Align Rotation

The cell orientation is given by two vectors, normal to each other,
defining an axes set. The reference orientation is given by two
vectors, normal to each other, defining an axes set.
### Cell

The first line defines a vector normal to the plane indicated
by entries **h**, **k**, **l**. The second line defines
a vector parallel to the direction indicated by entries **u**,
**v**, **w**. The two vectors must be normal to each other,
otherwise an error is shown. The two vectors are perpendicular
when the Weiss law is obeyed: hu + kv + lw = 0.
The **h**, **k**, **l** and **u**, **v**, **w**
cell coordinates can be given in terms of **Conventional**
or **Primitive** vectors, using the **Vectors** menu.
### Reference

The reference can be the current layer (the default) or another
cell. To select a cell as reference, press **Cell** and click
on its visual representation (or write its identification directly
on the enabled entry).
When the reference is a cell, the orientation is defined
by a plane and a direction, or vice-versa. When the reference
is the layer, two directions must be entered, based on the layer
orthonormed axes.

This alignment consists in rotating the cell, so the first cell vector is aligned with the first reference vector, and the second cell vector is aligned with the second reference vector.

The first line defines a vector normal to the plane indicated
by entries **h**, **k**, **l**, or parallel to the
direction indicated by entries **u**, **v**, **w**.
The second line defines a vector normal to the plane indicated
by entries **h**, **k**, **l**, or parallel to the
direction indicated by entries **u**, **v**, **w**.
The **h**, **k**, **l** and **u**, **v**, **w**
reference coordinates can be given in terms of **Conventional**
or **Primitive** vectors, using the **Vectors** menu.
When the reference is the layer, only the option **Conventional**
is available.

The two vectors must be normal to each other, otherwise an error is shown. When the reference is a cell, the Weiss law must be obeyed: hu + kv + lw = 0. When the reference is the layer, the layer axes are equivalent to the axes of a cubic primitive lattice, where planes are perpendicular to directions with the same indices, so one of the two directions can be seen as representing a plane with the same indices, thus the Weiss law must again be valid: u1u2 + v1v2 + w1w2 = 0.

Pressing **Ok** on the second level dialog, the **Align**
information is saved but the actual rotation is calculated only
after pressing **Ok** on the first level dialog, to ensure
that changing later some cell parameters will not produce
wrong results.

To disable the **Align** information, open again the
second level dialog, which now shows the previously
entered data, and press **Cancel**.