Three.js uses *matrices* to encode 3D transformations---translations (position), rotations, and scaling. Every instance of [page:Object3D] has a [page:Object3D.matrix matrix] which stores that object's position, rotation, and scale. This page describes how to update an object's transformation.
There are two ways to update an object's transformation:
object.position.copy( start_position );
object.quaternion.copy( quaternion );
By default, the *matrixAutoUpdate* property is set true, and the matrix will be automatically recalculated.
If the object is static, or you wish to manually control when recalculation occurs, better performance can be obtained by setting the property false:
object.matrixAutoUpdate = false;
And after changing any properties, manually update the matrix:
object.updateMatrix();
object.matrix.setRotationFromQuaternion( quaternion );
object.matrix.setPosition( start_position );
object.matrixAutoUpdate = false;
Note that *matrixAutoUpdate* must be set to *false* in this case, and you should make sure not to call *updateMatrix*. Calling *updateMatrix* will clobber the manual changes made to the matrix, recalculating the matrix from *position*, *scale*, and so on.
An object's [page:Object3D.matrix matrix] stores the object's transformation relative to the object's [page:Object3D.parent parent]; to get the object's transformation in world coordinates, you must access the object's [page:Object3D.matrixWorld].
When either the parent or the child object's transformation changes, you can request that the child object's [page:Object3D.matrixWorld matrixWorld] be updated by calling [page:Object3D.updateMatrixWorld updateMatrixWorld]().
Three.js provides two ways of representing 3D rotations: [page:Euler Euler angles] and [page:Quaternion Quaternions], as well as methods for converting between the two. Euler angles are subject to a problem called "gimbal lock," where certain configurations can lose a degree of freedom (preventing the object from being rotated about one axis). For this reason, object rotations are always stored in the object's [page:Object3D.quaternion quaternion].
Previous versions of the library included a *useQuaternion* property which, when set to false, would cause the object's [page:Object3D.matrix matrix] to be calculated from an Euler angle. This practice is deprecated---instead, you should use the [page:Object3D.setRotationFromEuler setRotationFromEuler] method, which will update the quaternion.