SIZE1, SIZE2 and SIZE3

Expressions defining the size of each symbol. The values are (more or less; see below) normal CURSA expressions involving columns in the targets list (see Appendix ). Most symbols (see Table ) require only one size to be specified. This simple size is always given by SIZE1. However, the openellipse and filledellipse symbols require three values to define the ellipse. Here SIZE1 is the semi-major axis, SIZE2 the semi-minor axis and SIZE3 the position angle. SIZE1 and SIZE2 should evaluate to a value with the units specified by the UNITS item above. However, the SIZE3 should always be a position angle in degrees, measured eastwards from north, following the usual convention.

The following two functions were added to assist in calculating sizes for columns such as magnitudes or flux which are not naturally angular extents and need to be scaled to produce a symbol size.

scale(column, colmin, colmax, smin, smax)

 
Performs a simple linear scaling. column is the name of the column to be scaled. colmin and colmax are the minimum and maximum values in the column to be scaled. If a value of the column, $V_{c}$, lies within the range colmin to colmax, then the scaled value returned, $V_{s}$, is computed using the formula:

$$V_{s} = {\tt smin} + (V_{c} - {\tt colmin}) . \frac{({\tt smax} - {\tt smin} ) }{({\tt colmax} - {\tt colmin} ) }$$ (6)

If $V_{c}$ is larger than colmax then colmax is returned; if it is smaller than colmin then colmin is returned. smin and smax are the largest and smallest values of the plotting symbol, expressed in the units of UNITS. To accommodate quantities such as magnitudes which increase `the wrong way round' simply flip the values for smin and smax.

ascale(column, smin, smax)

 
(auto-scale) is similar to scale, but the scaling is defined by the minimum and maximum values of the column.