US Patent 7287701 Handheld coordinate reference system

A method and apparatus for determining a spatial position of interest in an assembly is disclosed. In one embodiment, the method comprises the steps of determining a reference position of reference unit; moving the reference unit from the reference position to the first spatial position; inertially measuring a displacement of the reference unit while the reference unit is unilluminated by an illuminator; and determining the first position from the reference position, illuminator energy reflected from the reference unit, and the inertially measured displacement of the reference unit.