Joints and constraints in rigging directly determine a 3D model’s movement behavior and structural stability during animation.
Joints act as pivot points, enabling core motions like rotation (e.g., elbows) or bending (e.g., knees), forming the model’s "skeleton" to define basic movement ranges.
Constraints, such as IK (Inverse Kinematics), limit, or parent-child constraints, restrict or guide movement—IK keeps limbs aligned when reaching, limit constraints prevent over-rotation, and parent-child links ensure hierarchical motion (e.g., a hand moving with an arm).
Together, they ensure the model moves in a controlled, realistic way, avoiding disjointed or unnatural poses and maintaining structural integrity.