Check if point is inside a custom mesh geometry - three.js

Question

What would be the easiest way to check if a point is inside a custom (irregular) mesh geometry?

Answer 1

If your mesh is close-up. You can use the THREE.js built-in ray-caster. Sample code is as
const point = new THREE.Vector3(2,2,2) // Your point
const geometry = new THREE.BoxBufferGeometry( 5, 5, 5 )
const material = new THREE.MeshBasicMaterial( { color: 0xffff00 } )
const mesh = new THREE.Mesh( geometry, material )
const raycaster = new THREE.Raycaster()
raycaster.set(point, new THREE.Vector3(1,1,1))
const intersects = raycaster.intersectObject(mesh)
if( intersects.length %2 === 1) { // Points is in objet
console.log(`Point is in object`)
}
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Answer 2

Just raycast once from the point to any direction, then check the intersects num, if is odd, the point is in the geometry, here is the demo

Answer 3

This is a computational geometry problem. You can look at Finding if point is inside geometry. Since your geometry is irregular the problem is much harder.
But if precision is not too important you can check if the point is inside the bounding box of the geometry.

Answer 4

Its better to check it using the dot product of ray direction and face normal
tested on three.js (r103)
const point = new THREE.Vector3(2, 2, 2) // Your point
const direction = new THREE.Vector3(1, 1, 1);
const geometry = new THREE.BoxGeometry(5, 5, 5)
const material = new THREE.MeshBasicMaterial({ color: 0xffff00, side: THREE.DoubleSide });
const mesh = new THREE.Mesh(geometry, material)
const raycaster = new THREE.Raycaster()
raycaster.set(point, direction)
const intersects = raycaster.intersectObject(mesh);
if (intersects.length && direction.dot(intersects[0].face.normal) > 0) {
console.log(`Point is in object`);
} else {
console.log(`Point is out of object`);
}
In rare cases you can get even number of interections with point located inside the mesh
(try point = new THREE.Vector3(0, 0, 0), that should give 4 intersections)