Step 2: Dimension
Because the focal length of camera lenses will vary it is best not cut your rig to specific pre-scripted dimensions but rather test on your cameras to find the desired shot. Have a subject stand at a distance from one of your cameras (make sure the camera is zoomed all the way out). When you have the desired framing in the lens then measure the distance of the camera to the subject. This will be the radius of your camera arc. Keep in mind that you are not limited to an arc and if you have rigging material more flexible then wood you could even reshape the rig to fit the needs of a specific shoot (see the real matrix for demonstration). We went with wood because it was cheap, fast to build, and readily available.
The radius we chose was roughly 5'. To draw the arc we took a 2x4 and drilled a hole in each end. Put sheets of plywood large enough to accommodate your rig down on the floor. In one end of the 2x4 put a pen and anchor the other end temporarily at the center point of the arc. Swing the arm around and draw a nice arc on the plywood (there are probably easier ways to do this involving wire or string). Once you have an arc drawn on the plywood get your cameras and space them evenly around the perimeter. Turn them on and see what it looks like. Put an object in the center of the cameras and adjust them so that they are all centered on the same object. Take a test shot on all the cameras. Make sure you are happy with the range of motion between frames and the proportions and position of the subject to the frame. This is one of the most important elements in getting a good shot in the end and it is one that is hard to adjust once you get the jig saw out, so get it right.
Initially, we made a smaller matrix rig, used velcro to mount the camera and had a session of shots to test the size and spacing. Afterward, we decided to expand the size of the matrix and created a larger platform and increased the spacing between the cameras.