Metrology corrections

After averaging the point data, the only remaining delay correction is the fringe position of the white light source used to monitor the feed system path length. This is implemented as a toggle, i.e. a procedure which applies the correction when called the first time, then removes it when called again, and so forth. The procedure name is whitecorr.

For greater flexibility, the siderostat metrology corrections can also be postponed until after the averaging, in which case they are derived from the averaged XYZ pivot coordinates. This is done by the procedure pivotcorr, the scan data equivalent to the point data procedure metrocorr. It too is implemented as a toggle. It is important however to use pivotcorr before whitecorr, since pivotcorr will have to correct the white light delays too! This is because the white light fringe position not only depends on the feed system path, but also on the pivot motion.

If one decides to apply pivot and constant term corrections after the data has been averaged (so that the changes may be studied more easily), the situation may arise where raw pivot coordinates from the INCHWORM file have to be averaged; this can be done using the inchav procedure.