Local to World

local_to_world.js

    var parent  = new THREE.Object3d();
    var child   = new THREE.Object3d();
    parent.add(child);
    parent.position.y = 100;
    child.position.y  = 200;

    // we get 200, because child.position returns us the local position
    console.log( child.position.y );

    // we get 300, because child.localToWorld(new THREE.Vector3()) returns us the global position
    // the parameter for the localToWorld function is a THREE.Vector3() equal to THREE.Vector3(0,0,0)
    console.log( child.localToWorld( new THREE.Vector3() ).y );

    // we get 400, the Vector will be add on the returned Vector.
    // Notice: this dosen´t change the position values.
    console.log( child.localToWorld( new THREE.Vector3(0,100,0) ).y );

    // we get 300,it´s importend to clone, otherwise you get a Vector with zeros,
    // the reason is, that the vector will overriden without clone.
    var childPos = child.matrixWorld.getPosition().clone();
    console.log( childPos.y );