# Up Vector Constraints

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Aim constraints constrain an object’s orientation to aim at other objects. Aim constraints can and often used to aim a light or camera at an object or group of objects, or to set up a locator that controls eyeball movement. There are three vectors that constrain an object’s orientation if it uses the aim constraint: the Aim Vector, the Up Vector, and the World-Up Vector. These vectors cannot be seen in the workspace, but they will still effect the constrained object’s orientation, understanding these vectors can be a big help into understanding how a constrained object can unexpectedly roll. These three constraints rotate the constrained object so that the Aim Vector points in the direction specified, rotating the object about the Aim Vector…show more content…
Due to the Aim Vector not controlling how the object might rotate about, the Aim Vector itself does not completely constrain the object. The orientation of the object, however, is controlled by the Up Vector and the World-Up Vector. The Up Vector is the control of the orientations of the constrained object about the Aim Vector. The Up Vector is relative to the constrained object’s location. By default, the Up Vector tries to point in the same direction as the World-Up Vector, which is relative to the scene’s entire world space. The Up Vector positions the constrained object around the aim vector, and will attempt to align itself as closely as possible with the World-Up Vector. Despite how the object is rotated, if the Aim Vector and the Up Vector point in the same direction, the Up Vector will not move close to the World-Up Vector – stopping as soon as the Aim Vector aims at the object, disables the orientation from rotating, thus restricting the object from flipping. When you move the target, the constrained object’s Aim Vector moves to point at the target, orients the constrained object according to both objects, then the constrained object orients itself about the Aim Vector using the Up