In object graphics, it is very easy to rotate graphics atoms around the origin using the IDLgrModel::rotate method. But this rotation is always rotating around the origin. What if you want to rotate about a non-origin point? The technique is simple: translate the point of rotation to the origin, rotate, and translate back.

VISgrModel (docs) is a replacement for IDLgrModel that makes this a bit less of a hassle. It is created in the same way as IDLgrModel and used like this:

model->rotate, [0, 1, 0], 1, about=[-0.5, 0., 0.]

The default value for ABOUT is [0., 0., 0.], so it falls back to the standard IDLgrModel behavior.