...
A summary of key commands may be obtained using the Help -> Aperture Def Help menu on the menubar.
SET APERTURES FOR BOXCAR EXTRACTION (see below for interactive object profile fitting/optimal extraction)
To define the trace location using the GUI, center the cursor over the emission line (or any location on the image) and press the space bar. A cross will appear to indicate the location of your choice. You may define many crosses and the software will use the median spatial location for the aperture.
...
You may return to the aperture dialog box to readjust your values if you wish. When you are happy, click "done" or type "q" to exit the aperture definition GUI and return to the pipeline. Another xatv GUI may pop up immediately after to confirm your object placement; you can ignore this instance and quit out to proceed with the object extraction.
PROFILE FITTING FOR OPTIMAL EXTRACTION
As an alternative to boxcar/aperture extraction, it is also possible to trim a small region around an emission line to fit a spatial profile to the object for optimal extraction. This feature is in the beta+ stage but appears to work stably. At present, one can only fit to the profile of a single wavelength region from a single order (i.e. around a bright emission line like H alpha). The profile fit in this way is then applied to the entire spectrum. It is not possible to fit profiles on an order-by-order individual basis (it would require some extreme patience anyway).
...