Orientation vs. Rotation

JoeMamma2000

A long while back someone was asking about the difference between orientation and rotation. I use both a lot, and I don't think anyone has really discussed it very much here, and at least IMO it's very important to really understand them. So I thought I'd give a brief description. Yeah, it's very simple and basic, but maybe it will help someone.

If you select an object in the scene and go into the Motion tab you'll see three sections: the first is for translation/moving the object in the XYZ plane, the second is for rotation of the object, and the third is for scaling/sizing the object. And in the rotation section you'll see two lines labelled "Orientation" and "Rotation".

First we need to discuss two aspects of 3D objects: the Center, and the Hot Point. The Center is a location calculated by the software, and is the average of all the points in the object. The center of a 12 inch long ruler is, obviously, at the 6 inch mark. For more complicated objects the same method applies. You average all the points' locations in XYZ space, and voila, there's the objects' center.

The Hot Point is an absolutely arbitrary point that YOU define, and determines the point that YOU want to describe as the center of all translation, rotation, and scaling. And YOU can adjust not only the location of that hotpoint in the XYZ space, but also adjust the rotation axes of the hotpoint. Basically you're setting up the center and orientation of the manipulator so that you can move, rotate, and scale your object the way you want to.

The hotpoint can be at the calculated Center of the object, but it doesn't have to be. It is where ever you want it to be. And you can also define the rotation axes around which your object will rotate. That is what hotpoint orientation is all about.

For example, lets say you load a simple automobile tire and a V4 into your scene, and they look like the attached image. This can, and probably has happened to you, for a number of reasons.

Bummer, right? Because if you rotate the V4 abdomen bone, for example, or rotate the tire like it's rolling down the road, what do you get? It's all cattywumpus. The tire wobbles, and V4 tilts sideways.

So how do you fix it? Well, you adjust the hotpoint orientation for the tire and the V4 abdomen. And the way you do this is to simply enter a value in the X, Y, or Z orientation fields, depending on which you want to modify. This re-orients the rotation axes of the manipulator. In this case, since the V4 abdomen orientation is off by about -30 degrees, you rotate the manipulator by about +30 degrees on the Z axis, and it will now be aligned with the correct axis so you can make her bend correctly at the waist. And the tire manipulator orientation is off by about +40 degrees, so you adjust the Z axis value by -40 degrees and the tire will roll down the road correctly.

Yeah, it might take a little trial and error to figure out how much to adjust the orientation to make it exactly where you want it, but it's fairly quick and painless.

Hope this helps.

DUDU

That's also usefull with the use of a Bend and Twist modifier, for exemple.
Thank you to share this !