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When rigging, there are many times when you'll need to control the rotation or orientation of a joint or another object. For that we can use the Orient constraint. So let's take a look at this very simple joint chain here. We have a three joint chain and let's go ahead and constrain the middle joint of that chain. I'm going to create a constraining object, so that's going to be a NURBS circle, so I'm going to go ahead and select NURB circle, draw a very simple circle, and then just move that into place.
In fact, let's go ahead and snap this to that joint to make it precise. So I'm going to turn on Snap here, move that, so that it snaps to that joint and then turn off Snap again. In order to set up the constraint, it's a very familiar process by now, all we have to do is select the constraining object or objects, and then Shift+Select the constrained object last. And let's go, Constrain > Orient constraint, let's go ahead and take a look at our options here. Before an Orient constraint, we do want to make sure we turn on Maintain Offset, that's probably the easiest way to use that.
Particularly with joints, because joints always have to have the X axis pointing along the axis of the joint, and that can create some issues when you go to constrain them. So I'm going to go ahead and click on Maintain Offset, and hit Add. Now when you do that we get the constraint. Now I'm going to go ahead and click off of this and then just select the NURB circle, and as you can see when I rotate that circle, I can rotate the joint.
Now you have to be careful not to double select, so if I select the joint and the circle, and I rotate, you're going to get all sorts of havoc here. And that's because we're double-rotating, we're rotating the circle and the joint. We can eliminate the possibility of that problem by selecting the joint itself, going into the Attribute Editor, under Orient Constraint, and then go down to Lock Output, and make sure we have that turned on, so that way the joint can't rotate separately from the circle, and now the circle completely controls the rotation of this joint.
Now if you don't want to use offset, you can get it to work. Let me show you how this would work. I'm going to go ahead and select my circle, and let's go ahead and delete that circle. And we're going to go ahead and redo this. So let's go ahead and create another NURBS curve here, and position it in place. Now the problem with this is that, as you can see, the NURBS curve, it depends on how you create it as to where the X axis is pointing.
So in this case the X axis is pointing left and right, and in this joint the X axis is pointing straight down, so if I constrained orientation and turned off Maintain Offset, the joint is going to snap to the X axis of that circle. And that's not really what we want, so what we have to do is we're not going to use Offset, we have to make sure that the X axis of whatever it is your constraining, is pointed along at an appropriate direction.
So let's go ahead and delete this, and in this case I'm going to go ahead and create this circle in the side view. I'm going to go ahead and select my NURBS circle, make sure I have Snap turned off here, and then just go ahead and draw that. Now when what I draw it in a side view, the X axis is actually positioned properly along that circle. So all I have to do is rotate that circle into place. So let's go ahead and rotate it 90 degrees or actually in this case -90 degrees, and then just move that in to place, in fact, we can snap that to that joint.
So now I have a circle with the X axis pointing down, and I also have a joint with the X axis pointing down, so if I select my circle, Shift+Select my joint, do Constrain > Orient constraint, make sure Offset is off, now this is going to be aligned with that circle. I can just select the circle itself and we have that working without an offset. Orient constraints allow you to control the rotation of objects, and this can be used a lot in character animation and rigging.
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