3.3.1 Determining the Flare Location on the Sun (HXT Address)

Before starting HXT image synthesis, we need to know the flare location on the Sun, in the HXT coordinates (whose origin is the HXT optical axis and unit is the HXT pitch (= 126). East and north are positive). The most convenient way to do this is to run the following program:
IDL> xy0 = get_hxt_pos('15-Nov-91 22:37')
  Here '15-Nov-91 22:37' is the (approximate) date and time of the flare for which you want to make images. Values contained in xy0 (= fltarr(2)) are used in the next image synthesis procedure.

The routine GET_HXT_POS will perform the following checks in this order until it finds a match.

1. Read the $DIR_HXT_CAL/hxt_flare_pos.txt file to see if the time is in that list.
2. Use the GOES heliocentric location to determine the address
3. Use an SXT image index to define the address
4. Pass in heliocentric coordinates and convert them
5. Ask the user to specify the HXT address directly

See the Reference Guide for more details on GET_HXT_POS.