Environmental Engineering Reference
In-Depth Information
On the other hand, with the method of monovision using mirror, we can set up a virtual
boundary by combining the height of the mirror and the viewing angle of the camera. As
shown in Figure 5B, when the pointer is above the virtual boundary, the image of the
pointer P'
1
will not be picked up by the camera even the pointer P' itself is within the range.
That is, only one image feature will be obtained instead of two. A quick on-off logic can be
easily used to dismiss this single point without calculating the position and distance first.
Since the duration of the pointer in use is often far less than when it is not, demand on
computing power will be greatly reduced.
Fig. 5. Virtual boundary with pseudo-stereovision.
4.2 Action space and virtual force
In previous methods, only the X-direction projection (parallel to the screen) on the camera
image plane is used. It only provides information on the position of the pointer. Move one
step forward, we can take advantage of the Z-direction projection (perpendicular to the
screen) of the image and the time derivatives of the projections for more advanced features.
One such application is to set up an action space immediately outside the touch screen. In
the action space, we can construct virtual forces and use them to achieve the results such as
push, pull, stroke, or other similar motions.
First, let us expand the aforementioned model to a 3-dimensional space with the Z-axis
perpendicular to the display screen and pointing away from it. This 3D action space is
enclosed by the display screen on bottom and the virtual boundary on top. As seen in Figure
6, the pointer can freely move in this space. The projection of the pointer gives a planar
trajectory on the camera image plane.
