Specify the encoder angle that corresponds to zero topocentric angle.

Arguments:

Axes axes

The set of telescope axes to configure.

Double offset

The encoder angle when the telescope is pointing at the topocentric zero angle of the specified axis.

Example:

In the following example, the first command tells the control system that at zero degrees azimuth, the azimuth encoder actually reads 268.523 degrees. Similarly, the second commands tells it that if the telescope could be pointed at zero elevation, then the elevation encoder would actually read -141.526 degrees.

 encoder_offset az, 268.523
 encoder_offset el, -141.526

Context:

For a number of engineering reasons, telescope axis encoders are rarely installed in such a way that a zero count from an encoder corresponds to zero of the corresponding topocentric angle. Even in the few cases where this is done, it is likely that the zero points will change slightly with time. So this command is provided for indicating the encoder zero offsets to the control system. These zero offsets are generally determined by fitting a pointing model that includes them, to the observed positions of the peaks of many astronomical point sources.

Note that to ensure that this command is always sent to the control system after a reboot, invoke it once per axis in the rtc boot script, $TCS_DIR/conf/rtc.init boot script.