LBTO DIMM Operating and Software Manual
This guide was originally written by Tom Herbst and Johannes Schmidt to provide basic information to operate the DIMM and make a seeing measurement.
Please let Kellee Summers know if any of this info is currently out of date, or otherwise incorrect.
See also June-2009 Users Guide
- The DIMM computer is
dimm, accessed with the user
- The DIMM webcam is http://dimm-webcam, but for performance reasons (Java), we access it via a simple html script that just grabs the jpg.
Starting up the DIMM control software
The software consists of a GUI client and a server. The server is the process which communicates with the hardware directly and does all the work. The client side is the Graphical User Interface (GUI), which enables you to send commands to the server and provides status information.
Go to a free desktop on your linux machine and open a terminal window.
In the server window type the following
ssh -X dimmuser@dimm
this script will kill any clients/servers running and start both in the background.
The client GUI should look something like this. This sample picture shows the DIMM after startup, connected to the camera and mount, before acquiring or making measurements.
Click the Start Auto-Acquire
to start the auto-acquisition thread:
The auto-acquisition thread checks every 10 seconds for whether the LBT is on-source.
When LBT goes on-source, the acquisition thread will:
- slew the mount to the first star in the current DIMM list (sorted by a combination of magnitude and distance to LBT)
- grab the web image and centroid
- slew the mount to move to the star
- repeat the grab-centroid-slew until within a configured threshold
- start measuring
The acquisition thread stops if it cannot centroid after trying a configurable number of stars. So, it may need to be restarted, via the button on the GUI.
Manually acquiring to make a seeing measurement
If you want to do a manual acquisition, use the following procedure. But, if you're using the auto-acquisition, this section is unnecessary.
The mount and camera should connect on startup. If you need to manually connect, click the connect button for the camera and mount. The camera takes a while (~30 seconds), you can watch the server terminal window for more details. The mount should not take too long as it connects to the bisque mount and then goes to its home position aligned with the LBT. If the mount was powered off, it takes longer, because it first goes to the manufacturer's home position and then back to then to the LBT alignment (you can watch it in the webcam, if you like).
Open the move mount dialog shown below by clicking on the Go to / Move button in the mount toolbar.
This dialog shows the current pointing of the DIMM in RA-Dec, Az-El, Up-Down/Left-Right and the axis rates. To go to a star simply click on one of the first stars in the list view (they are ordered by visual magnitude and distance to zenith), which has no negative Declination (I'm sorry, but I didn't have the time to fix this pointing problem) and then click on the "Go To" button below. This will send the DIMM to this star.
The pointing of the DIMM is not perfect (would be nice to have a pointing model some day) and therefore the stars are usually right at the edge of the field of view (FOV) of the camera.
Therefore, you have two options now to bring the star into the center of the FOV
Use the webcam and the "target folio" to bring it in the FOV.
Open a browser and go to the webcam via the file dimm.html
(should be a bookmark in the browser). The file contents are attached below.
Put the "target folio" over your screen and match the corners to the gray area around the webcam image in your browser. The small square in the middle matches the FOV.
Depending how far the star is away from the FOV set the moving speed (close: 4x, far: 32x) and use the arrow buttons to move the star into the square. Note:
Don't worry to get it perfectly into the center, the measurement loop will put it there.
Use the "Spiral Search" to bring the star into the FOV
Hit the "Spiral Search" button in the mount move dialog and the mount will start to search (you can watch it in the webcam for fun). If everything works fine, the spiral search will put out a message in the log of the main window and indicates that it found a star. Otherwise, there will be an error message and you should try the other approach or go to a new star.
In the main window click the "Camera Preview" button to make sure that the star is in the field of view and also check, if the tracking is on ("tracking" button should have a red line through it).
Start the measurements by clicking on the "Start measurement" button in the main window. This will set the exposure time and the region-of-interest in the camera and start the measurement loop. For the first seeing it takes about 10 seconds to fill up the image buffer for the statistical calculations. Then you should see the current seeing value int the main window and the camera preview should look like this.
The green circles indicate that the star was found in the image frame.
Watch the "Dropped Frames" field in the main window. It tells you how many frames out of the total frame number (currently 300) were dropped, because no two stars were found. If this ratio gets close to 100 %, i.e. if the stars move out of the FOV, then the measurement cycle will stop.
Saving FITS Images
There is a "Save FITS" button on the Camera Settings GUI which will dump the current buffer of image data to FITS files for a particular seeing measurement. It will save the 300 images associated with the next seeing measurement to the directory:
. (Assuming the software was started in the /home/dimmuser/restart directory like normal.) It has to be triggered for each set of images to be saved.
Focus control causes the distance between the stars to change - lower spreads the stars further apart, higher values bring the stars closer together, even causing them to cross. In general, the focus should NOT be modified because it DOES affect the seeing measurement. Just focusing to get the "best" seeing value is not correct.
The focuser is available from the GUI pulldown
- the connect button doesn't change to "disconnect" when you're connected, it just performs whatever action it should - if you're disconnected, it connects; if you're already connected, it disconnects.
buttons behave correctly now - it will not
stop until the operator pushes
. When in doubt, press
. The setting of an entered value does work, but it sometimes doesn't get there exactly. The slider bar of the
GUI should be used with extreme care - its range is 0 to 2020, so it's very
for some of the troubleshooting notes available.
Always check with the
to make sure DIMM is communicating to the shared memory. Or check the
GUI to make sure the value is getting through.