In praise of the Geometry constraint, pt 2: a better point constraint?

The Geometry constraint is designed to constrain the position of object A to the surface of object B. Now what happens if you converge all of B's vertices to the same point in 3d space?

You get a point constraint.

So what ? There's already a Point constraint in the Maya toolset..

Sure there is, but I'm out to show you that this point constraint has some neat advantages over its namesake.

1) Create a Geometry constraint:

Create two polygon cubes.

Rename them A and B.

Select B, then A and add a Geometry Constraint (Animation > Constrain > Geometry), so as to constrain A to B.

Now A is constrained to the surface of B.

Remember from part 1, the Geometry constraint doesn't connect directly to any keyable attributes.

2) Turn it into a point constraint:

Select all the vertices of object B.

Move them all to the Origin.

You now have a point constraint that hasn't tied up your translation attributes.

3) Animating the constraint:

Of course you can still animate B, it's just an object after all.

But you can also animate the effect that the constraint has on A....although this is slightly different to how you may be used to adjusting the weight of a constraint.

  Turn the Geometry constraint off by setting
  its nodeState attribute to HasNoEffect.

  Turn the Geometry constraint on by setting
  the nodeState attribute to Normal.

 
The weight attribute has no effect, so no blending is possible.

4) Add a switch to control the effect of the constraint:

It's easier if the on/off switch for the constraint is on A's Transform node; then you don't have to find the geometryConstraint node to turn it on or off....plus all your keyable attributes are on the same node.

Select A.

Add an enumerated type attribute, called constraint, with values "on" and "off".

Use the Connection Editor to connect this attribute to the geometryConstraint attribute: nodeState:


 


connectAttr -f A.constraint A_geometryConstraint1.nodeState;

Note: I use an enum. attribute here because you can add values in the order you need them. You can use a boolean type attribute if you like, but you'll have to connect it to the nodeState attribute by Set Driven Key, or through a Reverse node.

There, a new kind of point constraint. Not convinced ?
You will be when I show you:

• how to set up a dual-point constraint
• an easy setup for an FK/IK rig.

Cheers,

Owen