physics - Comparing a saved movement with other movement with Kinect

Question

I need to develop an application where a user (physiotherapist) will perform a movement in front of the Kinect, I'll write the data movement in the database and then the patient will try to imitate this motion. The system will calculate the similarity between the movement recorded and executed.

My first idea is, during recording (each 5 second, by example), to store the position (x, y, z) of the points and then compare them in the execution time(by patient).

I know that this approach is too simple, because I imagine that in people of different sizes the skeleton is recognized differently, so the comparison is not reliable.

My question is about the best way to compare a saved motion with a movement executed (on the fly).

Answer 1

I have done this, where a doctors frame is projected onto the patients frame, but with the whole skeleton this doesn't work so well because of different bone heights :/. The code can be found here. It is in beta 2 code, the more current version can be found here, although it is not currently working perfectly

As for comparing, do something like this

for (int i = 0; i < patientList.Count; i++)
{
    int diff = (int)Math.Abs(patientList[i] - doctorList[i]);


    if (diff < 100) //or whatever number you want
    {
         Debug.WriteLine("Good Job");
    }
}

I have abandoned the idea of a whole figure because of the bone heights mentioned by Fixus, so my current program looks some thing like:

EDIT

This is the concept of camparing two movements with kinect and calculate a similarity between the two movements I explain in depth.

Suppose I have the following 2 points, point A (0, 0, 0) and point B (1, 1, 1). Now I want to find the difference from point A to B, so I would subtract all of the X, Y, and Z numbers, so the difference is 1 X 1 Y 1 Z. That is the simple stuff. Now to implement it. The code I have written above, I would implement like this.

//get patient hand coordinates
double patienthandX = Canvas.GetLeft(patienthand);
double patienthandY = Canvas.GetTop(patienthand);

//get doctor hand coordinates
double doctorhandX = Canvas.GetLeft(doctorhand);
double doctorhandY = Canvas.GetTop(doctorhand);

//compare difference for each x and y
//take Absolute value so that it is positive
double diffhandX = Math.Abs(patienthandX - doctorhandX);
double diffhandY = Math.Abs(patienthandY - doctorhandY);

Now here comes another issue. The doctor coordinates are always the same, but what if the patient isn't standing where the doctor coordinates were recorded? Now we implement more simple math. Take this simple example. suppose I want point A(8, 2) to move to point B(4, 12). You multiply the x and y's of A to get to B. So I would multiply the X by .5, and the Y by 6. So for Kinect, I would put a element on the patients hip, then compare this to the doctors hip. Then multiply all of the doctor joints by that number to achieve the doctor joints on top of the patients (more or less). For example

double whatToMultiplyX = (double) doctorhipX / patienthipX;
double whatToMultiplyY = (double) doctorhipY / patienthipY;

This is all pretty simple, but bringing it together is the harder part. So far we, 1) Scale the doctor frames on top of the patient frames, 2) Calculate the difference. 3) Compare the difference throughout the entire rep. and 4) Reset for the next rep. This seems simple but it is not. To calculate the entire difference for the rep, do something like this:

//get patient hand coordinates
double patienthandX = Canvas.GetLeft(patienthand);
double patienthandY = Canvas.GetTop(patienthand);

//get doctor hand coordinates
double doctorhandX = Canvas.GetLeft(doctorhand);
double doctorhandY = Canvas.GetTop(doctorhand);

//compare difference for each x and y
//take Absolute value so that it is positive
double diffhandX = Math.Abs(patienthandX - doctorhandX);
double diffhandY = Math.Abs(patienthandY - doctrorhandY);

//+= so that it keeps adding to it.
totaldiffhandX += diffhandX;
totaldiffhandY += diffhandY;

Now we can compare, and say:

if (totaldiffhandX < 1000 && totaldiffhandY < 1000) //keep numbers pretty high since it is an entire rep
{
     //reset difference
     totaldiffhandX = 0;
     totaldiffhandY = 0;

     //tell the patient good job
     Debug.WriteLine("Good Job");
}

This is pretty easy, but keep in mind you must do this for every single joint's x and y. Otherwise it will not work. Hope this Helps.