Define here the type representation of the cell.
Type
Lattices can be represented using 
Conventional, 
Primitive 
or 
Wigner-Seitz cells, plus filtering volumes such as a 
Parallelepiped or a 
Sphere. Lattices can also be represented 
by the stereographic 
Projection of its crystallographic planes 
and directions (added by users, after the projection is created).
Cells with a 
Hexagonal system and a rhombohedral 
R lattice
(corresponding to the seven R space groups when using the standard Hermann-Mauguin
symbols), are always represented using the hexagonal axes and the obverse setting,
when the chosen type is 
Conventional, and the rombohedral axes, when the
chosen type is 
Primitive. Cells with a 
Hexagonal system and a
primitive 
P lattice (corresponding to all the other space groups from 143
to 194 that are not R) are always represented using full hexagonal prismas, when
the chosen type is 
Conventional, and one-third of the hexagonal prismas,
when the chosen type is 
Primitive.
n1, n2, n3
Set the number of cells to replicate, in the three directions of space, 
when the chosen type is 
Conventional, 
Primitive 
or 
Wigner-Seitz. When not needed, these parameters are disabled.
v1, v2, v3, v12, v13, v23
A 
Parallelepiped filtering volume is defined by three edge 
lengths, 
v1, 
v2, 
v3, plus the three angles between 
them, 
v12, 
v13, 
v23. Each angle must be smaller 
than the sum of the other two and must be larger than the absolute 
difference of the other two, otherwise an error is produced.
A 
Sphere filtering volume is defined by the radius 
v1.
When not needed, these parameters are disabled.
All nodes inside the volume representation are allocated (even if the
user choosed to hide them). In 
Parallelepiped and 
Sphere 
volumes, a small tolerance (by default 1.0E-4) is added around the volume 
space to make sure that nodes in the borders are included. For example, 
a sphere with 
v1 = 
1.0, filtering a cubic primitive lattice 
with 
a = 
1.0, allocates 1 + 2 + 2 + 2 = 7 nodes (without 
the tolerance, the result could be undefined).