The preamble is of the following form:
##G4.PRIM-FORMAT-2.4 /BoundingBox xmin ymin zmin xmax ymax zmax !SetCamera !OpenDevice
The first line of a g4.prim-format data must be the header-comment line
as ``##G4.PRIM-FORMAT-2.4''.
The line, /BoundingBox ...
defines a bounding box which determines extension of the described 3D scene.
Real numbers xmin, ymin and zmin are minimum
x, y, and z world coordinates of the 3D scene,
while xmax, ymax and zmax are maximum.
DAWN uses this information for automatic camera positioning,
automatic drawing of coordinate axes, etc.
Example:
##G4.PRIM-FORMAT-2.4 /BoundingBox -1.0 -2.5 -5.0 1.0 2.5 5.0 !SetCamera !OpenDevice