Index
rotcor [state=on|off, limit=?, encoder_zero=?, shaft_zero=?]

Specify how and if the elevation rotation meters should be used.

Mandatory Arguments:
(none)
Optional Arguments:
SwitchState state
If this argument is on, then the readouts of the rotation meters on the elevation shaft and encoder body will be used to correct the pointing for the anomalous twisting of these members. If it is off then they will be ignored. In the archive the tracker.corflags register can be used to determine whether this correction was enabled.
AngleLimit limit
If the magnitude of either rotation meter readout is greater than this number, then the correction won't be made and the overflow condition will be recorded in the tracker.corflags register.
Angle encoder_zero
This can be used to specify a zero offset for the encoder-body rotation correction.
Angle shaft_zero
This can be used to specify a zero offset for the elevation-shaft rotation correction.

Example 1:
The following example enables the use of the rotation meters in the pointing model, and specifies that if the sum of the rotation meter outputs is outside of the range -100..100 arcseconds, this will be considered an error. 
 rotcor state=on, limit=0:1:40
Example 2:
The following example stops the rotation meters from being used in the pointing model, without changing any previously established correction limit. 
 rotcor state=off
Example 3:
The following example specifies zero offsets for both of the rotational corrections, 5 arcseconds for the encoder-body rotation correction, and 1 and half arcminutes for the elevation shaft correction. 
 rotcor encoder_zero=0:0:5, shaft_zero=0:1:30

Context:
As the elevation of the telescope changes, small distortions in the normally unmoving elevation shaft and the encoder mount result in an apparent rotation of the encoder shaft, thus changing the elevation readout from what it should be. Rotation meters measuring these twists can be used to correct for this effect.

To prevent a broken rotation meter from sending the telescope all over the sky, a readout limit is required.

The arbitrary zero points of the rotation meters slowly vary, so this command provides a way to specify zero offsets.

Also see the zero_rotcor command for an alternate way to set the zero offsets.

Note that the rotcor is disabled and has a limit of zero degrees and no zero offsets when the system starts. An example of a suitable limit would be about 100 arcseconds. The appropriate limit could be set in the reboot file (see load_reboot_script).

Martin Shepherd (6-Jul-2000)