gsurf Library

Overview

The gsurf library, consisting of approximately 20,000 lines of C code, contains some 180 public functions and about twice as many internal functions for run-time data storage, manipulation, querying, and visualization using OpenGL. The library handles all drawing and lighting operations, including use of user-defined clipping planes and drawing various style "fences" on clipping planes when drawing multiple surfaces, and treats datasets as objects which can be used for various attributes of the rendering. It allows data sharing (e.g., same data for more than one attribute of same or different surfaces), separate masking for each surface, multiple surfaces, vector sets, or point sets, and will also allow multiple volumes. The library provides all query features such as 3D "point on surface", keyframe animation routines, and full state saving functionality. Database-specific routines for interfacing with the GRASS GISlib are kept isolated for easier library reuse with other databases. The gsurf library is not dependent upon any particular interface library, and has been used successfully with both Motif and Tcl/Tk.

The library is designed to provide a unique "handle" or identifier number to the calling program for each new geographic object added to the model. The object could be a surface, vector set, or point set, which could each be defined by one or more database files. Once created, the application only needs to keep track of the "handles" to the objects (which are returned by the creation routines); for example, to draw a surface the application would make the call:

  GS_draw_surf(id)

where id is the handle number. To associate a vector set with a surface and then draw all surfaces with the vector set draped over the one selected, the application would use the calls:

  GV_select_surf(vid, sid)
  GS_alldraw_surf()
  GV_draw_vect(vid)

where vid and sid are the handles for the vector set and surface. Similarly, to query or change attributes of the object, the handle is used in conjunction with the new attribute, as in:

  GV_set_vectmode(id, mem, color, width)

Naming Conventions

The following naming conventions for function prefixes are used:

GS_
Functions which have to do with loading & manipulating surfaces. Also functions for library initialization, setting global variables, viewer positioning, and lighting.
GSU_
Utility functions for distance calculations, common 2D & 3D unit vector operations such as cross product or vector arithmetic.
GV_
Functions which have to do with loading & manipulating vector sets.
GP_
Functions which have to do with loading & manipulating point sets.
GVL_
Functions which have to do with loading & manipulating 3D volumes.
GK_
Functions which have to do with setting & manipulating keyframes for viewer position animation (fly-bys).

Programmers' documentation is currently incomplete, but see the following for more details of the library design and capabilities in the appendix:

public function prototypes
public include file gsurf.h
public include file keyframe.h
public color packing utility macros rgbpack.h
private types and defines gstypes.h
private utilities gsget.h

gsurf Library

Overview

Naming Conventions

Alphabetical Function Index Function Index by function

Alphabetical Function Index
Function Index by function