Scripting Reference
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Transform.TransformDirection

function TransformDirection (direction : Vector3) : Vector3

Description

Transforms direction from local space to world space.

This operation is not affected by scale or position of the transform. The returned vector has the same length as direction.

JavaScript 
    // Calculate the x-axis relative to the camera
    var cam : Transform = Camera.main.transform;
    var cameraRelativeRight : Vector3 = cam.TransformDirection (Vector3.right);
    // Apply a force relative to the camera's x-axis
    rigidbody.AddForce (cameraRelativeRight * 10);
using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public Transform cam = Camera.main.transform;
    public Vector3 cameraRelativeRight = cam.TransformDirection(Vector3.right);
    void Example() {
        rigidbody.AddForce(cameraRelativeRight * 10);
    }
}
import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public cam as Transform = Camera.main.transform

    public cameraRelativeRight as Vector3 = cam.TransformDirection(Vector3.right)

    def Example():
        rigidbody.AddForce((cameraRelativeRight * 10))

function TransformDirection (x : float, y : float, z : float) : Vector3

Description

Transforms direction x, y, z from local space to world space.

This operation is not affected by scale or position of the transform. The returned vector has the same length as direction.

JavaScript 
    // Calculate the x-axis relative to the camera
    var cam : Transform = Camera.main.transform;
    var cameraRelativeRight : Vector3 = cam.TransformDirection (1, 0, 0);
    // Apply a force relative to the camera's x-axis
    rigidbody.AddForce (cameraRelativeRight * 10);
using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public Transform cam = Camera.main.transform;
    public Vector3 cameraRelativeRight = cam.TransformDirection(1, 0, 0);
    void Example() {
        rigidbody.AddForce(cameraRelativeRight * 10);
    }
}
import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public cam as Transform = Camera.main.transform

    public cameraRelativeRight as Vector3 = cam.TransformDirection(1, 0, 0)

    def Example():
        rigidbody.AddForce((cameraRelativeRight * 10))