Detecting when GameObject arrives at target position using "transform.forward"

Unity Engine
1

Hi everyone!

I’m working on an AR app in which users are able to add 3D models of robots to the AR visualization, and can also make them move and rotate with the use of a GUI. In this GUI, users can make the robots rotate around their own Y axis by entering the rotation in degrees, and can make them move forward by entering the number of “distance units” they want the robot to move.

The rotation works fine, but I’m having a problem with the forward movement: the robot model (which is a gameObject) keeps going forward infinitely, no matter how many “distance units” it was programmed to move or which direction it is facing.

Basically, I’m using a “targetPosition” variable, the value of which is the result of the robot’s “transform.position” vector added to the “move forward” vector (which is basically (0, 0, moveUnits)). Then, I use a conditional loop to determine if the robot’s “transform.position” is equal to “targetPosition”. While this condition has not been met, the robot keeps moving forward by using “transform.forward”.

This is my current C# code for the forward movement (all the variables are global and were previosly declared in the code):

    public void PreMove(float moveUnits)
    {

        moveVector = Vector3.forward * moveUnits;

        targetPosition = transform.position + moveVector;

        //this state calls the Move() function below, which runs inside FixedUpdate():
        state = robotState.Move;

    }


    public void Move()
    {

        //checks if the robot's current position is equal to the target position:
        if (transform.position != targetPosition)
        {

            transform.position += transform.forward * Time.deltaTime * moveSpeed; //moves the robot forward

        }

        else
        {

            state = robotState.Idle; //changes the robot state to neutral

        }

   }
2

Don’t compare vectors (or any floating points) for equality. Unless you assign a float to another, it’s unlikely to be equal due to floating point precision issues.

Instead either check for distance (Vector.Distance()) or some other non-equality comparison.

If the robot is moving very fast, you may need to do additional steps, such as perhaps:

  • make the distance radius much larger

  • detect the transition from distance getting smaller to distance getting bigger (as it passes the objective)

  • upon detecting it, doing a force-set back to where you want it, IF precision matters.

1 Like
3

I would say that the objects position is never exactly equal to the target position. Put in some Debug.Log statements showing the objects position on every frame and see if it ever matches the target position.

And what Kurt Said!

1 Like
4

This is great advice, but be advised the default .ToString() that Unity uses only displays Vector3 objects to one decimal place. This means:

var a = new Vector3( 0.01f, 0, 0);
var b = new Vector3( 0, 0, 0.01f);

will both print out as:

(0.0, 0.0, 0.0)```

And the confusion will deepen when those two values do NOT test as equal.
1 Like
5

Hi everyone!
Thank you for the help! I was able to make it work correctly by using a float variable “distBetween” which received the value returned by “Vector3.Distance(targetPosition - transform.position)”, like you had suggested. Then, I changed the conditional loop to this:

if (distBetween > 0.1){

    transform.position += transform.forward * Time.deltaTime* moveSpeed

}

I also had to edit the “PreMove()” function slightly, to take the robot’s rotation into account when calculating the target position:

public void PreMove(float moveUnits)
    {
        moveVector = transform.forward * moveUnits;
        targetPosition = transform.position + moveVector;
        state = robotState.Move;
    }

Now everything is working as expected! Thanks again guys!

1 Like