## 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.