I was designing a film reel that rotates. When I created the object I carefully used a grid, identified the centre point of the layer. Highlighted that with ruler lines. and created all my (fixed ratio) circles from this point. At no point have I moved off this centre reference. The centre lined up perfectly.
Yet, when it comes to doing a rotation about the centre, the centre point wobbles as it rotates. What is more odd is that after a while it completely loses it's centre and ends up having a non-centred rotation.
Is it not possible for Photoshop to retain it's exact centre point? Am I doing something that Photoshop is not really designed to do?
Is this an issue of me confusing the centre point of a layer box rather than the centre point of the shape that is within it? Is that is what is throwing it off?
I suspect that despite being careful, the center is still not perfectly aligned.
If you select the layer -- i.e. control-click on the layer in the layers palette so that the solid areas are selected -- and have snap turned on, you can drag a horizontal and vertical ruler which snap to the center of the selection. That will show you exactly where the center of rotation for that layer is.
Actually, control-T for transform should also show the center of rotation for the layer.
Also, even a single rogue pixel outside the area of the wheel will throw off the center of the layer, so you might want to draw a new circluar selection from the center point of the layer (centered on it) to the edge of the wheel, invert selection and delete. That would get rid of anything extra outside the wheel on that layer.