guide Program

NAME

guide - causes the guider to operate

SYNOPSIS

guide

time= [exptime=]
[nooffset] [pid=] [tv[=span]] [logid=] [bin=] [box=]
[minsum=] [minoff=] [gain=] [integral=] [delay=]
[debug[=]]

DESCRIPTION

guide starts the guider to operate once the telescope has been positioned, the xy stage placed in the right place (see guidestar and the guide star centered (see acquire) on the guider CCD. This program reads the guider camera, computes the centroid of the guide star image and then moves the telescope to keep the image centered.

The guider operates in the following manner:

takes guider image
subtracts dark
subtracts sky value
finds modified (see below) centroid
if centroid is lousy, exits
calculates offset
multiplies by linear
multiplies displacement sum by integral and adds to offset
adds fudge to ra (if offset > minoff)
if offset is greater than minoff offsets the telescope
loops

The program is way too complex for manual use due to the large number of parameters, but should be run via a script.

The program traps the first Cntrl^C key and will terminate when the exposure is made.

OPTIONS

time= specifies the overall operation time for the guider. This option must be specified. It calculates an integer number of cycles by dividing this time by the exposure time.

bin= changes the binning factor from the default of 4. These feature has never been tested.

box= changes the size of the guiding box in pixels from the default 25 on a side. The centroid is evaluated with this box. It is shown on the TV display.

delay= sleep time in integer seconds after offset.

gain= - sets the factor that the calculated offset is used to correct the real offset. The default value is 1.0.

integral= - sets the factor that the total summed offset is used to send to the telescope. The default value is 0.

logid= - if set to non-zero sets the database record that will be updated with the guiding statistics.

minsum= - sets the minimum star intensity that is needed to operate. If it falls below the program exits. The default value is 500 (check with program).

minoff= - sets the minimum offset distance in arc-seconds that is transmitted to the telescope. The default value is 0.

nooffset if you specify this option it operates as above, but without actually offsetting the telescope.

pid= sets the process ID of the calling process and if the calling process is no more, guide will die.

time= overrides the default exposure time of xx seconds.

tv - specify this if you are running under X-windows and want to watch the guider images. The image span is set by default but can be changed by setting tv= the desired span.

NOTES

The file gdarkN.fits where N is the time in seconds must be found in the directory that the guider is operating in. If it doesn't exist, you can create with the gdark script.

The modified centroid uses on the part of the image that is greater than zero to compute the centroid. The signal is computed by all parts of the image.

Program index