<p>A method of determining coordinates for a storage medium (610) includes: determining diffraction data from a plurality of diffraction patterns corresponding to diffractive markers (605-608) of the medium (610); and combining the diffraction data to determine composite coordinates for the medium (610). The composite coordinates may include three translational coordinates and three rotational coordinates. The act of determining diffraction data may include shining a plurality of beams (601-604) on a selection of the diffractive markers (605-608), and measuring the corresponding diffraction patterns in one or more photodetectors (609) to determine the diffraction data. In this latter case the photodetectors (609) may be segmented. The act of combining the diffraction data to determine composite coordinates may include solving a matrix system that couples the diffraction data and the composite coordinates. Each diffractive marker (605-608) may include a pit. The storage medium (610) may include a holographic storage medium.</p>
