How to get the absolute position of a vertex in three.js?

Question

As far as I know var point = object.geometry.vertices[i]; will return with the relative position for the x, y and z of the point inside the geometry of the object.

How to get the absolute position, if the object was moved, rotated or scaled?

Answer 1

First make sure the object's matrices have been updated.

object.updateMatrixWorld();

The render loop usually calls this for you.

Then, do this:

var vector = object.geometry.vertices[i].clone();

vector.applyMatrix4( object.matrixWorld );

The vector will now contain the position in world coordinates.

You might want to read some CG reference books.

1. 3D math primer for graphics and game development / by Fletcher Dunn and Ian Parberry

2. Essential Mathematics for Games and Interactive Applications: A Programmer’s Guide James M. Van Verth and Lars M. Bishop

three.js r69

Answer 2

Recent versions of Three.js (v50+) provide this functionality built into the THREE.Object3D class. In particular, to get the world coordinates of a local THREE.Vector3 instance named vector, use the localToWorld method:

object.localToWorld( vector );

Similarly, there is a worldToLocal method for converting world coordinates into local coordinates, which is slightly more complicated, mathematically speaking. To translate a world vector into the objects local coordinate space:

object.worldToLocal( vector );