Develop Reference

Get object position in a three.js scene dynamically

I am new to threejs.
I have scene with an object in it which we can move around the scene on all the XYZ Axis using TransformControls.js.
When I translate/move the object inside the scene using mouse click and drag on any of the axis (i.e X,Y,Z). I want to get the updated X,Y,Z position co-ordinates of that particular object inside the scene.
I use mesh.position.set( 0, 0, 0 ); to set position of the object prior rendering the scene, But I am not able to find how to get the dynamic position of an object inside a scene.
Eventually I want to save the updated position co-ordinates after the transform operation and re-render the scene with the object at the updated position co-ordinates when the user comes back to the page or does a page refresh.
Any pointers would be very helpful.
Thank you

THREE.TransformControls requires a few steps to use.
Create your THREE.TransformControls object
Add it to your scene
Attach it to the object you wish to manipulate
var xformControl = new THREE.TransformControls(camera, renderer.domElement);
scene.add(xformControls);
// assuming you add "myObj" to your scene...
xformControl.attach(myObj);
// and then later...
xformControl.detatch();
Attaching the control to an object will insert a manipulation "gizmo" into the scene. Dragging the various parts of the gizmo will perform different kinds of transformations. After you are done transforming the part with the gizmo, checking mesh.position should reflect the new position.
Additional information for clarity:
The position of the object will not be updated until you use the "gizmo" to move it. Example:
Your object is in the scene at (10, 10, 10)
xformControl.attach(yourObject)
The "gizmo" is created at (10, 10, 10)
Your object remains at (10, 10, 10)
Use the "gizmo" to translate the object in +Y direction
Your object will now have an updated position
console.log(yourObject.position.y > 10); // true

I might be too late, but you can get the updated value by using TransformControls' objectChange event.
Example code:
const transformControls = new TransformControls(camera, renderer.domElement);
transformControls.addEventListener('objectChange', (e) => {
console.log(e.target.object.position.x);
})

first answer is not correct, it should be:
onst transformControls = new TransformControls(camera, renderer.domElement);
transformControls.addEventListener('objectChange', (e) => {
console.log(e.target.object.position.x);
})

XTK - Toolkit.. the cube moves by should only rotating

Im a newbie in 3D computer graphics and seen an odd thing.
I used the XTK-Toolkit, witch is great with DICOM. I add a cube in the scene and translated it far from the center (http://jsfiddle.net/64L47wtd/2/).
when the cube rotate it looks like it is moving
Is this a bug in XTK, or an principle problem with 3D rendering?
window.onload = function() {
// create and initialize a 3D renderer
var r = new X.renderer3D();
r.init();
// create a cube
cube = new X.cube();
// skin it..
cube.texture.file = 'http://x.babymri.org/?xtk.png';
cube.transform.translateX(250);
cube.transform.translateY(200);
cube.transform.translateX(270);
r.add(cube); // add the cube to the renderer
r.render(); // ..and render it
// add some animation
r.onRender = function() {
// rotation by 1 degree in X and Y directions
cube.transform.rotateX(1);
cube.transform.rotateY(1);
};
};

You miss to consider the cube a compound object consisting of several vertices, edges and/or faces. As a compound object it's using local coordinate system consisting of axes X, Y, Z. The actual cube is described internally using coordinates for vertices related to that cube-local coordinate system.
By "translating" you declare those relative coordinates of vertices being adjusted prior to applying inside that local coordinate system. Rotation is then still working on the axes of that local coordinate system.
Thus, this isn't an error of X toolkit.
You might need to put the cube into another (probably fully transparent) container object to translate/move it, but keep rotating the cube itself.
I tried to extend your fiddle accordingly but didn't succeed at all. Taking obvious intentions of X Toolkit into account this might be an intended limitation of that toolkit for it doesn't obviously support programmatic construction of complex scenes consisting of multi-level object hierarchies by relying on its API only.

How to Change a Box's dimensions/size after creation?

One can easily create a THREE.BoxGeometry where you have to pass arguments when creating as three separated arguments for width, height, and depth.
I would like to create any and all THREE[types]() with no parameters and set the values after that.
Is there a way to set the dimensions/size of the box geometry after creation (possibly buried in a Mesh already too)? other then scaling etc.
I couldn't find this in the documentation if so, otherwise maybe a major feature request if not a bug there. Any thoughts on how to classify this? maybe just a documentation change.

