How to get vertices of obj model object in Three.JS? - three.js

Question

After loading a .obj model in Three.js I am unable to find vertices data. Vertices data is needed to apply collision detection as suggested by this answer
var loader = new THREE.OBJLoader();
loader.load('models/wall.obj', function ( object ) {
object.traverse( function ( node ) {
if ( node.isMesh ) {
console.log(node);
}
});
scene.add( object );
});
In mesh there is geometry.attributes.position.array but I am unable to find "vertices" anywhere in object.
Right now trying to convert position.array data to vertices but below code is not working, this answer is pointing the problem correctly but I am unable to use it to solve the issue:
var tempVertex = new THREE.Vector3();
// set tempVertex based on information from mesh.geometry.attributes.position
mesh.localToWorld(tempVertex);
// tempVertex is converted from local coordinates into world coordinates,
// which is its "after mesh transformation" position

Answer 1

geometry.attributes.position.array IS the vertices. Every three values makes up one vertex. You will also want to look at the index property (geometry.index), because that is a list of indices into the position array, defining the vertices that make up a shape. In the case of a Mesh defined as individual triangles, every three indices makes up one triangle. (Tri-strip data is slightly different, but the concept of referencing vertex values by the index is the same.)
You could alternately use the attribute convenience functions:
BufferAttribute.getX
BufferAttribute.getY
BufferAttribute.getZ
These functions take the index into account. So if you want the first vertex of the first triangle (index = 0):
let pos = geometry.attributes.position;
let vertex = new THREE.Vector3( pos.getX(0), pos.getY(0), pos.getZ(0) );
This is equivalent to:
let pos = geometry.attributes.position.array;
let idx = geometry.index.array;
let size = geometry.attributes.position.itemSize;
let vertex = new THREE.Vector3( pos[(idx[0] * size) + 0], pos[(idx[0] * size) + 1], pos[(idx[0] * size) + 2] );
Once you have your vertex, then you can use mesh.localToWorld to convert the point to world-space.