Accurate metrology for focal plane astronomical instruments

Accurate positioning of opto-mechanical elements in the focal plane of large telescopes is a challenging requirements for many state of the art observational scientific applications. In particular high multiplexing multi object spectroscopy requires precise metrology tools for performing efficient observations and calibrations of the instruments. We have developed a metrology system based on modified commercial off-the-shelf components to reach high performances with a cost effective solution. Our system is based on the photogrammetry technique and on a number of fixed off-axis cameras. The cameras acquire images of the focal plane where metrology targets and references are located. The acquisition is based on Odroid-XU4, a single-board computer running on GNU/Linux. No moving parts in the setup ensures an extremely fast acquisition of the data. The calibration and metrology data processing is based on the computer vision library OpenCV. We present a prototype system and results of the camera calibrations and metrology tests obtained in our laboratory.