Game Development Reference
In-Depth Information
tp://reactivision.sourceforge.net/
)
. It was developed for the fast tracking of fi-
ducials. The markers have a very unusual, bionic appearance, like that of an
amoeba. This geometric shape is not accidental; some topological informa-
tion is stored inside such markers. Unlike the traditional 2D bar codes, the
reacTivisionmarkersstoresdatatreeinformation. Thedesignissosmartand
logical that it helps to remove some stages from the digital-vision algorithms.
There are some specially coded vertices and edges inmarkers. That is why
the design is so organic and don't use any square shapes. The concept is
simply genius! The full story is covered in the article
The Design and Evolu-
tion of Fiducials for the reacTIVision System
by Ross Bencina and Martin
Kaltenbrunner (
http://mtg.upf.edu/node/442
).
The overall list of available marker designs is much longer; for instance, there are
fiducials such as the
Hoffman marker system
(
HOM
),
Institut für Graphische
Datenverarbeitung
(
IGD)
markers, and some others. In most cases, their structure
is very similar: a thick and contrasting outline and a pattern made of square blocks.
The problem with printing fiducial symbols can be resolved in various creative ways.
First of all, the product itself should be so exciting and intriguing that the audience
will try their best to find a way to print the marker. Moreover, some types of fiducial
markers have a graphic structure that is based on simple geometric forms, for ex-
ample, SCR or reacTIVision markers may be drawn by hand. Only a piece of paper
and a black magic marker are needed. The piece of paper should be taken by a
player and applied on screen where a PDF document that contains fiducial markers
is shown. Because the paper is translucent, all the shapes can be easily traced. Of
course, there can be some inaccuracies, but in many cases, they are irrelevant and
the AR works successfully.
Note that if your game uses fiducials, a graphic document with a marker must be
uploaded on the homepage of your website. It is also good to have a special test
page with the marker displayed clearly so players have the chance to test AR in
the game without printing anything, for example, you could use a computer monitor
or another mobile device (an iPad can be made to act as a marker). Such practice
prevails in the cute game
Om Nom: CANDY Flick
from ZeptoLab UK Limited (
ht-
The following figure demonstrates concepts of fiducials that don't need a printer and
can be done by hand:
