DESI-0347

Summary:

Focal plane distortion maps. ECSV files may also be present.

Naming Convention:

DESI-0347_random_offset_{N}.fits, where {N} is the (arbitrary) number of the random realization.

Regex:

DESI-0347_random_offset_[0-9]+\.fits

File Type:

FITS, 525 KB

Contents

Number	EXTNAME	Type	Contents
HDU0	PRIMARY	IMAGE	Empty
HDU1	XOFFSET	IMAGE	2D image of x-offsets on the focal plane
HDU2	YOFFSET	IMAGE	2D image of y-offsets on the focal plane

TODO: expand description with links to documentation about how this is used.

FITS Header Units

HDU0

EXTNAME = PRIMARY

Required Header Keywords

KEY	Example Value	Type	Comment
SEED	1	int

Empty HDU.

HDU1

EXTNAME = XOFFSET

2D image of x-offsets on the focal plane.

Required Header Keywords

KEY	Example Value	Type	Comment
NAXIS1	256	int
NAXIS2	256	int
WCSAXES	2	int	Number of coordinate axes
CRPIX1	128.5	float	Pixel coordinate of reference point
CRPIX2	128.5	float	Pixel coordinate of reference point
CDELT1	0.0125	float	Coordinate increment at reference point
CDELT2	0.0125	float	Coordinate increment at reference point
CTYPE1	x	str	Coordinate type code
CTYPE2	y	str	Coordinate type code
CRVAL1	0.0	float	Coordinate value at reference point
CRVAL2	0.0	float	Coordinate value at reference point
LATPOLE	90.0	float	[deg] Native latitude of celestial pole
BUNIT	um	str
EXTNAME	XOFFSET	str	extension name

Data: FITS image [float32, 256x256]

HDU2

EXTNAME = YOFFSET

2D image of x-offsets on the focal plane.

Required Header Keywords

KEY	Example Value	Type	Comment
NAXIS1	256	int
NAXIS2	256	int
WCSAXES	2	int	Number of coordinate axes
CRPIX1	128.5	float	Pixel coordinate of reference point
CRPIX2	128.5	float	Pixel coordinate of reference point
CDELT1	0.0125	float	Coordinate increment at reference point
CDELT2	0.0125	float	Coordinate increment at reference point
CTYPE1	x	str	Coordinate type code
CTYPE2	y	str	Coordinate type code
CRVAL1	0.0	float	Coordinate value at reference point
CRVAL2	0.0	float	Coordinate value at reference point
LATPOLE	90.0	float	[deg] Native latitude of celestial pole
BUNIT	um	str
EXTNAME	YOFFSET	str	extension name

Data: FITS image [float32, 256x256]

Notes and Examples

The ECSV files express blur and offset calculated from ray-tracing (?) the DESI optical path.