I have two characters that I turned into Digital Assets, each one has his own Animation Rig. One is a baby and the other is an adult that carries him. How can I parent the baby to the arm of the adult? To be more specific, how can I parent the main controller (placer) of the baby to the wrist controller of the Adult?

I rigged both character using Biped Auto Rig.

Any help would be great!

Take a look at the Sticky object, which can use the uv coordinates of your parent object and then the baby can be a child of the Sticky.

A simple Fetch object will do if you just want to parent between null objects. However, I think the real question is how to do this nicely within the autorigs. I think the easiest way is to modify the animation rig of the baby to do the parenting.

To augment Peter's and Ed's response, there are three methods to constrain one object to another outside parenting and blend objects. No parenting.

Rivet Object
This allows you to pick one, two, three or more points and it returns you a position in space. One point only returns the position. Two points returns you the average of two points plus rotation constraint in one direction. Supply three or more points and you get both position and orientation based on the plane that these three or more points form.

Sticky Object
This allows you to define your own uv co-ordinate system on the target geometry then returns a location using u and v position specified. It is quite common to create your own uv attribute, say uv_sticky or uv2 (if you want to use the Layer SOP) and not corrupt your existing texture uvs. You can have multiple sets of uvs and multiple sticky objects.
If you knew that you were only interested in sticking things to the arms of a critter, you could use cylinder uv mapping on each arm and define each as uv_leftarm and uv_rightarm using a combination of the Layer SOP and the Attribute SOP to rename the uv layers appropriately.

Fetch Object
This simply allows you to pull the full object Transformation and returns you the position and orientation in space free of any need to parent this object.

Which ones you choose is pretty simple. If you want to constrain to just an object in the rig, use Fetch.
If you want to bind your object to the actual deforming surface, use either Sticky or Rivet.

To choose between Sticky or Rivet is based whether you want to slide the constrained object on the target surface or not.
Sticky gives you the ability to slide freely over the target geometry as long as the uv attribute is nicely defined.
Rivet only allows you to slide on the current face (if you use 3 or more points that is).

Be careful if you are rendering with sub-d's as these last two tools do NOT work on the sub-d limit surface… Many times a quick Subdivide SOP after your deformer and only on that region of interest gets you close.


-jeff