Flatness Measurement of Large Flat with Two-Station Laser Trackers

We present a novel method to accurately measure the flatness of a large flat. The method can be seen as a task-specific error correction of the laser tracker. Laser trackers are positioned at two specific measuring stations and measure the coordinates of the same sample points. The angular errors of the primary laser tracker are compensated with constraint information provided by an additional laser tracker. Using this method, we measure the flatness of a 4.5m flat. The flatness measurement uncertainty is 1.4 mu m in rms (root mean square).