The master guider display is operated by the OA. Observers generally run an ``eavesdrop'' from a menu on the instrument control software. In principle a second eavesdrop can be daisy-chained off the first, but this is rarely done because of concerns about performance, and slowing down guiding on the master display.
Normally there will be one menu item that will automatically find the master guider display no matter what computer and screen it is on. There are sometimes (not always) other options that are hard-wired for certain computer/screen combinations. Normally the observer can bring up the eavesdrop on any of the screens available to her/him.
There are several functions that can be accessed by the observer:
Circles can be superposed on the display using the mouse. Note that centroids are not calculated; the circles are simply centered at whichever pixel the cursor is on at the time.
| add fiducial | click with the middle mouse button |
| delete circle | click the right mouse button within a couple pixels of the center of an existing circle |
| delete all circles | type ``d'' on the keyboard |
Note that the distance in pixels and the angle between the last two circles formed are displayed in the informational fields at the top of the display. This can be used to quickly (and roughly) estimate a rotation to get two objects on the slit at one time, for example.
Occasionally it is useful to enlarge the pixel size displayed on the screen. The keys below perform that function and its inverse. Note that you can also grab the corner of the window and shrink it so that the window no longer contains the entire image. When you do this scroll bars will appear, allowing you to scroll around the image. This may be useful, e.g., if you are using a large, 1024x1024 guider CCD, want to see it at full resolution, but do not want to take up too much space on your screen.
Don't forget, however, that you are not viewing the entire field of view when scroll bars are displayed on the window!!
| Enlarge | type ``b'' or ``l'' on the keyboard (Think big or large.) |
| Reduce | type ``s'' on the keyboard (Think small.) |
Note: If the commands do not seem to work, try "left clicking" in the guider image display first to activate keyboard commands.
The cursor will read out the counts in each pixel if the default binning is in use. Otherwise it will display a hyphen in that space (next to the (x,y) coordinates).
While the observer cannot access these functions, it is useful to understand what the OA can do on their end. Also, the observer may, for example, want to save some guider frames for later analysis. They need to know what to tell the OA.