FRAME definition
Keywords: astro

Next: Plotting sun avoidance region Up: Plotting object positions Previous: Plotting object positions Contents

## `FRAME` definition

The plotting frame is defined by the command `FRAME`. The frame may be in Equatorial coordinates (Righ Ascension-Declination) or in Horizontal coordinates (Azimuth-Elevation, as seen from the seleted observatory and at the time defined by the `TIME` command). These twe modes are selected by `FRAME EQ` or `FRAME HO` respectively.

The plotting may be done in rectangular coordinates using `FRAME HO` or `FRAME EQ`, with no other argument. If other arguments are given, a stereographic projection is used, which gives a better representation of the sky (distorsion of shapes is not too serious, but the scale of the map changes from the center of the projection to the edges). The projection is defined by its center coordinates and its size: for instance
`FRAME EQ ra dec size`
will use a projection centered in the requested direction, while the size parameter, in degrees, specify the plotting range (default is 180 degrees, i.e. a whole hemisphere). Similarly,

`FRAME HO az el size`

will produce a plot centered at the requested Azimuth and Elevation (in degrees). Caution: there are two possible azimuth definitions, depending on whether the azimuth is set to zero in the North or South direction. The `SET AZIMUTH NORTH|SOUTH` command allows one to select one or the other convention.

Use of SIC variables is allowed to select frames such as

`FRAME EQ RA*12/PI DEC*180/PI 45`

which selects a frame of size 45 degrees, in equatorial coordinates, centered on the last computed object position. A few short cuts are available to produce a number of useful, classical plots:

- `FRAME HO ZENITH` gives the whole sky above the horizon, centered on the zenith position. It is equivalent to `FRAME HO 0 90 180` in the `SET AZIMUTH SOUTH` convention, or `FRAME HO 180 90 180` in the `SET AZIMUTH NORTH` convention.
- `FRAME HO SOUTH` gives the visible sky above the southern horizon. It is equivalent to `FRAME HO 0 60 120` in the `SET AZIMUTH SOUTH` convention, or `FRAME HO 180 60 120` in the `SET AZIMUTH NORTH` convention.
- `FRAME HO NORTH|EAST|WEST` are also possible, to plot the visible sky above the north, east, and west horizon respectively.

Next: Plotting sun avoidance region Up: Plotting object positions Previous: Plotting object positions Contents