Converting between local and global direction

Question

I'm using a forward direction vector of a gameobject like this: myGameobject.forward;

This vector however is a local direction. How can I convert direction into a global direction? And when I have a global direction, how can I convert it back to the local direction of a particular game object?

Answer 1

Best Answer

Answer by Bunny83 · Mar 06, 2013 at 12:20 PM

First a gameobject doesn't have a forward variable, only the Transform component of a GameObject. This forward vector is always in world space. The forward direction in local space is a constant value:

 Vector3.forward == Vector3(0,0,1)  // forward in localspace
 
 myGameobject.transform.forward     // forward in worldspace

To convert between local and world space you can use:

TransformDirection to transform a direction from local to world space
InverseTransformDirection to transform a direction from world to local space
TransformPoint to transform a position from local to world space
InverseTransformPoint to transform a position from world to local space.

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gtucker3d · Sep 19, 2021 at 07:29 AM 0

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Thanks mate this was awesome information but I think you have it backwards.

Vector3.forward == Vector3(0,0,1) // forward in Worldspace

myGameobject.transform.forward // forward in Localspace

Bunny83 gtucker3d · Sep 19, 2021 at 02:26 PM 0

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No, it's not backwards, you may read it the wrong way ^^. Local space is a coordinate space just like world space is a coordinate space. The vector (0,0,1) is the objects forward vector in its own local space. Of course a vector is just a vector and can be interpreted in any space. However in worldspace the vector (0,0,1) would designate the worlds z axis and would not be related to any object.

In contrast transform.forward returns the objects forward axis in worldspace. That's exactly what my comments said ^^. The first paragraph in the answer actually explain that already, no? This was the whole confusion that the OP had in the first place.

edit
ps: If you have trouble understanding coordinate spaces, vectors and linear algebra, I would highly recommend to watch the 3b1b series on linear algebra.

Answer 2

Answer by Philipp · Mar 06, 2013 at 12:15 PM

Use Transform.TransformDirection / Transform.TransformPoint and Transform.InverseTransformDirection / Transform.InverseTransformPoint!

In your case, you'd use myGameObject.transform.TransformDirection(new Vector3(0,0,1)) to convert a forward direction to a global direction. And InverseTransformDirection to convert back from global to local space.

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Answer 3

Answer by ViktorCor · Nov 19, 2016 at 03:06 PM

Maybe you know?:

How to calculate InverseTransformDirection if you have not transform and have only Vector3(position) and Quartanion(rotation)?

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Converting between local and global direction

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