Check if point is inside a custom mesh geometry

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