SGS is a set of subroutines for performing low-level graphics input/output. SGS is implemented above the GKS package (described in SUN/83 the RAL GKS Guide and the ISO document GKS 7.4) which is a device independent graphics system designed to be the kernel of a wide variety of graphics systems. GKS, which is very comprehensive, does not itself set out to provide the most convenient interfaces for all applications, and SGS allows easy access to many of its more straightforward features.
SGS, while preserving GKS concepts and indeed allowing direct GKS calls to be interspersed with SGS calls, is optimised for convenience in simple cases. Many of its features are low level (for example: open, draw a line, draw a text string, close), but there are some routines of a slightly higher level (drawing arcs and formatted numbers etc). SGS does not include routines for high level operations like drawing annotated axes or complete graphs.
Many plotting programs will be written entirely with SGS or higher level calls. There will, however, be occasions when GKS routines are used as well, usually because a specialised feature of GKS is needed. Therefore this user manual uses GKS concepts to describe SGS, and Appendix C describes SGS routines in terms of their effect on GKS. This will allow programmers to mix GKS and SGS calls in safety. The unadventurous user may safely ignore the appendices.
Throughout this manual the normal FORTRAN variable naming conventions are adhered to: i.e. all integers start with the letters I–N, all reals with letters A–H and O–Z. Character and logical variables have their type explicitly referenced in the text.