Change here the type of group, 
Container or 
Polytope,
(or list of groups, previously selected with Group->Select, when 
Global is pressed). Parameters for empty entries or 
Local
choices remain unchanged.
Container
The primary purpose of a group container is to contain other objects.
When a group container is created, it has no child objects and consequently 
no visual representation. The only way to select an empty group is 
thus to write its identification or to use the mechanisms provided 
by 
Group->Select.
To avoid this problem, when 
Ok is pressed and the new group is 
created, the dialog 
Group->Create is automatically replaced by 
Group->Link, with the new group identification already inscribed 
on it. How to link objects to a group is described in the section 
Group Link.
Polytope
For an arbitrary cloud of atoms, defined by 
Central and
Neighbours settings, build a coordination polyhedron defined
by the smallest convex polygonal representation that surrounds all
the atoms. This is often used in Crystallography to build tetrahedra,
octahedra, and other small regular solids, but the method can be used
to build polyhedra for an arbitrary set of atoms, independently of
their position or number.
When Gamgi cannot build a 3D polyhedron, automatically tries to build 
a 2D atomic plane, as in 
Plane->Create. When a 2D plane cannot 
be defined, automatically tries to build a 1D atomic direction, as in
Direction->Create. When a 1D direction cannot be defined, an 
error is shown.
Central
Enter here the name and number of the central atom, around which the 
coordination polyhedron will be built. Pressing the mouse over an atom 
in the current layer, the atom identification is automatically written 
in the 
Central entry.
When 
Local is selected (the default), only one polyhedron is
constructed, around the 
Central atom. When 
Global is 
set, Gamgi builds coordination polyhedra around all the atoms in 
the sampling universe with the same element as the 
Central
atom.