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C00002 00002 TOP LEVEL GEM STRUCTURE
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TOP LEVEL GEM STRUCTURE
The top level of the GEM data structure is constructed out
of six kinds of nodes: UNIVERSE, WORLD, IMAGE, WINDOW, CAMERA and
LAMP; by way of contrast the polyhedron data structure consists of
BODY, FACE, EDGE, and VERTEX nodes; and the auxillary nodes are
classified as EMPTY, FRAME, XNODE, YNODE and ZNODE. Initially there
is no image node and only one Universe, World, Window, Camera and
Lamp Node. The approximate interconnections of the nodes is:
←← UNIVERSE →→
/ ↓ \
/ empty nodes \
worlds displays
↓ ↓
↓ windows
↓ ↓
lamps ←←←← WORLD →→→→ cameras ←←←← WINDOW
↓ ↓ ↓
LAMP ↓ CAMERA
↓ / \
↓ synthetic perceived
↓ images images
↓ ↓ ↓
↓ ↓ ↓
↓ ↓ ↓
3D bodies "2D" bodies
↓ ↓
faces, edges and vertices.
Now for the casual definitions of the SIX top nodes. The
Universe node is unique and all nodes are connected to it so that it
serves as an OBLIST node. The GEM universe is the mental universe or
universe of discourse for geometric modeling. Immediately below the
universe node is a ring of world nodes and a ring or displays (and a
list of empty nodes). A world node is for representing one physics
like world at a particular moment in time; three kinds of worlds
might include a perceived here-and-now world or map; a desired or
goal world; and a world of prototype platonic forms, or dictionary
world. The world points immediately at a ring of light sources
(lamps), a ring of physical camera models, and a ring of bodies.