The use of moiré patterns to detect alignment problems

Using a moiré pattern it is possible to detect very slight misalignments. For each rotational parameter (yaw, pitch, and tilt) the figure shows the resulting configuration in space (left column), a misaligned rectangle projected against a reference rectangle (middle column), and the moiré pattern visible on the screen using our technique (right column). To adjust yaw, we use horizontal stripes to form a moiré pattern (top right). The moiré stripes diverge to the right for a projector pointing to the right. To adjust pitch, we use vertical stripes to form a moiré pattern (middle right). The moiré stripes diverge toward the top for a projector tilted upward. Either direction can be used to adjust tilt (bottom right). The orientation of the moiré stripes show the direction the tilt.