If you want to scale a mesh, you have two choices: scale the mesh
mesh.scale.set( x, y, z );
or scale the mesh's geometry
mesh.geometry.scale( x, y, z );
The first method modifies the mesh's matrix transform.
The second method modifies the vertices of the geometry.
Look at the source code so you understand what each scale method is doing.
three.js r.73

When you instantiate a BoxGeometry object, or any other geometry for that matter, the vertices and such buffers are created on the spot using the parameters provided. As such, it is not possible to simply change a property of the geometry and have the vertices update; the entire object must be re-instantiated.
You will need to create your geometries as you have the parameters for them available. You can however create meshes without geometries, add them to a scene, and update the mesh's geometry property once you have enough information to instantiate the object. If not that, you could also set a default value at first and then scale to reach your target.

Technically, scaling only creates the illusion of an updated geometry and the question did say (other then scaling). So, I would say a better approach would be to reassign the geometry property of your mesh to a new geometry.
mesh.geometry = new THREE.BoxGeometry(newSize, newSize, newSize)
With this approach you can update any aspect of the geometry including width segments for example. This is especially useful when working with non box geometries like cylinders or spheres.
Here is a full working example using this approach:
let size = 10
let newSize = 20
// Create a blank geometry and make a mesh from it.
let geometry = new THREE.BoxGeometry()
let material = new THREE.MeshNormalMaterial()
let mesh = new THREE.Mesh(geometry, material)
// Adding this mesh to the scene won't display anything because ...
// the geometry has no parameters yet.
scene.add(mesh)
// Unless you intend to reuse your old geometry dispose of it...
// this will significantly reduce memory footprint.
mesh.geometry.dispose()
// Update the mesh geometry to a new geometry with whatever parameters you desire.
// You will now see these changes reflected in the scene.
mesh.geometry = new THREE.BoxGeometry(size, size, size)
// You can update the geometry as many times as you like.
// This can be done before or after adding the mesh to the scene.
mesh.geometry = new THREE.BoxGeometry(newSize, newSize, newSize)

three js same position (reference) for 2 Object3D()

I am trying to add 2 (or more) Meshes to the same scene, but i want all the Object3D to share the same position (but with a different rotation for each object).
I know the ".copy()" method, but in my case, there are so many objects and using a loop to change the position of all the objects (60 times per seconds) is resulting a poor performance.
So, I tried to use the same position reference for the objects:
var o=new THREE.Object3D(); // the first object
var p=new THREE.Object3D(); // the second object
o.position=p.position; // the position of the first object becomes the reference to the position of the second object
o.position==p.position; // false, but why?
But it isn't working and I don't get why!
My question is:
Is it possible to change the position reference of a THREE.Object3D()?
And if it isn't, how can I improve the performance of my scene?
Thanks in advance!
Edit: seems to works for someone (this answer is exactly what i can't do): How to set the Object3D position and rotation same as the added mesh ? [three.js]

Three.JS: Get position of rotated object

In Three.JS, I am capable of rotating an object about its origin. If I were to do this with a line, for instance, the line rotates, but the positions of its vertices are not updated with their new locations. Is there some way to apply the rotation matrix to the position of the vertices to find the new position of the point? Say I rotate a line with points at (0,0,0) and (0,100,100) by 45° on the x, 20° on the y, and 100° on the z. How would I go about finding the actual position of the vertices with respect to the entire scene.
Thanks

yes, 'entire scene' means world position.
THREE.Vector3() has a applyMatrix4() method,
you can do the same things that the shader does so in order to project a vertex into world space you would do this
yourPoint.applyMatrix4(yourObject.matrixWorld);
to project that into camera space you can apply this next
yourPoint.applyMatrix4(camera.matrixWorld);
to get an actual screen position in -1 to 1
yourPoint.applyMatrix4(camera.projectionMatrix);
you would access your point like this
var yourPoint = yourObject.geometry.vertices[0]; //first vertex
also, rather than doing this three times, you can just combine the matrices. Didnt test this, but something along the lines of this. Might go the other way:
var neededPVMmatrix = new THREE.Matrix4().multiplyMatrices(yourObject.matrixWorld, camera.matrixWorld);
neededPVMmatrix.multiplyMatrices(neededPVMmatrix, camera.projectionMatrix);
if you need a good tutorial on what this does under the hood i recommend this
Alteredq posted everything there is to know about three.js matrices here
edit
One thing to note though, if you want just the rotation, not the translation, you need to use the upper 3x3 portion which is the rotation matrix, of the models world matrix. This might be slightly more complicated. I forgot what three.js gives you, but i think the normalMatrix would do the trick, or perhaps you can convert your THREE.Vector3() to THREE.Vector4(), and set .w to 0, this will prevent any translation from being applied.
edit2
if you want to move the line point in your example, instead of applying it to the particle, apply it to
var yourVertexWorldPosition = new THREE.Vector3().clone(geo.vertices[1]); //this is your second line point, to whatever you set it in your init function
yourVertexWorldPosition.applyMatrix4();//this transforms the new vector into world space based on the matrix you provide (line.matrixWorld)