnected patches together and creates a
uniform polygon mesh with shared vertices at the patch boundaries.
Stitching along the common boundary of two surface patches:
left: common boundary - center: tessellation - right: stitching Web size (10K) - Screen size (17K)
PRECISE TEXTURE MAPPING
The modeling of elements with complex details like instruments, radio, or
air-outlets requires large numbers of polygons. Texture maps are an
excellent tool to reduce geometric complexity. Computer renderings or
photographs of these elements are converted into bitmaps and a cut-out of
the image is pasted precisely at the correct location within the virtual
prototype.
A photo is converted into a texture map and placed at the correct location:
To place a person properly inside the virtual automotive interior and to
allow for realistic (haptic) interactions with essential elements, a
physical seating buck is used in this application. The buck consists of
seat, steering wheel, foot pedals, and stick shift. The virtual interior is
presented via a stereoscopic display device. A precise calibration of the
virtual display with the physical elements of the seating buck is
instrumental for the usefulness of the virtual prototype. When the user
grabs the virtual steering wheel with the data glove controlled virtual
hand, he or she must feel the physical steering wheel at the very same
location.
The seating buck provides the essential physical elements, an immersive
display device presents the virtual interior at a calibrated location:
For the final use of the virtual prototype, interactions with the interior
need to be defined by specifying the prototype's response to operations by
the user. Functionality and behavior of the prototype is scripted in the
form of event-action relations. For example, if the user touches a radio
button with the data glove (event), sound will be generated (action).
Touching another control may start or stop the windshield wiper. Virtual
pop-up menus can be called up for the modification of interior colors,
lighting environment, and other settings.
Changing the light settings via a virtual pop-up menu:
K.-P. Beier, "Virtual Reality in Automotive Design and Manufacturing,"
Proceedings , Convergence '94, International Congress on Transportation
Electronics, SAE (Society of Automotive Engineers), Dearborn, Michigan,
October 1994.
K.-P. Beier, "Virtual Reality - Advanced Design and Manufacturing," ESD
Technology , Volume 56, No. 1, pp 22-28, January 1995.
