There are also range issues. The larger the physical pattern the further away the pattern can be detected and so the great volume the user can be tracked in. Table 1 shows some typical maximum ranges for square markers of different sizes. These results were gathered by making maker patterns of a range of different sizes (length on a side), placing them perpendicular to the camera and moving the camera back until the virtual objects on the squares disappeared.
|Pattern Size (inches)||Usable Range (inches)|
Tracking is also affected by the marker orientation relative to the camera. As the markers become more tilted and horizontal, less and less of the center patterns are visible and so the recognition becomes more unreliable.
Finally, the tracking results are also affected by lighting conditions. Overhead lights may create reflections and glare spots on a paper marker and so make it more difficult to find the marker square. To reduce the glare patterns can be made from more non-reflective material. For example, by gluing black velvet fabric to a white base. The 'fuzzy' velvet paper available at craft shops also works very well.