I'm rigging an aircraft for use in Unity 3D and I need to place the object axis i.e. the "center" of each object so that it aligns with things like the edge or a point on the object such as aligning the center with a door edge to make it hinge properly. Is there an easy way to align the object axis with parts of an object, or for that matter the parts of another object? I'm using a plugin to move the axis to the object center, but also need to align it with other parts of the object.

Hit 'P' to bring up the snapping menu. Turn on 3D snapping and you can select a lot of different things to snap to. The object being snapped can't be a primitive though, because you can't move its axis independently of the object as you can with a polygon mesh. But you can easily snap the axis of a polygon object to another object's edge, points, etc. using this method.

 Thanks for the reply. I've tried the snapping to point which is easy enough. Can you make the rotation somehow snap too? So, if I drag the object axis center to a point it snaps, but can I then get one of the axis to snap to lets say an edge connected to the point?

I'm not entirely sure what you mean. You can snap to edges, yes. Turn that on and move the axis until it snaps to the desired edge. Then use the appropriate axis arms to move the axis along the edge until it's at the position you want. 

Is that any help?

 Thanks. It be nice if there was some snapping of the rotation too.  I can rotate the axis so they align with an edge by eye, but it takes some effort and might not be 100% reliable. For example, I might have a trapezoidal solid. I can snap the axis to a corner point of the solid, but then I want the x axis to be pointing exactly along a non-right angle side edge of the trapezoid. So rotating the y and z by eye works, but it be nice if it "snapped" when it got close. Its critical that the axis aligns with the edge to make the realtime animation playback accurate.

You want to 'Align to Edge' - I had a similar problem ages ago and never really got a reliable solution - not at work at the mo - will try to answer tonight, don't let that stop anyone else though!

James

In a bit of a rush here but check out Cactus Dan's plugin "CD Transfer Tools".

/Anders