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.

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.

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.

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.