Frequently Asked Questions

Q1: I create an alignment object using the local setter putting in a local rotation. When I print the alignment object I see that the global transformation is not a pure rotation. Isn't that wrong?
No, that's fine, even though it can be unintuitive. The reason is that when expressing transformations in a given reference system (RS), you can only rotate around the origin of that RS. This implies that when you have a tilt (local rotation), in global RS it corresponds in general to a rotation (around the origin of the global RS) plus a shift which moves back the origin of the local system to its original position.

Let us make a simple example, illustrated by the figure below. The axes for the global RS (x _G,y _G,z _G), drawn in blue, are such that the x _G axis is exiting the screen, y _G points to the right and z _G upwards. A module is placed at (0,100,0) and its local RS (x _L,y _L,z _L) is such that the y _L axis is coincident with y _G, the x _L and Z _L axes are parallel to x _G and z _G respectively. If we now apply a tilt (local rotation) by e.g. 10 degrees around x _L, this is seen in the global RS as a rotation by 10 degrees around x _G (1) plus a shift of 100*(0,1-cos(10),-sin(10)) to shift the center of the module back where it was (2).