Before calling any of the utilities, GKS must be open and at least one workstation open and active. This can be done with the following sequence of GKS calls:
where LUERR is a Fortran logical unit to which messages resulting from GKS internal errors may be written (unit 6 is recommended on all operating systems used by Starlink), IWKID is a workstation identifier (any integer you care to choose) and IWTYPE and ICONID are the workstation type and connection identifier respectively.
A more friendly user interface can be provided if, instead of asking the user for a GKS workstation type and connection identifier, a GNS workstation name is used (i.e. as used by SGS). A GNS name can be translated to its GKS equivalent by the GNS (SUN/57) call
where STATUS is the inherited status (returned SAI__OK if the translation is successful). More information on workstation names can be found in SUN/57.
If you wish to do any plotting with SGS routines, SGS_OPEN must be used to open GKS and the workstation. SGS makes the entire display surface of a workstation available for plotting, which in general means that part of the normalized device co-ordinate unit square will not be visible. Since the default behaviour of the NCAR utilities is to use the whole of the NDC unit square, using them becomes a little more complicated. This is discussed further in the section on co-ordinate systems (i.e. §4).
When plotting is complete, GKS must be closed down with either:
or
as appropriate.