GT_HXA will extract the HXA data from a ATR structure or
from an ADA data structure. Some sample calls are:
IDL> hxa = gt_hxa(atr)
IDL> sxtcen = gt_hxa(atr_data, /sxtpix)
IDL> sxtcen = gt_hxa(atr_data, /sxtpix, /x)
IDL> hxacen = gt_hxa(atr_data, /hxacen)
IDL> hxacen = gt_hxa(atr_data, /hxacen, /y)
IDL> x1 = gt_hxa(atr_data, 0)
IDL> x2 = gt_hxa(atr_data, 1)
IDL> y1 = gt_hxa(ada_data, 2)
The hxa result would be 4xN where there are four addresses
for HXA limbs.
The /x or /y switches will result in a
single address being returned, and the /sxtpix will return
the results in SXT pixel coordinates.