Question of Parameter in geo struct

[PengJinHuang]

In geo struct, There is two parameter named geo.COR and geo.offOrigin, the geo.COR is displacement for centre of rotation correction, and geo.offOrigin is the Offset of image from origin, why we cant combine two parameter as one which discribe the displacement for centre of img to origin(assumed as rotation center) ?

[AnderBiguri]

@PengJinHuang They can indeed be made to be the same. However, geo.COR is a very standard parameter in machines where the sample rotates, that while could be fully described by a sin-wave geo.offOrigin, it just makes it much easier to get defined as is for convenience.

in essence, most people that know that have a COR shift will just need to set that parameters, while geo.offOrigin is a more general/abstract/vague parameters, mostly used in cases with non-standard geometries.

However note that geo.offIrigin moves the origin of the volume, but not the axis of rotations. Not that it invalidates your comment, but just to clarify that geo.COR = acos(geo.offOrigin(2)), they are related, but not the same