what are they??
A pole vector constraint causes the end of a pole vector to move to and follow the position of an object, or the average position of several objects.In character setup, the pole vectors of IK rotate plane handles for arm joint chains are often constrained to locators placed behind the character.
In general, you will want to constrain a pole vector so that the joint chain does not unexpectedly flip when you manipulate the IK rotate plane handle. Because flipping can occur when the handle vector approaches or intersects the pole vector, you should constrain the pole vector so that the handle vector is unlikely to cross it.
For more information about pole vectors and IK rotate plane handles, see Chapter 20, “Using IK Rotate Plane Handles.”
