How to move a kinect skeleton to another position

Question

I am working on a extension method to move one skeleton to a desired position in the kinect field os view.

My code receives a skeleton to be moved and the destiny position, i calculate the distance between the received skeleton hip center and the destiny position to find how much to move, then a iterate in the joint applying this factor. My code, actualy looks like this.

public static Skeleton MoveTo(this Skeleton skToBeMoved, Vector4 destiny)
    {
        Joint newJoint = new Joint();

        ///Based on the HipCenter (i dont know if it is reliable, seems it is.)
        float howMuchMoveToX = Math.Abs(skToBeMoved.Joints[JointType.HipCenter].Position.X - destiny.X);
        float howMuchMoveToY = Math.Abs(skToBeMoved.Joints[JointType.HipCenter].Position.Y - destiny.Y);
        float howMuchMoveToZ = Math.Abs(skToBeMoved.Joints[JointType.HipCenter].Position.Z - destiny.Z);
        float howMuchToMultiply = 1;

        // Iterate in the 20 Joints
        foreach (JointType item in Enum.GetValues(typeof(JointType)))
        {
            newJoint = skToBeMoved.Joints[item];

            // This adjust, try to keeps the skToBeMoved in the desired position
            if (newJoint.Position.X < 0)
                howMuchToMultiply = 1; // if the point is in a negative position, carry it to a "more positive" position
            else
                howMuchToMultiply = -1; // if the point is in a positive position, carry it to a "more negative" position

            // applying the new values to the joint
            SkeletonPoint pos = new SkeletonPoint()
            {
                X = newJoint.Position.X + (howMuchMoveToX * howMuchToMultiply),
                Y = newJoint.Position.Y, // * (float)whatToMultiplyY,
                Z = newJoint.Position.Z, // * (float)whatToMultiplyZ
            };

            newJoint.Position = pos;
            skToBeMoved.Joints[item] = newJoint;

            //if (skToBeMoved.Joints[JointType.HipCenter].Position.X < 0)
            //{
            //    if (item == JointType.HandLeft)
            //    {
            //        if (skToBeMoved.Joints[item].Position.X > 0)
            //        {

            //        }
            //    }
            //}
        }

        return skToBeMoved;
    }

Actualy, only X position is considered.

Now, THE PROBLEM:

If i stand in a negative position, and move my hand to a positive position, a have a strange behavior, look this image

enter image description here

To reproduce this behaviour you could use this code

using (SkeletonFrame frame = e.OpenSkeletonFrame())
        {
            if (frame == null)
                return new Skeleton();

            if (skeletons == null || skeletons.Length != frame.SkeletonArrayLength)
            {
                skeletons = new Skeleton[frame.SkeletonArrayLength];
            }
            frame.CopySkeletonDataTo(skeletons);

            Skeleton skeletonToTest = skeletons.Where(s => s.TrackingState == SkeletonTrackingState.Tracked).FirstOrDefault();

            Vector4 newPosition = new Vector4();
            newPosition.X = -0.03412333f;
            newPosition.Y = 0.0407479f;
            newPosition.Z = 1.927342f;
            newPosition.W = 0; // ignored

            skeletonToTest.MoveTo(newPosition);
        }

I know, this is simple math, but i cant figure it out why this is happen. Any help will be apreciated.

it should be a matter of adding the new position translation vector to each joint position in the skeleton and nothing more — George Profenza, Nov 25 '12 at 16:43
@George Profenza Yes, it is! Whats your code modifications to solve it? — Ewerton, Nov 25 '12 at 17:52
Glad you sorted out, I was out when you replied. Still, from my point of view, if `Vector4 destiny` is a relative position to translate towards it's just a matter doing doing someting like `currentPositionVector += translationVector`(in pseudo, as in, `currentJoint.x += newPos.x`,same for y and z). If `destiny is absolute`, you would use the difference between the current position and the new position. The part that puzzles me in your approach is why you flip (multiply by -1) the difference vector. Also, when you get the difference vector, you seem to only add the to the X component... — George Profenza, Nov 26 '12 at 00:24
...I haven't used the Kinect SDK much, are the skeleton positions 3D positions in relation to the kinect or converted 2D screen coordinates ?`Y = newJoint.Position.Y + (0)` and same for Z wouldn't change those coordinates. — George Profenza, Nov 26 '12 at 00:25

Ewerton · Accepted Answer · 2012-11-26T15:15:08.710

Problem solved. This is the code

public static Skeleton MoveTo(this Skeleton skToBeMoved, Vector4 destiny)
    {
        Joint newJoint = new Joint();

        ///Based on the HipCenter (i dont know if it is reliable, seems it is.)
        float howMuchMoveToX = (skToBeMoved.Joints[JointType.HipCenter].Position.X - destiny.X) * -1;
        float howMuchMoveToY = (skToBeMoved.Joints[JointType.HipCenter].Position.Y - destiny.Y) * -1;
        float howMuchMoveToZ = (skToBeMoved.Joints[JointType.HipCenter].Position.Z - destiny.Z) * -1;

        // Iterate in the 20 Joints
        foreach (JointType item in Enum.GetValues(typeof(JointType)))
        {
            newJoint = skToBeMoved.Joints[item];

            // applying the new values to the joint
            SkeletonPoint pos = new SkeletonPoint()
            {
                X = (float)(newJoint.Position.X + (howMuchMoveToX)),
                Y = (float)(newJoint.Position.Y + (howMuchMoveToY)),
                Z = (float)(newJoint.Position.Z + (howMuchMoveToZ))
            };

            newJoint.Position = pos;
            skToBeMoved.Joints[item] = newJoint;
        }

        return skToBeMoved;
    }

How to move a kinect skeleton to another position

1 Answers1

Linked