NAME
dither - Command to perform a dither observation
SYNOPSIS
dither [-h] [-noverbose] [-title ``title'']
-intcount <integrations>
-secs <secs>
-waitforloop
[-offset <RA arcsecs> <DEC arcsecs>]
[-skypa <sky pa>]
[-noprobemovement]
[-nointegrations]
[-notcs]
[-noactions]
[-resume <dither point]
[-tcshost <hostname>]
[-camera <UDAS camera server name>]
[-noloopcontrol]
(-9point|-5point|-multi) (<x offset> <y offset>)+
DESCRIPTION
dither is a script executed from the command line which will
allow the observer to perform a dithered observation using
INGRID and the NAOMI adaptive optics system. Three modes of
dithering are available to the user; 5 point dither, 9 point
dither and multi point dither. In the case of the first two
modes, the observer will specify a single coordinate pair
and the script will calculate, based on the coordinate pair
specified, the necessary telescope offsets to perform a 5
and a 9 point dither pattern respectively. In the case of
the multi point dither, the observer will specify a coordi-
nate pair for each offset.
It should be noted by default, the AO loop is opened before
the telescope and the WFS pickoff probe is offset at each
dither pattern. Coordination of both the telescope and the
autoguiding probe when performing the offset is the respon-
sibility of NAOMI. The software will detect whether the AO
system is in LGS or NGS mode and control the corresponding
loop as appropriate.
After each TCS offset, the dither script will instruct
UltraDAS to execute a run before moving on to perform the
next offset and dither integration. The number of coadds to
be perform should be set before the dither sequence is
started.
The dither script takes into account the sky PA of the tele-
scope when calculating the position to move the WFS pickoff
probe during the dither sequence.
At the end of the dither sequence, the script will reset the
telescope offset.
NOTE: The type of the dither operation to be performed
should be entered as the last item on the command line.
FIVE POINT DITHER PATTERN
The observer will specify a single positive x-y offset pair
on the command line expressed as a real number in arcsecs.
The offset will be used to calculate a series of four dither
offsets which will be applied. The pattern of the dither
will be as follows;
2 5
1
3 4
NINE POINT DITHER PATTERN
The observer will specify a single positive x-y offset pair
on the command line expressed as a real number in arcsecs.
The offset will be used to calculate a series of eight
dither offsets which will be applied. The pattern of the
dither will be as follows;
2 9 8
3 1 7
4 5 6
OPTIONS
The command line options that the program accepts are
detailed below.
-h Print usage information about the application.
-offset <RA arcsecs> <DEC arcsecs>
This specifies a general offset which will be applied
to all points in the dither pattern therefore shifting
the entire dither sequence by the offset specified.
-noloopcontrol
The state of the AO loop is not changed in any way by
the dither script.
-secs <integration length>
The intended length of each integration in the dither
pattern.
-intcount <no. of integrations>
The number of integrations which are to be performed at
each dither point.
-noprobemovement
Instructs the program not to attempt to move the WFS
probe throughout a dither sequence.
-nointegrations
Request that no integrations are performed on the cam-
era server. This mode is usually used for testing only.
-camera <UDAS Camera Server>
The name of the UDAS camera server associated with the
detector that the integration is to be performed upon.
If not specified, the default is NAOMI.
-waitforloop
Instructs the script to wait between dither points
until the user has confirmed that it is clear to
proceed.
-skypa <skypa>
Normally the application attempts to establish the
current sky PA from the TCS. This option allows the
user to specify the Sky PA manually from the command
line. The Sky PA should be expressed in degrees. Note
that whatever the user specifies on the command line
overrides the Sky PA returned by the TCS. -resume
<dither point> Instructs the application to resume
dithering at the dither point specified. The previous
dither points in the pattern up until the dither point
specified are ignored.
-notcs
Indicates that the telescope is not to be moved during
the dither sequence.
-noactions
Indicates that there will be no interaction with any
external agents whilst the dither script is run. This
is to say that there will be no loop control, no tele-
scope movements, no pickoff movement and no integra-
tions taken.
-title
The title to be associated with each run of the dither
pattern. Note that the title should be enclosed in dou-
ble quotes. If no title is specified, the default title
in the TCS catalogue will be used. By default, the
title of the integration will be prefixed with the pat-
tern Dx/y where x is the dither point reached and y is
the number of dither points in this sequence.
-5point <x offset> <y offset>
Execute a five point dither with the requested offsets
specified in arcsecs and expressed as positive real
numbers. This option should be specified at the end of
the command line arguments. The coordinate pair that is
specified will be used to calculate the four dither
offsets around the origin. This option must be speci-
fied as the final command argument.
-9point <x offset> <y offset>
Execute a nine point dither with the requested offsets
specified in arcsecs and expressed as positive real
numbers. This option should be specified at the end of
the command line arguments. The coordinate pair that is
specified will be used to calculate the eight dither
offsets around the origin. This option must be speci-
fied as the final command argument.
-multi (<x offset> <y offset>)+
Execute a user defined dither pattern where each dither
offset is specified by the observer on the command
line. -The multi option should be specified as the last
argument on the command line. Following the -multi
option should be a list of coordinate pairs expressed
as real numbers which represent in arcsecs, the offsets
from the origin at which to perform a dither observa-
tion. There are no constraints on the number of dither
offsets that may be specified. This option must be
specified as the final command argument. Note that when
specifying the dither points it is not necessary to
specify the first dither point (0,0) as this is
automatically included in the sequence by the script.
-noverbose
Instructs the script not to produce verbose output
about it's execution.
RETURN VALUES
The script returns the following codes after execution.
0 - Script completed without problem
This code is returned when the script runs successfully
to completion.
1 - Command Failed
This code is returned when the command is fails.
Failure may be due to a number of reasons and which
will be reported to both stdout and to the syslog.
2 - Command timed out
The command has failed to complete in the allocated
time allowed.
3 - The integration time has not been specified correctly
This code is returned if the observer has omitted to
specify the length of the integration correctly using
the -secs option.
4 - The dither type has not been declared correctly
This code is returned when the observer fails to
specify the type of the dither operation correctly. It
may also be returned when the observer does not
correctly specify the dither offsets.
5 - Unable to instruct NAOMI to offset telescope
The script encountered problems when attempting to
instruct NAOMI to offset the telescope.
6 - Unable to instruct UltraDAS to perform a run
The script encountered problems when attempting to
instruct UltraDAS to execute a run.
20 - No command status returned by the NAOMI sequencer
No command status has been returned by the NAOMI
sequencer so it is impossible to deduce the status of
the NAOMI command.
ENVIRONMENT
NAOMIHOST
If the NAOMIHOST environment variable is set, this will
be used by the script to establish the location of the
NAOMI data server. The NAOMI data server is used by the
script in order to command NAOMI thus the script must
know which machine upon which to find it. By default,
the NAOMI data server is expected to be found on the
navis.ing.iac.es. See EPMDataServer(1) for more infor-
mation.
TCLLIBPATH
This should be set to include the directories which
contain the WHT OCS support classes. This is done by
default from the whtobs account.
SEE ALSO
EPMDataServer(1)
AUTHOR
Craige Bevil (cb@ing.iac.es)
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