# Group Modify

- Type
- Scope
- Tolerance
- View

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.
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