Adjust the tracking offsets to move the image on the TV monitor.

Arguments:

PointingOffset right

The distance to move the image right on the screen, expressed as an offset measured in degrees on the sky.

PointingOffset up

The distance to move the image up on the screen, expressed as an offset measured in degrees on the sky.

Example:

Both of the the following examples would move a star image on the TV display of the optical telescope right by 3 arcseconds and down by 2 arcseconds.

Using sexagesimal notation:

  tv_offset 0:0:36, -0:0:18

or using decimal degrees notation:

  tv_offset 0.01, -0.005

Context:

To measure the free parameters of the telescope pointing model, a small optical telescope, attached rigidly to the deck-platform of the telescope, is used to see how well the telescope tracks stars. The discrepancies are then used to estimate improved pointing parameters.

During optical pointing sessions the view through the optical telescope is displayed on a TV monitor. A pointing session involves visiting a large number of bright stars, one at a time, and for each star the adjusting the azimuth and elevation tracking offsets until the star is centered on a pair of cross-hairs. The observer then hits a button to tag the next record in the data-archive. At the end of the pointing session a separate program is then used to search out these tagged records, extract the recorded azimuth and elevation tracking offsets, and fit an improved pointing model to them.

To move a star image on the screen of the TV monitor, one could in principle use the offset command to directly adjust the azimuth and elevation tracking offsets. This however is difficult, because the orientation of the display relative to the directions of increasing elevation and azimuth, changes as the deck rotates. Furthermore the required azimuth offset that is needed to move the star by a given amount on the TV display, varies with the elevation of the star being looked at. For these reasons the tv_offset command was written. It takes on the job of converting from offsets on the sky, as seen on the tv display, to azimuth and elevation offsets, taking into account the elevation of the source, and the rotation angle of the camera.

Note that In order for the tv_offset to work correctly, it needs to know the fixed orientation angle of the optical telescope relative to the deck platform. This should be configured in the startup schedule using the tv_angle command.