LABEL

The name of the column to be used to label each object.

If the graphics translation file simply consists of a set of specifiers for the above items they will be applied to all the objects in the list. Often this approach will be adequate. However, sometimes it will be desired to plot different objects in different ways (for example with different symbols or colours), depending on whether or not they meet some criteria. This behaviour is achieved by enclosing the definitions for the graphics attributes within a set of clauses, where each clause defines some aspect of the symbol to be used for objects which meet the criteria. The syntax is:

IF condition

  $\vdots$

ELSE IF condition

  $\vdots$

ELSE IF condition

  $\vdots$

ELSE

  $\vdots$

END IF

condition is the condition, expressed in terms of columns in the targets list, which objects must satisfy to be plotted in the particular way. An example might be `MAG .LT. 12.0' to plot objects brighter than 12th magnitude in a given way. The following points apply.

• An arbitrary number of clauses are permitted; there is no upper limit.

• The optional ELSE is a special clause which is applied to any objects in the targets list which do not satisfy any of the other cases. There is no condition attached to ELSE. If ELSE is omitted then objects which satisfy none of the cases are not written to the output target list (and hence are not plotted).

• Because the conditions defining the set of objects to be included in each case are not necessarily mutually exclusive it is technically possible for a given object to match more than one case. In this event it will be plotted in the manner prescribed by the first case it matches.

• Any graphics attributes defined outside an IF ...END IF apply to all the objects plotted.

• An arbitrary number of separate IF ...END IF constructs can be included in the graphics translation file. Typically, more than one might be used to set up different aspects of the plotting symbol (for example, one construct to set the plotting colour, based on the photometric colour of the object and a second to set the symbol shape based on the object classification).

• However, IF ...END IF constructs may not be nested.

• The two words `ELSE IF' may be separated by zero, one or an arbitrary number of spaces; similarly the two words `END IF' may be separated by zero, one or an arbitrary number of spaces.

• The LABEL item cannot appear inside a clause. If present it must be outside any clauses and refers to the entire target list.