Processed Guider Images

This manual describes the contents of processed guider images (proc-guide). In particular this describes images with the following in the header:

SDSSFMT GPROC 1 0
                    

HDU0

The calibrated guider image—at least as calibrated as it was for processing by the guide loop. As of guiderActor v1_0_12, neither dark subtraction nor flat field correction is done, so the image is not really calibrated.

The header contains cards describing the configuration of the guide loop and some measured and applied offsets.

HDU1

The mask for the calibrated guide image. The bit planes are:

• (bit 0) saturated pixels. As of v1_0_9 no useful characterization of the camera has been done, so only 0xFFFF pixels have this set.
• (bit 1) bad pixels. Hot/dead pixels, etc. Currently none are defined.
• (bit 2) masked pixels (i.e. edge of guide probe). Not available in v1_0_9 and earlier.

HDU2

Postage stamp images for the small guide probes, where each postage stamp image has been rotated so that north is up and ???east is to the right??? Each postage stamp is square. Extra pixels (pixels around the edge that are not computed from the camera image), if any, are set to the estimated background. The full image is one tall, skinny image comprised of the postage stamps, in order of increasing probe number starting from row=y=0.

HDU3

Masks associated with the postage stamp images for the small guide probes, in the same format.

HDU4

Postage stamp images for the large guide probes, in the same basic format as HDU2.

HDU5

Masks associated with the postage stamp images for the large guide probes, in the same format.

HDU6

A binary table containing information about the guide probes and guide stars. Each entry is for one guide probe; data is listed in probe number order (starting from 1).

Column	Type	Description
exists	string	Does the guide probe exist? ("T/"F")
enabled	string	Is the guide probe enabled? ("T"/"F")
x/yFocal	float	Center of guide probe on plug plate (mm)
x/yCenter	float	Center of guide probe on image (pixels)
radius	float	Radius of guide probe active area on image (pixels)
x/yFerruleOffset	float	Offset of guide probe active area w.r.t the ferrule (mm); need more info???
rotation	float	Rotation of guide probe with respect to the plate (deg); what is the 0 point and sign???
rotStar2Sky	float	Rotation of sky with respect to the image (deg); what is the 0 point and sign???
focusOffset	float	Focus offset of guide probe in µm; + is further from the secondary (shorter ferrule)
fiber_type	string	Type of guide probe; one of: "ACQUIRE", "GUIDE", "TRITIUM"
x/ystar	float	Centroid of star on image (pixels)
dx/y	float	Centroid of star - center of guide probe on image (mm on focal plane)
dRA/dDec	float	Centroid of star - center of guide probe along RA/Dec (mm on focal plane)
fwhm	float	FWHM of star (arcsec)
poserr	float	???
stampSize	int	Index of postage stamp HDU: 1=HDU4 (small), 2=HDU4 (large), -1=none (Tritium source).
stampIdx	int	Index of postage stamp: 0 for the postage stamp starting at x=0, -1 if no postage stamp (e.g. Tritium source or possibly a guide probe that is unavailable).