The FIBGUIDER functionality needs to be tested on Technical and Service nights.
Please send us (PS, JT) your feedback.
In order to test the system, you really need to use only a few commands.
SWITCHING BETWEEN OLD and NEW SYSTEMS
In the testing phase, it will be possible to activate/deactivate the
fibguider through a simple sequencer command.
- To activate the fibguider system: setup-fibguider-on
- To deactivate and return to old system: setup-fibguider-off
Once the system is running, you really need to use only a few commands.
In case the guider is not centering properly, for whatever reason,
and you want to open the guide loop, i.e. to not give telescope offsets:
In case the system is doing a good job, and the telescope offsets (see
green talker messages) are fine, then you just do nothing at all.
To close the loop again, e.g. for the next star, use
In case you want to accept the suggested fiber position, i.e. the blue cross,
as the new reference position, i.e. green cross, use
In case you want to update the green-cross position manually, use
The fibguider uses the target's position on the StanCam fibmovie
images to tweak the telescope position. In principle the fibguider
works with and without the main guiding system, but the movie and
guiding frequency is too low to do proper guiding on its own. So in
its normal operation, the fibguider provides a secondary guiding loop,
that corrects the main NOT guiding system.
Secondly, the fibguider speeds up target acquisition, as a high-gain
telescope correction is done on the first image of an acquisition
FIBER GUIDING ROUTINE
Once the fibguider system has been activated, every fibmovie image
will be analyzed by the fibguider and the results overlayed on the DS9
image. The initial acquisition of the target in direct StanCam
imaging mode remains the same, but once the pickoff mirror has moved
to FIES (aka split position) and the first fibmovie image arrives, the
fibguider will be working the following way:
1'st image: fibguider will find the brightest target in the FOV and apply
one single offset to bring the target onto the fiber.
2-11'th images: The fibguider will be working with a very low gain, meaning
that any offsets are hardly corrected for. The reason for this becomes
clear(er) below, but basically at this moment of time the fiber position is yet
undetermined and could be wrong with some few pixels. Setting a low gain allows
the user to correct for this offset using the orange cursor keys without the
fibguider pulling the star away again. It may be possible already at this early
stage to redetermine the fiber position manually (see below).
11'th image onwards: The fibguider parameters are set to the defaults (see
below) which gives a well-behaved guiding. The fibguider will also after every
incoming image make an analysis of the last 10 images to determine the fiber
center. The suggested fiber center will not be applied automatic, only
displayed on the DS9 image. It is up to the user to decide whether to use the
computed center or not. The command to use for adopting the computed fiber
center as the new reference is fibpos-update
Similar to quickspec, a configuration file is used to set certain parameters
of the fibguider routine. The sequencer script is fibguide-config, and
called without any parameters will list the current config, for instance
tc=60, gain=0.5, guider=enabled, analyzer=enabled, outermask=big hicut=auto
- tc: Time constant in seconds used in the low-pass filter applied to the
offset. Keep at recommended value of 60 seconds for now. Be aware that no
actual telescope offsets are applied faster than this number.
- gain: The percentage of the offset value that is actually transmitted to
the TCS for teloffset. 0.5 seems a good value.
- outermask: Circle on the DS9 image which limits the analysis region, useful
in case the image got more than one object visible. Values can be big,small or
- hicut: The hicut value on the DS9 image can be set automatic based on the
image analysis. auto or manual
- analyzer: Always keep enabled! Disabling will disable image display!
- guider: Apply the offsets to the TCS, or run the fibguider in 'open loop'
mode. There are circumstances in which the fibguider will not produce useful
results, such as having multiple objects within the circle described by the
outermask, in which case the only sensible thing to do is to disable the
fibguider (fibguide-config guider=disabled) and observe with normal
FIBER POSITION ROUTINES
If the above mentioned fiber-position determination routine suggests a
reasonable improvement for the fiber position, you can accept the
suggestion by simply using
The fiber-position determination routine can also be invoked
on the command line by running the sequencer script
fibpos-compute [filename] [fiber] [no_images_to_analyze]
which by being supplied with the above parameters
will run in an interactive mode, bringing up a plot of the fiber position
analysis. And then the fiber position can be set totally manually, through an
imexam session of the loaded image, by executing fibpos-man [fiber]. In
case the fiber positions are completely messed up, some approximate default
values can be set by executing fibpos-snafu
The fibguider will make several region plots onto the DS9 display which need
to be understood:
- Green Cross: Reference fiber position. Offsets
are calculate and applied
with respect to this point. Hence, this cross should always indicate the actual
center of the fiber.
- Green Circle: The outermask circle, outside
which the image analysis will not take place.
- Blue Cross: Calculated fiber position, based on
last 10 images. Blue cross will not be present until after the 11'th fibmovie
image. From this moment onwards, the cross will update after every incoming
image. Issuing the fibpos-update command will convert the last computed
value to new reference value.
- Red X: The calculated centroid of the object,
based on the PyGuide rountine. A new centroid is calculated for each incoming
image. In case no centroid can be calculated (too faint, too cloudy, too much
down in fiber), no X will be shown.
Keep an eye on the Talker. All important information about the fibguider is
- You know the fibguiding is doing well when all markings fall on top of
each other and that that point corresponds to the true fiber center as seen
on the DS9.
- When the computed fiber position (blue cross) consistently are offset with
respect to the reference position (green cross), and this new position seems to
better reflect the fiber center, it's time to update the fiber position with
- Be patient. The system is designed to react slow and conservative. Last
thing we want is actually pulling the star away from the fiber.