ピンチイン/ピンチアウトでモデルを拡大/縮小する処理

Pinch.cs

using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class Pinch : MonoBehaviour {

    public float pinchSpeed = 0.05f;    //ピンチ時移動速度

    private GameObject camera;          //メインカメラ
    private Vector2[] beforePoint;      //1フレーム前のポイント(各指)
    private Vector2[] nowPoint;         //現フレームのポイント(各指)

    void Start() {
        camera = this.transform.Find("MainCamera").gameObject;
        beforePoint = new Vector2[2];
        nowPoint = new Vector2[2];
    }

    void Update() {
        //2本目の指が押下された際
        if (Input.GetTouch(1).phase == TouchPhase.Began) {
            beforePoint[0] = Input.GetTouch(0).position;
            beforePoint[1] = Input.GetTouch(1).position;
        }
        //2本目の指が移動した場合
        if (Input.GetTouch(1).phase == TouchPhase.Moved) {
            nowPoint[0] = Input.GetTouch(0).position;
            nowPoint[1] = Input.GetTouch(1).position;


            //各指間の距離を取得し、前フレームとの差分の分、カメラを前後に移動させる
            float nowPointDistance = Vector2.Distance(nowPoint[0], nowPoint[1]);
            float beforePointDistance = Vector2.Distance(beforePoint[0], beforePoint[1]);
            float distance = nowPointDistance - beforePointDistance;
            distance *= pinchSpeed * Time.deltaTime;

            //現在の角度に応じて移動方向を算出
            Vector3 direction = Quaternion.Euler(0, camera.transform.localEulerAngles.y, 0) * new Vector3(0, 0, distance);
            direction = transform.TransformDirection(direction);
            camera.transform.position = new Vector3(camera.transform.position.x + direction.x, camera.transform.position.y + direction.y, camera.transform.position.z + direction.z);


            //現フレームのポイントを格納
            beforePoint[0] = nowPoint[0];
            beforePoint[1] = nowPoint[1];
        }
    }
}