Getting vector which is pointing to the right/left of a direction vector?

Question

If I have a vector such as (0,0,1) and I get its 'right' equivalent I should get something like (1,0,0), its left would be (-1,0,0), this is just the simplest case there may be more complex scenarios such as (0.2, 0.3, 0.5), so on and so forth.

Any ideas?

Answer 1

Answer by aldonaletto · Mar 16, 2012 at 01:51 PM

In a 2D space - Vector2, or Vector3 with one coordinate fixed at 0 - you can get the right and left vectors with simple transformations:

  // original vector in the xz plane (y = 0):
  var forward: Vector3 = Vector3(0.5, 0.0, 0.8);
  // transformed vectors right and left:
  var right = Vector3(forward.z, forward.y, -forward.x);
  var left = -right;

For a full 3D vector, however, there's no predefined left/right directions - you must set some reference, usually the up direction. Having the up direction, you can calculate the right and left vectors using a cross product:

  // original vector:
  var forward: Vector3 = Vector3(0.5, 0.7, 0.8);
  // up direction:
  var up: Vector3 = Vector3(0.0, 1.0, 0.0);
  // find right vector:
  var right = Vector3.Cross(forward.normalized, up.normalized);
  var left = -right;

NOTE: I never remember the correct order of the Cross parameters; if the right vector is pointing to the left, just swap the parameters.

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IntergalacticSloth · Oct 07, 2016 at 10:57 PM 0

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Thumb first!

Speaking of "The Left Hand Rule", the Vector Cross function takes the thumb parameter first. So I think your left and right are backwards :P

TEST: I threw this pretty little mess into an Update() of a script in order to check.

I also clicked 'Collapse' in the console... Played for a second, then stopped to read the console :P

         Debug.Log("We feed the cross 'Up' then 'Forward' and get: " 
             + "\n" 
             + Vector3.Cross(Vector3.up, Vector3.forward));
         Debug.Log("Now look! The world's 'Right' is also Vector: " 
             + "\n" 
             + Vector3.right);
         Debug.Log("Just as you would expect from your left hand." 
             + "\n");
         Debug.Log("What if we feed 'Forward' first, as the ''thumb''?" 
             + "\n");
         Debug.Log("Awkward hand position, but you get: " 
             + "\n" 
             + Vector3.Cross(Vector3.forward, Vector3.up));

Answer 2

Getting vector which is pointing to the right/left of a direction vector?

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