Change the tracking offsets.

Optional qualifier arguments:

/add

If this modifier is present the offsets will be added to the existing offsets. Otherwise they will replace them.

Mandatory arguments:

(none)

Optional Arguments:

Double az

An offset to be added to the mount azimuth.

Double el

An offset to be added to the mount elevation.

Double ra

An offset to be added to the Right Ascension of celestial sources, as they are being tracked.

Double dec

An offset to be added to the declination of celestial sources, as they are being tracked.

Double y

An offset towards the zenith, directed along the great circle that connects the un-offset pointing center and the zenith.

Double x

An offset along the great circle that is both perpendicular to the above described y axis and passes through the un-offset pointing center. When the telescope is pointing south, y increases towards the west.

Examples:

The following example adds an additional 10 arcseconds to the pointing offset of the azimuth, and 0.02 degrees to the offset of the elevation axis.

  offset/add az=0:0:10, el=0.02

The following example adds 10 arcseconds to the geocentric apparent declination of the source that is being tracked, and to subsequently tracked sources.

  offset dec=0:0:10

Context:

Azimuth and elevation tracking offsets

The azimuth and elevation tracking offsets are added to the mount azimuth and elevation that are the output of the pointing model.

Equatorial tracking offsets

The Right Ascension and Declination offsets are added to the apparent geocentric equatorial coordinates of the source before the pointing model is applied to determine

Sky tracking offsets

Sky offsets are angular offsets on the sky relative to the output azimuth and elevation of the pointing model. The Y sky offset is the same as an elevation offset. However the X sky offset differs significantly from an azimuth offset, in that the distance that it moves the pointing center on the sky, does not depend on the telescope elevation, and is always orthogonal on the sky to the direction of the Y axis offset. This makes sky offsets ideal for mapping out the beam of the telescope.

Sky offsets are implemented by defining a spherical coordinate system on the sky whose origin is the source position, such that X and Y lie along two orthogonal great circles that cross at the source position. The Y-axis great circle follows the line of increasing elevation, and the X-axis great circle is perpendicular to this.

A way to better understand sky offsets, is to imagine lying on one's back, at the center of the dish of the telescope, with one's feet pointed towards the lowest part of the dish, the top of one's head pointed towards the highest part of the dish, and one's arms stretched out perpendicularly from one's sides, flat against the dish. One's feet would then point at a sky offset of x=0,y=-90 degrees, one's head would be pointed at a sky offset of x=0,y=90, one's right hand would point at a sky offset of x=90,y=0 degrees, one's left hand would be pointed at a sky offset of x=-90,y=0.

Note that sky offsets are applied before azimuth and elevation tracking offsets.