Cultural Heritage.

the simulation whilst some modifications are performed.

3.3 MR registration and staging

Employing a markerless camera tracking solution for registering the CG camera according to

the real one, is an added value advantage since it eliminates the use of external tracking devices

or avoids polluting the real scene with the use of known fiducial markers. However, the issue

that arises is how to geometrically calibrate the camera and define the scene fiducial origin in

world coordinates. Especially as our MR scenes have animated virtual characters, initial character

staging, scaling and orientation is a crucial factor in order to determine correct initial, lifesized,

believable geometrical registration. In the pipeline described in section 4, boujou allows

for an initial scene origin to be defined offline on a tracked scene feature. This feature though is

not sufficient as for a number of characters and a storytelling scenario, designers would like to

interactively direct, stage and adjust the action in real-time, according to their dramaturgical interest.

Therefore we propose a simple algorithm for determining the storytelling scene origin

and orientation, harnessing the features of the underlying OpenGL scenegraph renderer camera

metaphor and world node coordinates as depicted in Fig. 3. We allow for interactive manipulation

of the scene camera as well as separate scene global repositioning and scaling according to

the standard OpenGL formulas for ModelView and Projection matrices: The ModelView and

Projection matrices are used to set up the virtual camera metaphor and are provided in real-time

for each tracked frame, by the underlying camera tracker (Papagiannakis et al 2005). Thus for

interactive authoring-staging in the MR scene, two more controls are supplied: a) A single vector

is mapped via keyboard contols on the translation part of the camera so that the camera can

be furthermore tweaked within the tracked frame and b) A single 4×4 translation matrix is

mapped as a virtual trackball metaphor, so that a designer can interactively stage the “Main

Scene” scenegraph node that contains all the virtual augmentation. Since the basic renderer of

the VHD++ framework is based on OpenScenegraph, all individual elements can have their

transformation matrix modified. However, for the MR real-time authoring stage, it is important

that the whole staged experience can be initially positioned according to the real scene so that

the camera tracking module can subsequently register it accordingly with the real scene.

Fig. 3. Camera Coordinate Systems in MR Fig. 4 Stylized Mediated Reality Extension (The “Visual filter”

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  • h20ho on Jun 6, 2012

    your formatting got messed up.

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