Body joints angle using Kinect

http://stackoverflow.com/questions/12608734/body-joints-angle-using-kinect-checking-time-interval?rq=1
http://stackoverflow.com/questions/15989322/calculate-kinect-skeleton-knee-and-elbow-angles-using-existing-joint-angles
http://channel9.msdn.com/coding4fun/kinect/Kinect-Earth-Move
http://social.msdn.microsoft.com/Forums/en-US/8516bab7-c28b-4834-82c9-b3ef911cd1f7/using-kinect-to-calculate-angles-between-human-body-joints
public static double myMethodZY(Joint j1, Joint j2, Joint j3)

    {

        Vector3 a = new Vector3(0, j1.Position.Y- j2.Position.Y, j1.Position.Z- j2.Position.Z);

        Vector3 b = new Vector3(0, j3.Position.Y - j2.Position.Y, j3.Position.Z - j2.Position.Z);

        a.Normalize();

        b.Normalize();

        double dotProduct = Vector3.Dot(a,b);

        double angle= Math.Acos(dotProduct);

        angle =  angle * 180 / Math.PI;

        //angle = 180 - angle;

        return angle;

    }

f you are using Kinect SDK to get the skeletal tracking, the you can use this:

/// <summary>/// Return the angle between 3 Joints/// Regresa el ángulo interno dadas 3 Joints/// </summary>/// <param name="j1"></param>/// <param name="j2"></param>/// <param name="j3"></param>/// <returns></returns>publicstaticdoubleAngleBetweenJoints(Joint j1,Joint j2,Joint j3){doubleAngulo=0;double shrhX = j1.Position.X - j2.Position.X;double shrhY = j1.Position.Y - j2.Position.Y;double shrhZ = j1.Position.Z - j2.Position.Z;double hsl = vectorNorm(shrhX, shrhY, shrhZ);double unrhX = j3.Position.X - j2.Position.X;double unrhY = j3.Position.Y - j2.Position.Y;double unrhZ =j3.Position.Z - j2.Position.Z;double hul = vectorNorm(unrhX, unrhY, unrhZ);double mhshu = shrhX * unrhX + shrhY * unrhY + shrhZ * unrhZ;double x = mhshu /(hul * hsl);if(x !=Double.NaN){if(-1<= x && x <=1){double angleRad =Math.Acos(x);Angulo= angleRad *(180.0/Math.PI);}elseAngulo=0;}elseAngulo=0;returnAngulo;}/// <summary>/// Euclidean norm of 3-component Vector/// </summary>/// <param name="x"></param>/// <param name="y"></param>/// <param name="z"></param>/// <returns></returns>privatestaticdouble vectorNorm(double x,double y,double z){returnMath.Sqrt(Math.Pow(x,2)+Math.Pow(y,2)+Math.Pow(z,2));}

This method use 3 joints to get an angle.

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