RaycastHit.distance

Description

Расстояние от начала луча до точки столкновения.

In the case of a ray, the distance represents the magnitude of the vector from the ray's origin to the impact point.

In the case of a swept volume or sphere cast, the distance represents the magnitude of the vector from the origin point to the translated point at which the volume contacts the other collider.

Note that RaycastHit.point represents the point in space where the collision occurs.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public float moveForce = 1.0F;
    public float rotateTorque = 1.0F;
    public float hoverHeight = 4.0F;
    public float hoverForce = 5.0F;
    public float hoverDamp = 0.5F;
    public Rigidbody rb;
    void Start() {
        rb = GetComponent<Rigidbody>();
        rb.drag = 0.5F;
        rb.angularDrag = 0.5F;
    }
    void FixedUpdate() {
        rb.AddForce(Input.GetAxis("Vertical") * moveForce * transform.forward);
        rb.AddTorque(Input.GetAxis("Horizontal") * rotateTorque * Vector3.up);
        RaycastHit hit;
        Ray downRay = new Ray(transform.position, -Vector3.up);
        if (Physics.Raycast(downRay, out hit)) {
            float hoverError = hoverHeight - hit.distance;
            if (hoverError > 0) {
                float upwardSpeed = rb.velocity.y;
                float lift = hoverError * hoverForce - upwardSpeed * hoverDamp;
                rb.AddForce(lift * Vector3.up);
            }
        }
    }
}

See Also: Physics.Raycast, Physics.Linecast, Physics.RaycastAll.