HDU classes

Following NASA’s recommendation (see HFWG Recommendation R8), a hierarchical classification is applied to each HDU within DL3 FITS files, using the HDUCLASS and HDUCLASn keywords.

Some useful links from other projects:

• http://cxc.harvard.edu/contrib/arots/fits/content.txt
• https://heasarc.gsfc.nasa.gov/docs/heasarc/ofwg/docs/ofwg_recomm/r8.html
• https://heasarc.gsfc.nasa.gov/docs/heasarc/ofwg/docs/ofwg_recomm/hduclas.html
• http://www.starlink.rl.ac.uk/docs/sun167.htx/sun167se3.html
• https://confluence.slac.stanford.edu/display/ST/LAT+Photons

The different HDUs defined in the current specifications are listed here:

• EVENTS : Table containing the event lists. See EVENTS.
• GTI : Table containing the Good Time Intervals (‘GTIs’) for the event list. See GTI.
• POINTING : Table containing the pointing direction of the telescopes for a number of time stamps. See POINTING.
• RESPONSE : Table containing any of the different instrument response function components defined in the specs. See IACT IRFs.

The current HDU class scheme used is the following:

• HDUCLASS : General identifier of the data format. Recommended value: “GADF” (for “gamma-astro-data-formats”)
• HDUDOC : Link to the DL3 specifications documentation
• HDUVERS : Version of the DL3 specification format
• HDUCLAS1 : General type of HDU, currently: EVENTS, GTI or RESPONSE
• HDUCLAS2 : In case of RESPONSE type, refers to the IRF components stored within the HDU: EFF_AREA, BKG, EDISP or RPSF
• HDUCLAS3 : In case of RESPONSE type, refers to the way the IRF component was produced (POINT-LIKE or FULL-ENCLOSURE)
• HDUCLAS4 : In case of RESPONSE type, refers to the name of the specific format

HDUCLAS1	HDUCLAS2	HDUCLAS3	HDUCLAS4
EVENTS
GTI
POINTING
RESPONSE	EFF_AREA	POINT-LIKE	AEFF_2D
			AEFF_2D_RECO
		FULL-ENCLOSURE	AEFF_2D
			AEFF_2D_RECO
	EDISP	POINT-LIKE	EDISP_2D
		FULL-ENCLOSURE	EDISP_2D
	RPSF	FULL-ENCLOSURE	PSF_TABLE
			PSF_3GAUSS
			PSF_KING
			PSF_GTPSF
	BKG	POINT-LIKE	BKG_2D
			BKG_3D
		FULL-ENCLOSURE	BKG_2D
			BKG_3D
INDEX	OBS
	HDU