Kinect-Matlab: Get joint angle information

Question

I am a beginner at kinect and I want to use it with matlab. I need joint angle information out of the skeleton data. What is the easiest way to do this? Thanks.

Answer 1

I am not good with Mat lab, but try to use c# with Visual Studio. Use the SkeletonBasics-WPF in the Microsoft SDK´s as a template to add this code:

public class Angles
    {
    public double AngleBetweenTwoVectors(Vector3D vectorA, Vector3D vectorB)
        {
            double dotProduct;
            vectorA.Normalize();
            vectorB.Normalize();
            dotProduct = Vector3D.DotProduct(vectorA, vectorB);

            return (double)Math.Acos(dotProduct)/Math.PI*180;
        }

        public byte[] GetVector(Skeleton skeleton)
        {
            Vector3D ShoulderCenter = new Vector3D(skeleton.Joints[JointType.ShoulderCenter].Position.X, skeleton.Joints[JointType.ShoulderCenter].Position.Y, skeleton.Joints[JointType.ShoulderCenter].Position.Z);
            Vector3D RightShoulder = new Vector3D(skeleton.Joints[JointType.ShoulderRight].Position.X, skeleton.Joints[JointType.ShoulderRight].Position.Y, skeleton.Joints[JointType.ShoulderRight].Position.Z);
            Vector3D LeftShoulder = new Vector3D(skeleton.Joints[JointType.ShoulderLeft].Position.X, skeleton.Joints[JointType.ShoulderLeft].Position.Y, skeleton.Joints[JointType.ShoulderLeft].Position.Z);
            Vector3D RightElbow = new Vector3D(skeleton.Joints[JointType.ElbowRight].Position.X, skeleton.Joints[JointType.ElbowRight].Position.Y, skeleton.Joints[JointType.ElbowRight].Position.Z);
            Vector3D LeftElbow = new Vector3D(skeleton.Joints[JointType.ElbowLeft].Position.X, skeleton.Joints[JointType.ElbowLeft].Position.Y, skeleton.Joints[JointType.ElbowLeft].Position.Z);
            Vector3D RightWrist = new Vector3D(skeleton.Joints[JointType.WristRight].Position.X, skeleton.Joints[JointType.WristRight].Position.Y, skeleton.Joints[JointType.WristRight].Position.Z);
            Vector3D LeftWrist = new Vector3D(skeleton.Joints[JointType.WristLeft].Position.X, skeleton.Joints[JointType.WristLeft].Position.Y, skeleton.Joints[JointType.WristLeft].Position.Z);
            Vector3D UpVector = new Vector3D(0.0, 1.0, 0.0);

            double AngleRightElbow = AngleBetweenTwoVectors(RightElbow - RightShoulder, RightElbow - RightWrist);
            double AngleRightShoulder = AngleBetweenTwoVectors(UpVector, RightShoulder - RightElbow);
            double AngleLeftElbow = AngleBetweenTwoVectors(LeftElbow - LeftShoulder, LeftElbow - LeftWrist);
            double AngleLeftShoulder = AngleBetweenTwoVectors(UpVector, LeftShoulder - LeftElbow);


            byte[] Angles = {Convert.ToByte(AngleRightElbow), Convert.ToByte(AngleRightShoulder),Convert.ToByte(AngleLeftElbow),Convert.ToByte(AngleLeftShoulder)};
            return Angles;
        }
}

Insert this at the top. Call the GetVector() method here:

 private void SensorSkeletonFrameReady(object sender, SkeletonFrameReadyEventArgs e)
        {

            Skeleton[] skeletons = new Skeleton[0];

            using (SkeletonFrame skeletonFrame = e.OpenSkeletonFrame())
            {
                if (skeletonFrame != null)
                {
                    skeletons = new Skeleton[skeletonFrame.SkeletonArrayLength];
                    skeletonFrame.CopySkeletonDataTo(skeletons);

                }
            }

            using (DrawingContext dc = this.drawingGroup.Open())
            {
                // Draw a transparent background to set the render size
                dc.DrawRectangle(Brushes.Black, null, new Rect(0.0, 0.0, RenderWidth, RenderHeight));

                if (skeletons.Length != 0)
                {
                    foreach (Skeleton skel in skeletons)
                    {
                        RenderClippedEdges(skel, dc);

                        if (skel.TrackingState == SkeletonTrackingState.Tracked)
                        {
                            this.DrawBonesAndJoints(skel, dc);
                            Angles MyAngles = new Angles();
                            byte[] ReadyAngles = MyAngles.GetVector(skel);
                            RightElbow.Text = ReadyAngles[0].ToString();
                            RightShoulder.Text = ReadyAngles[1].ToString();
                            LeftElbow.Text = ReadyAngles[2].ToString();
                            LeftShoulder.Text = ReadyAngles[3].ToString();
                            byte[] SequenceStart = {255};

                            if (ArduinoPort.IsOpen)
                            {
                                ArduinoPort.Write(SequenceStart,0,1);
                                ArduinoPort.Write(ReadyAngles, 0, 4);
                            }
                        }
                        else if (skel.TrackingState == SkeletonTrackingState.PositionOnly)
                        {
                            dc.DrawEllipse(
                            this.centerPointBrush,
                            null,
                            this.SkeletonPointToScreen(skel.Position),
                            BodyCenterThickness,
                            BodyCenterThickness);
                        }
                    }
                }

                // prevent drawing outside of our render area
                this.drawingGroup.ClipGeometry = new RectangleGeometry(new Rect(0.0, 0.0, RenderWidth, RenderHeight));
            }
        }

As you can see I added 4 textboxes as I am calculating 4 Angles (RS, LF, RE, LE). These Angles are being passed to the textbox in my .xaml file. I hope this works for you.

Answer 2

You would need the Image Acquisition Toolbox, which includes support for Kinect including skeleton data.