Inverse of camera.lookAt()

I googled far and wide but I haven't found the solution to what I think to actually be a pretty common situation. Say I have a THREE.PerspectiveCamera initialized to look at a certain point in space:

var camera = new THREE.PerspectiveCamera(45, 2, 0.1, 100);
var target = new THREE.Vector3(1, 2, 3);
camera.lookAt(target);

Now, later on in the code I'd like to be able to find out the coordinates of target by simply querying camera.
I tried what suggested in this question, adapting it to my own scenario:

var vector = new THREE.Vector3();
vector.applyQuaternion(camera.quaternion);
console.log(vector);

But it logs a vector of coordinates (0, 0, 0) instead of the correct coordinates (which, in my example, should be (1, 2, 3)).
Any insights? Cheers.

EDIT:
Ok so I'm going to try to contextualize here, so as to justify why MrTrustworthy's solution is unfortunately not applicable in my scenario. I'm trying to tweak the THREE.OrbitControls library for my purposes, since I noticed that when using it, it overrides whichever position the camera was looking at originally. This has also been reported here. Basically, on line 36 of OrbitControls.js (I'm using the version which can be found here) this.target is initialized to a new THREE.Vector3(); I found out that if I manually set it to equal the same vector I use as argument of camera.lookAt() everything works just fine: I can start panning, orbiting and zooming the scene from the same POV I would see the scene from if I didn't apply the controls. Of course, I cannot hard-code this information into OrbitControls.js because it would require me to change it every time I want to change the initial "lookAt" of my camera; and if I were to follow MrTrustworthy's suggestion I would have to change line 36 of OrbitControls.js to read like this: this.target = object.targetRef (or this.target = object.targetRef || new THREE.Vecotr3()), which is also too "opinionated" (it would always require object to have a targetRef property, whereas I'm trying to stick to using only three.js's existing object properties and methods). Hope this helps get a better understanding of my case. Cheers.

回答1:

If your only usecase is "I want to be able to access the camera-targets position via the camera object", you could just put a reference into the camera object.

var camera = new THREE.PerspectiveCamera(45, 2, 0.1, 100);
var target = new THREE.Vector3(1, 2, 3);
camera.lookAt(target);
camera.targetRef = target;

//access it
var iNeedThisNow = camera.targetRef;

回答2:

I figured it out and wrote my solution here. Since the issue affects both THREE.TrackballControls and THREE.OrbitControls, the solution involves applying a slight change to both those files. I wonder if it can be considered a valid change and make its way to rev. 70; I will issue a PR on github just for the sake of it :)
Thanks to all those who pitched in.

回答3:

well you could put the object in parent, have parent lookat, and have the child object rotated 180 degrees. That's the quick noob solution