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Finding the angle between a direction and a point

Discussion in 'Scripting' started by blastone, Sep 19, 2009.

  1. blastone

    blastone

    Joined:
    Apr 7, 2009
    Posts:
    168
    I wish to find the angle (theta) between an objects transform.forward vector and an arbitrary target point.

    Ive tried doing a Vector3.Angle on the transform.forward vector and subtracting that from the Vector3.Angle of the target postiion - the transform position but the numbers seem all skewed.

    I'm using it in a 2d environment.

    Im sure there is a really easy way.. I'm just missing it....
     

    Attached Files:

  2. jcarpay

    jcarpay

    Joined:
    Aug 15, 2008
    Posts:
    514
    Here the math that should get you started
     

    Attached Files:

  3. fallingbrickwork

    fallingbrickwork

    Joined:
    Mar 16, 2009
    Posts:
    1,072
    wouldn't this only be correct if the target point is, in this case on the zero x axis, making the triangle a right angle? I need to do something similar and my trig maths was a long time ago.

    Matt.
     
  4. jcarpay

    jcarpay

    Joined:
    Aug 15, 2008
    Posts:
    514
    If you rotate the right triangle (making it non zero x), it still would be a right triangle. The extra calculations involved are to find the perpendicular distance between the top of the triangle and its foot. For this, dot product is your friend.
     
  5. blastone

    blastone

    Joined:
    Apr 7, 2009
    Posts:
    168
    thanks for the replies, I am down with the trig solution, I was just wondering if there was a smart in built function that I missed.

    I'll google the dot product as well or would projecting the transform onto the target vector suffice....

    Thanks again
     
  6. rozgo

    rozgo

    Joined:
    Feb 7, 2008
    Posts:
    158
    Vector3.Angle should do what you want and Vector3.Cross should give you the axis to rotate around of.
     
  7. blastone

    blastone

    Joined:
    Apr 7, 2009
    Posts:
    168
    Code (csharp):
    1. Vector3 targetDir =m_waypoint.transform.position - transform.position;
    2.         targetDir = targetDir.normalized;
    3.        
    4.         float dot = Vector3.Dot(targetDir, transform.forward);
    5.         float angle = Mathf.Acos( dot ) * Mathf.Rad2Deg;  
    This is what seems to work well for me,
    the angle is always positive, so I also use a cross product


    Code (csharp):
    1. Vector3 normalizedDirection = m_waypoint.transform.position-transform.position;
    2.        
    3.         float whichWay=Vector3.Cross(transform.forward, normalizedDirection).y; //Return left or right?
    To determine if its CW or CCW (ones positive, ones negative above)...

    But after your post rozgo I have indeed found that the Vector.Angle is returning the same result.... and I can use the cross product result to determine direction.

    Cheers!
     
    timbo3DDev44 likes this.
  8. ROCFriesePoort

    ROCFriesePoort

    Joined:
    Mar 27, 2009
    Posts:
    107
    @blastone Thanks for the Vector.Cross, I was looking for some code to determine if a vector is positve or negative. Vector3.Cross did the trick. Thanks!
     
  9. Jack-Wong186

    Jack-Wong186

    Joined:
    Jul 30, 2013
    Posts:
    1
    Thank you! I am searching for this solution too! I am try to implement this to my ai so that it can decide steer left or right, Vector.Cross helps!