The rotation of modules is stored in the Db as eg:
-1 0 0 x y z rotx roty rotz
where: x, y, z, are the translations of the barrel modules, and rotx, roty, rotz are the Euler angles corresponding to the rotation of the modules.
However the question arises what is the origin around which these rotations take place?
The figure below shows the module 1,0,0. with the alignment 0 0 0 0 0 0 in the db. The black points are the straws in the module, the blue points are the points that the TRTAlignAlg uses to calculate the cog for this module and the red point in the cog used by the alignment algorithm
The figure below shows the same module with alignment 0 0 0 0.05 0 0.05 in the db. The black points are the straws in the new geometry, and the blue and red points are the cog from the previous geometry. Here we see that the rotation is NOT a rotation about the center of gravity of the modules, but more like a rotation about the origin of the global coordinate frame.
The figure below shows the same plot but with a rotation of pi/2. 0 0 0 0.785 0 0.785
