The "compass roses" provide an indication of relevant coordinate systems on both guider and instrument images. The current incarnation is called "tkrose," as it is based on tcl/tk. Coordinate systems shown are (North, East), (azimuth, elevation), and optionally (XIM, YIM), the latter being the rotator coordinate frame. (See KSD 40 for details on various coordinate systems.)
It is important to understand what the "instrument frame" means. In general there are several possible vectors of interest in an instrument: "up" on the detector, "up" or "right" along the slit, and the guider-to-science detector vector. One of these is chosen as the fiducial vector, and this is represented by the "SKYPA" on FACSUM , for example. Other interesting vectors are related to the fiducial vector, usually by a constant.
A typical compass rose is shown below:
This is a rose relevant for the science instrument; note the "(i)" in the title bar. The (North, East) directions in the instrument frame are shown on the left, while the telescope's (azimuth, elevation) coordinate system displays on the right. A guider rose would show "(g)" in the title bar.
Also shown in the title bar is an indication of the "SKYPA" and "physical" position angles: "PA -0.00" indicates that astronomical p.a. of 0° (i.e. North) will be up in the instrument frame, and "V 70.69" indicates that this will correspond to 70.69° in the (az, el) frame.
The optional (XIM, YIM) frame adds this rotator frame of reference to the rose:
This is usually useful only to the OAs and possibly to engineering runs. Hence it is not supplied by default for observing.
Normally observers will not need to know how to bring up a compass rose from the command line. The guider rose is usually brought up automatically with the guider eavesdrop display, and both guider and instrument roses should also be available on a pull-down menu. The following section is more to remind the creators of those pull-down menus of the format.
First you must find the relevant version of tkrose, and determine whether it is already in your PATH or not. Assuming it is, the various calling formats are:
|tkrose -k2 &||
produces a guider rose relevant for Keck 2.
(To produce roses for Keck 1, use "-k1" rather than "-k2".)
|tkrose -k2 -i &||produces an instrument rose.||tkrose -k2 -ximyim &||produces a guider rose with (XIM, YIM) coordinates.||tkrose -k2 -i -ximyim &||produces an instrument rose with (XIM, YIM) coordinates.||tkrose -k1 -b &||produces an instrument rose with coordinates rotated 90 degrees. This is usefull for the LRIS blue side camera which is rotated 90 relative to the red side.|