The modeling block begins with a line !BeginModeling,
and ends with a line !EndModeling.
Three kinds of 3D data are described between them.
The available 3D primitives, attributes, and markers are listed later together with a detailed description of their formats.
The current body coordinates are defined by the following two lines:
/Origin Ox Oy Oz /BaseVector e1.x e1.y e1.z e2.x e2.y e2.z
where (Ox, Oy, Oz) is the origin of
the current body coordinates.
Orientation of the current body coordinates is defined with
a set of base vectors, i.e.,
x-directional base vector (e1.x, e1.y, e1.z)
and y-directional base vector (e2.x, e2.y, e2.z).
Z-directional base vector is defined as
(e1.x, e1.y, e1.z)
(e2.x, e2.y, e2.z).
The base vectors need not be normalized.
The origin and the base vectors are expressed in terms of the world
coordinates.
(There is no concept of hierarchical coordinate transformation.)
The default current body coordinates, which need not be
explicitly described are:
/Origin 0.0 0.0 0.0 /BaseVector 1.0 0.0 0.0 0.0 1.0 0.0
In other words, the default current body coordinates are identical with the world coordinates.
Attributes are able to be assigned to 3D primitives.
The most important one is color: /ColorRGB R G B.
For example, a red box is described by putting a line
/ColorRGB 1.0 0.0 0.0 before a line /Box ....
Each of R (red), G (green), and B (blue) components of color
should take a value between 0 and 1.
The default color which need not be explicitly
described is white, which is equivalent to /ColorRGB 1.0 1.0 1.0.
Once current body coordinates or current attributes are set,
they remain effective until
they are explicitly described later again with other values.
Example: Red box centered at position (1, 2, 3)
!BeginModeling /Origin 1 2 3 /ColorRGB 1 0 0 /Box 0.5 2.0 4.5 !EndModeling