ARC

Draw an arc of an ellipse

Description:

A specified arc of an ellipse is drawn from the position angles of the start and end of the arc, the semi axes, the position of the centre and the rotation of the axes. If no parameters are specified then whole ellipses can be drawn from the data stored in the following data areas:

Usage:

arc [a] [b] [x0] [y0] [pastart] [paend] [rotation]

Parameters:

A = _REAL (Read and Write)
The semi-major axis of the ellipse.

If no value is specified on the command line, the current value is used. If there is no current value, a default value 1.0 is used.

B = _REAL (Read and Write)
The semi-minor axis of the ellipse.

If no value is specified on the command line, the current value is used. If there is no current value, a default value 1.0 is used.

X0 = _DOUBLE (Read and Write)
The X coordinate of the centre of the ellipse.

If no value is specified on the command line, the current value is used. If there is no current value, a default value 0.0 is used.

Y0 = _DOUBLE (Read and Write)
The Y coordinate of the centre of the ellipse.

If no value is specified on the command line, the current value is used. If there is no current value, a default value 0.0 is used.

PASTART = _REAL (Read and Write)
The position angle of the start of the arc (degrees).

If no value is specified on the command line, the current value is used. If there is no current value, a default value 0.0 is used.

PAEND = _REAL (Read and Write)
The position angle of the end of the arc (degrees).

If no value is specified on the command line, the current value is used. If there is no current value, a default value 360.0 is used.

ROTATION = _REAL (Read and Write)
The angle that the major axis makes with the horizontal (degrees anti-clockwise).

If no value is specified on the command line, the current value is used. If there is no current value, a default value 0.0 is used.

FROMDATA = _LOGICAL (Read)
If TRUE, the command will use the data already loaded to draw whole ellipses, with positions and sizes specified as above. [FALSE]
PROJECTION = _CHAR (Read)
The geometry that is to be used to plot the arc. This is explained in detail in the section on projections. Allowed values: "NONE", "TAN", "SIN", "ARC", "GLS", "AITOFF", "MERCATOR" and "STG".

This parameter is not specified on the command line. If no value is specified on the command line, the current value is used. If there is no current value, a default value "NONE" is used.

RACENTRE = _CHAR (Read)
The centre of the projection in RA (i.e. the angle must be specified as hh:mm:ss.sss). This parameter is only required for PROJECTION values other than "NONE".

This parameter is not specified on the command line. The value of the global parameter PONGO_RACENTRE is used. If PONGO_RACENTRE is not defined, the default value "0" is used.

DECCENTRE = _CHAR (Read)
The centre of the projection in declination (i.e. the angle must be specified as dd:mm:ss.sss). This parameter is only required for PROJECTION values other than "NONE".

This parameter is not specified on the command line. The value of the global parameter PONGO_DECCENTRE is used. If PONGO_DECCENTRE is not defined, the default value "0" is used.

ERSCALE = _REAL (Read and Write)
The factor used to scale values in the EXCOL and EYCOL data areas. This allows the ellipse axes lengths to be scaled, changing the sizes of ellipses produced using the FROMFILE parameter.

This parameter is not specified on the command line. The value of the global parameter PONGO_ERSCALE is used. If PONGO_ERSCALE is not defined, the default value 1.0 is used.

Examples:

PONGO > ARC 1 1 0 0
will draw a circle of radius 1 (world coordinates), assuming the PASTART and PAEND parameters have their default values (0.0 and 360.0 degrees respectively).
PONGO > ARC FROMDATA
Draws arcs using the information read into the XCOL YCOL EXCOL and EYCOL data areas.