These routines will extract the average counts/sec of all 64 sensors.
The input can be roadmap, index, or observing log and it will
get the proper structure tag and decompress it properly to
return counts/sec/sensor.
It is possible to get a string defining the
channel selected by using the title keyword option.
IDL> y = gt_sum_l(roadmap)
IDL> y = gt_sum_l(w_h, title=title)