The signed angle between two Vector3D points

Report · Apr 17, 2012

Hi,

Can someone show me how to get the signed angle between two Vector3D points?

Thanks!

Report · Apr 18, 2012

the Vector3D class has a function called angleBtween() does that not do what you want? not it returns an angle in radians

Report · Apr 18, 2012

Hi _spodboyle,

That returns an unsigned angle. A signed angle returns a minus or positive angle depending on which side one vector is compared to the other.

Report · Apr 18, 2012

This might help:

http://www.kirupa.com/forum/showthread.php?356815-Vector3D-angleBetween-getting-signed-angles

Report · Apr 18, 2012

Hi Sinious,

that looks promising. I wish that the formula was written out, I'm not sure I understand what the responder in that post is saying : (

Report · Apr 18, 2012

here is a pseudo solution

http://stackoverflow.com/questions/5188561/signed-angle-between-two-3d-vectors-with-same-origin-with...

Report · Apr 18, 2012

Hi _spoboyle,

That looks helpful. How do I get Vn?

Report · Apr 18, 2012

well this is the bit I don't really understand

Vn is the normal to the plane containing Va and Vb. You could find Vn by calculating the normalised corssproduct of Va and Vb

Report · Apr 18, 2012

I've just tried what i said above and it's didn't give me what i expected

here is another discussion

http://www.physicsforums.com/showthread.php?t=262649

Report · Apr 18, 2012

I don't fully understand it or even how you would use it but here is an example I wrote in AS3

package
{
          import flash.display.Sprite;
          import flash.events.Event;
          import flash.geom.Vector3D;
  
          public class Main extends Sprite
          {
                    public function Main():void
                    {
                              if (stage)
                              {
                                        init();
                              }
                              else
                              {
                                        addEventListener(Event.ADDED_TO_STAGE, init);
                              }
                    }
  
                    public function init(e:Event = null):void
                    {
                              removeEventListener(Event.ADDED_TO_STAGE, init);
  
                              var a:Vector3D = new Vector3D(2, 1, 3);
                              a.normalize();
                              var b:Vector3D = new Vector3D(1, 2, 3);
                              b.normalize();
  
                              var sina:Number = a.crossProduct(b).length / (a.length * b.length);
                              var cosa:Number = a.dotProduct(b) / (a.length * b.length);
  
                              var sinb:Number = b.crossProduct(a).length / (a.length * b.length);
                              var cosb:Number = b.dotProduct(a) / (a.length * b.length);
  
                              var radiansa:Number = Math.atan2(sina, cosa);
                              var radiansb:Number = Math.atan2(sinb, cosb);
  
                              var n:Vector3D = a.crossProduct(b);
                              n.normalize();
  
                              var signa:Number = n.dotProduct(a.crossProduct(b));
                              var signb:Number = n.dotProduct(b.crossProduct(a));
  
                              if (signa < 0)
                              {
                                        radiansa = -radiansa;
                              }
  
                              if (signb < 0)
                              {
                                        radiansb = -radiansb;
                              }
  
                              var degreesa:Number = radiansa * 180 / Math.PI;
                              trace("angle A to B: " + degreesa);
  
                              var degreesb:Number = radiansb * 180 / Math.PI;
                              trace("angle B to A: " + degreesb);
  
                    }
          }
}

Report · Apr 18, 2012

that looks promising.

Thanks!