unity3d 点击地形某一点,第一人称定位过去？

她。 3D打印店铺

public GameObject cameraObj;
void OnMouseDown()
{
    Vector3 objVector3 = Camera.mainCamera.WorldToScreenPoint(this.cameraObj.transform.position);
    Vector3 off = new Vector3(Input.mousePosition.x - objVector3.x, Input.mousePosition.y - objVector3.y, objVector3.z);
    Vector3 mousePositon = new Vector3(off.x +off.x+ Input.mousePosition.x,off.y +off.y+ Input.mousePosition.y, off.z);
    Vector3 posit = Camera.mainCamera.ScreenToWorldPoint(mousePositon);
    cameraObj.transform.position = new Vector3(posit.x,0.7499999f,posit.z);
}
把脚本赋给地形， 点击移动有问题。 谁有好的方法，告诉我一下