Orders can usually be located completely automatically by ECHOMOP. The algorithm takes the central few columns of a the frame and cross-correlates them to provide an estimate of the average order separation.
It then uses this estimate to size a sampling box. The central columns are then re-sampled using averaging and a triangle filter to enhance the central peaks. The resulting data is then searched to find the peaks representing the centre of each order.
This technique can be severely affected by cosmic rays and other high-energy contaminants in the image. It is recommended that only flat-field (or bright object) frames are used to perform order location and tracing.
In cases where the algorithm cannot locate all the orders which are apparent by visual inspection, the orders may be located manually. To control this TUNE_AUTLOC=NO should be set. In this case ECHOMOP will display a graph of the central portion of the frame and wait for interactive verification of, or correction to, the located order positions. For cases where the user is confident that the located orders will be correct, TUNE_AUTLOC=YES can be specified.
A typical interactive plot appears below.
Martin Clayton