


Everything is square and symmetrical, fill in the appropriate dimensions accordingly. The dots are LEDs, 16 per face. The primary dimension of the box could actually be anything between 12 in. to 17 in. Actually, the 12 in. design uses less material so is probably best with respect to cost and ease of handling.

This iso view only shows how the LEDs are spaced around the 5 visible faces of the cube (there are no LEDs on the base). From any camera imaging the cube, at least two faces will be visible.
Because the LEDs are under programmatic control, we can turn one LED on at a time. This makes determining point correspondences very easy. The actual calibration benefits from as many points as may be feasibly extracted. Because each camera will only be able to see at most 48 LEDs (3 faces 16 LEDs per face) it would be nice to add additional features that may easily be extracted from the images to increase the total number of point correspondences. These features will be passive such as a checkerboard pattern or dots on the surface of the cube. Having the additional passive features allows us to compare calibration techniques that use only passive components with those that also use active elements (like the LEDS).
This view shows one face of the cube with both the LEDs and a passive checkerboard pattern. The edges between the white and black squares can easily be detected and used to extract features with subpixel accuracy (this is because the lines may be integrated over their length).
Color is an important visual cue and is often used in computer vision systems. Unfortunately color varies greatly across cameras and is highly dependent upon lighting. Even within a single room, different locations will be lit very differently. One of the most striking examples of this variability comes from rooms that have a window allowing sunlight to stream through as well as parts that are lit only by flourescent lights.
In order to use color across cameras it is important to ensure that the cameras are color calibrated to the same target object. Adding color to the calibration cube would make it easy to ensure that all the cameras image the same target color source under approximately the same lighting conditions. Thus I would like to somehow add swatches of color to the cube, perhaps using the colors from the ColorChecker (shown below). It would be nice to use the color to also implement the passive image features, but the differing contrasts between various color swatch pairs may introduce biases??? Regardless of how color is used, it is important that the color surfaces be as lambertian (non shiny) as possible to minimize the impact of the camera's viewing angle.

The GretagMacbeth ColorChecker (previously known as the Munsell ColorChecker). The colored squares are essentially matte paint chips that try to be as Lambertian as possible (i.e., they try to reflect light equally in all directions).
This is one example of using color on the cube. Somehow we need to
be able to paint the various squares with a matte finish. Shiny
surfaces won't do because reflections will kill us. The surfaces need
to be very scratch resistant and the edges need to be sharp and
accurately located.
Probably the best solution from a technical standpoint, this
configuration could present manufacturing difficulties. The black and
white checkerboard pattern could easily be recovered (the colored
circles masked out) by the calibration routine.