Development of an Augmented Reality system using ARToolKit

Development of an Augmented Reality system using ARToolKit and user invisible markers
To simplify the search for hardware components the problem definition can be split up
into a number of elements. The elements that are encompassed within the problem
definition are invisible marker tracking, stereoscopic video see- through HMD, optical
see-through HMD and ARToolKit. The latter element, ARToolKit is a software
component and was discussed in detail before. The other three elements clearly need to
be supported by hardware components. The second element, a stereoscopic HMD, is to
be expected to be found with the most effort. The difficulty may be presented in the fact
that the HMD will need to have the ability to support both capture and visualization at
the same time. The optical see-through HMD is expected to be found with less effort.
The first element itself can be split up into a small number of sub elements. It was
shown that invisible marker tracking can be accomplished by a configuration composed
of three hardware components [Par04]. It needs to be said that this article was the first
attempt ever to implement invisible marker tracking. To our knowledge, all other
reported cases involving AR based upon ARToolKit make use of visible markers. First
of all, a suitable medium for creating the markers is required. It is fairly trivial that the
medium is to be invisible to the human eye to allow for invisible marker tracking.
Moreover, the medium will need to have certain properties to be able to be detected by
some device other than the human eye. Such a camera is the second hardware
component needed. Finally, to be able to use it together with ARToolKit, the third
hardware component needs to establish the connection between a computer and this
camera.
Now that is known which hardware components are needed, the remainder of this
chapter will, in turn, be devoted to each of those. That approach will give an overview
of the hardware components that possibly could be used. First the three hardware
components for invisible marker tracking will be discussed. The order in which this is
done is the following; invisible marker tracker tracking medium, cameras and finally
connection devices. After that will be treated aspects concerning the HMD system. This
order of representation is chosen because eventually the hardware components for
invisible marker tracking need to be incorporated into the HMD system.
4.1 Invisible marker tracking medium
As described before a suitable medium for invisible marker tracking may not be visible
to the human eye, but should be able to be detected by some other device than the
human eye. Literature study on this topic did not result in much. It appears that in the
AR community all research relies on the usage of fiducial markers, and that invisible
marker tracking has not been paid much attention to up until now.
Somewhat different but related work incorporates imperceptible patterns into images
using a non-intrusive way that enables simultaneous display and acquisition [Cot04].
This is done by modifying off-the-shelf digital projectors in such a way that the patterns
are only visible during a short interval. This non-intrusive approach only minimally
degrades the displayed images. This degration is not noticed because of the ability of
the human eye to recover color constanty. This results in that to the human eye the
embedded patterns are not visible. However, cameras synchronized with the digital
projectors are able to detect them. This basic idea behind this approach provides the
framework for invisible marker tracking.
37