The guider will operate until: a) it is killed by the SIGINT (#2) or SIGTERM
(#15) signals b) it completes cycles operations or c)
maxtime has
elapsed. (Killing the guider with the -9 option will just abort it). If the
guider is unable to keep lock (i.e. the signal is below the value set by
`thresh'), it keeps on trying however, it will not move the telescope (except
when `die' is specified). At exit it will write the following statistics to
stdout and also to the XVista `gustat'
keyword.
ra_mean ra_rms dec_mean dec_rms b_mean b_rms exposure sky_mean
where the ra and dec_means are the average guide correction in arc-seconds (note to calculate the drift rate you must divide by the guide exposure; this may be impossible in auto mode). The ra_rms and dec_rms are the root mean square corrections in arc seconds. The b_mean and b_rms are the average and r.m.s. values of the stellar brightness. This value is calculated by taking the sum of the brightness over sky in the guide box and dividing by the exposure time. Note: these are rates while `thresh' specifies a total integrated over the integration time. The seventh value is the exposure time in seconds. In auto mode, it is the last value of the exposure time. The final value is the average sky rate in adus per second. Note: The values of ra_mean, ra_rms, dec_mean, and dec_rms are evaluated only for suc_cessful guide cycles. The other indices are summed regardless.
While guiding the program will issue the `dome center' message every 180 seconds to make sure that the dome slit is properly positioned.
Note: if the offset is less than 0.00009 degrees in both axes, no offset message will be transmitted (to cut down tserver chatter).
Also: if there is an error in the offset command, the guider will call the cycle a failure and try in the same manner as a loss of intensity.
time - adjusts the exposure time from the default value of 2.0 second.
window - sets the size of the box to be used for the centroid. The default value is 20.
damp - multiplies the expected offset by the damping factor (usually less than one) so the loop will converge.
maxtime - sets the maximum number of seconds that the guider will operate. In fact this number specifies an upper bound, since the program will exit if the next exposure cycles exceeds maxtime. If maxtime exceeds the exposure time then the message:
exposure time less than guide time
will be written to the gustat symbol.
no_offset - causes the guider not to send the offset commands to the telescope. This option is useful for testing.
thresh - sets the minimum total number of counts found in the guider box for the guider to operate. The default value is (1000).
cycles - set the number of guiding cycles (centroid/offset pairs) that will be executed. The default number is infinite.
sleep - causes the guider to pause for the specified number of seconds between interrogations.
die - causes the guider to stop functioning if guider fails to lock for the specified number of cycles. The program will not exit, but merely keep the dome centered and the slit open until it exits in the usual ways (see above). The failure count is cumulative. However, each failure is `redeemed' by 10 successful guide cycles. If the guider fails because of this flag the message:
guider died after xx seconds
will be written to stdout or in the GUSTAT symbol. In default operation, the guider will not exit if it cannot guide.