问题

There are three ways about Detecting Intersections in RealityKit framework, but I don't know how to use it in my project.

func raycast(origin: SIMD3<Float>, 
          direction: SIMD3<Float>, 
             length: Float, 
              query: CollisionCastQueryType, 
               mask: CollisionGroup, 
         relativeTo: Entity?) -> [CollisionCastHit]

func raycast(from: SIMD3<Float>, 
               to: SIMD3<Float>, 
            query: CollisionCastQueryType, 
             mask: CollisionGroup, 
       relativeTo: Entity?) -> [CollisionCastHit]

func convexCast(convexShape: ShapeResource, 
               fromPosition: SIMD3<Float>, 
            fromOrientation: simd_quatf, 
                 toPosition: SIMD3<Float>, 
              toOrientation: simd_quatf, 
                      query: CollisionCastQueryType, 
                       mask: CollisionGroup, 
                 relativeTo: Entity?) -> [CollisionCastHit]

回答1:

Simple Ray-Casting

If you want to find out how to position a model made in Reality Composer into a RealityKit scene (that has a detected horizontal plane) using Ray-Casting method, use the following code:

import RealityKit
import ARKit

class ViewController: UIViewController {

    @IBOutlet var arView: ARView!
    let scene = try! Experience.loadScene()

    @IBAction func onTap(_ sender: UITapGestureRecognizer) {

        scene.steelBox!.name = "Parcel"

        let tapLocation: CGPoint = sender.location(in: arView)
        let estimatedPlane: ARRaycastQuery.Target = .estimatedPlane
        let alignment: ARRaycastQuery.TargetAlignment = .horizontal

        let result: [ARRaycastResult] = arView.raycast(from: tapLocation,
                                                   allowing: estimatedPlane,
                                                  alignment: alignment)

        guard let rayCast: ARRaycastResult = result.first
        else { return }

        let anchor = AnchorEntity(world: rayCast.worldTransform)
        anchor.addChild(scene)
        arView.scene.anchors.append(anchor)

        print(rayCast)
    }
}

Pay attention to a class ARRaycastQuery. This class comes from ARKit, not from RealityKit.

Convex-Ray-Casting

A Convex-Ray-Casting methods like raycast(from:to:query:mask:relativeTo:) is the op of swiping a convex shapes along a straight line and stopping at the very first intersection with any of the collision shape in the scene. Scene raycast() method performs a hit-tests against all entities with collision shapes in the scene. Entities without a collision shape are ignored.

You can use the following code to perform a convex-ray-cast from start position to end:

import RealityKit

let startPosition: SIMD3<Float> = [0, 0, 0]
let endPosition: SIMD3<Float> = [5, 5, 5]
let query: CollisionCastQueryType = .nearest
let mask: CollisionGroup = .default

let raycasts: [CollisionCastHit] = arView.scene.raycast(from: startPosition, 
                                                          to: endPosition, 
                                                       query: query,  
                                                        mask: mask, 
                                                  relativeTo: nil)

guard let rayCast: CollisionCastHit = raycasts.first
else { return }

rayCast.distance    /* The distance from the ray origin to the hit */
rayCast.entity      /* The entity that was hit                     */
rayCast.normal      /* The normal of the hit                       */
rayCast.position    /* The position of the hit                     */

A CollisionCastHit structure is a hit result of a collision cast and it lives in RealityKit's scene.

来源：https://stackoverflow.com/questions/60294367/how-to-use-raycast-methods-in-realitykit

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