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The philosophy is to trace an aperture down the order center, and then cross correlate this trace against an archived solution to identify lines and make a rough fit. Then the lines are re-centroided and and arc solution is written to disk.
Manual Arc Solutions: The X_IDENTIFY GUI
If you wish to inspect the solutions - and you should, at least for the first several tries - you can select "User Reidentify" from the preferences menu. If this mode is called, a GUI will launch to allow the user to check the line centroids and evaluate the fit manually.
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The initial screen of the line ID GUI (based on x_identify from xidl) is shown below:
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