In general, with the following program :
CALL TDOMA2 (xmin,ymin, xmax,ymax)
CALLTSCENE (SCENID, NUMSTR,IDLIST, VIEWID)
the PSLMT and PSMCV elements are inserted in the structure SCENID and the set becomes a parameter of the PSLMT function transforms all points (X,Y) into a point (X',Y') with
X' = (X-xmin)/(xmax - xmin)
Y' = (Y-ymin)/(ymax - ymin)
and with the following program :
CALL TDOMA3 (xmin,ymin,zmin, xmax,ymax,zmax)
CALLTSCENE (SCENID, NUMSTR,IDLIST, VIEWID)
the PSLMT3 and PSMCV3 elements are inserted in the structure scene_id and the set becomes a parameter of the PSLMT3 function transforms all points (X,Y,Z) into a point (X',Y',Z') with
X' = (X-xmin)/(xmax - xmin)
Y' = (Y-ymin)/(ymax - ymin)
Z' = (Z-zmin)/(zmax - zmin)
In conclusion, if the structure SCENID is posted on a workstation with the identifier WKID, a traversal set off on WKID,transforms all points of the structures in the scene with coordinates inside the domain, into a point inside the space [0-1, 0-1, (0-1)] in WC (World Coordinate)
This is called a scene transformation
N.B. : If the domain to be transformed is not square (in 2D) or cubic (in 3D), the data is distorted during traversal by the scene transformation (the height / width ratio data is not maintained in WC). To avoid this problem, always work with a square or cubic domain which fits the given data as closely as possible.
In 2D the most practical method consists of choosing the smallest square capable of containing the data limit rectangle and with the same center :
Similarly, in 3D, the most practical method consists of choosing the smallest cube capable of containing the data limit parallelepiped, and with the same center :
Of course, the SCENID structure may be modified by PHIGS. In particular, it is possible to insert attribute functions at the start of the structure. These are then taken into account by all the primitives of all the structures in the scene. (see attribute scope )
Note that the view index attribute is positioned at the start of the SCENID structure : the view index VIEWID is therefore used by all the primitives in all the structures called by the scene.