A projection augmented model (PA model) is an element sometimes employed in virtual reality systems. It consists of a physical three-dimensional model onto which a computer image is projected to create a realistic looking object. Importantly, the physical model is the same geometric shape as the object that the PA model depicts.
Uniting physical and virtual objects Spatially augmented reality (SAR) renders virtual objects directly within or on the user's physical space. A key benefit of SAR is that the user does not need to wear a head-mounted display. Instead, with the use of spatial displays, wide field of view and possibly high-resolution images of virtual objects can be integrated directly into the environment. For example, the virtual objects can be realized by using digital light projectors to paint 2D/3D imagery onto real surfaces, or by using built-in flat panel displays. Real objects can be physically handled and naturally manipulated to be viewed from any direction, which is essential for ergonomic evaluation and provides a strong sense of palpability. Although simulated haptic feedback devices enable some aspects of computer-generated objects to be touched, they can not match this level of functionality. It is, therefore, unsurprising that physical objects are still used for many applications, such as product design. However, computer-generated objects have a key advantage; they provide a level of flexibility that cannot be matched by physical objects. Therefore, a display is needed that somehow joins the real physical world and computer-generated objects together, thus enabling them to be experienced simultaneously. Tangible user interfaces (TUI) and augmented reality both aim to address this issue. TUI systems use real physical objects to both represent and interact with computer-generated information (Figure 1). However, while TUIs create a physical link between real and computer-generated objects, they do not create the illusion that the computer-generated objects are actually in a user's real environment. That is the aim of augmented reality.
Figure 1 Continuum of advanced computer interfaces, based on Milgram and Kishino (1994). Unlike virtual reality (VR), which immerses a user in a computer-generated environment, augmented reality (AR) joins together physical and virtual spaces by creating the illusion that computer-generated objects are actually real objects in a user's environment (Figure 1). Furthermore, head-mounted-display based AR and VR systems can directly incorporate physical objects. Thus, as a user reaches out to a computer-generated object that they can see, they touch an equivalent physical model that is placed at the same spatial location. Such systems enable the computer-generated visual appearance of the object to be dynamically altered, while the physical model provides haptic feedback for the object's underlying form. However, head-mounted-display based systems require users to wear equipment, which limits the number of people who can simultaneously use the display. A variant of the AR paradigm that does not suffer from these limitations is spatially augmented reality (Figure 1). Spatially augmented reality displays project computer-generated information directly into the user's environment. Although there are several possible display configurations, the most natural type is the projection augmented model.
Projection augmented models
Figure 2 The Projection Augmented model concept A projection augmented model (PA model) consists of a physical three-dimensional model, onto which a computer image is projected to create a realistic looking object (Figure 2). Importantly, the physical model is the same geometric shape as the object that the PA model depicts. For example, the image projected onto the objects shown in Figure 3 provides colour and visual texture, which makes them appear to be made from different materials.
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