using DateTime and Stopwatch to calculate velocity with kinect sdk - kinect

Question

i'm stuck for days to calculate the velocity of a mouvement so i'll try to more explain my problem.
i have to applicate an approache which allows to detect fall with kinect SDK and VS c#.
this approche takes as input 3 dimensions of a 3Box, built from the coordinates of skeleton joints.
these dimensions are:
W = |xMin - xMax|;
H = |yMin - yMax|;
D = |zMin - zMax|;
with xMin, xMax, yMin, yMax, zMin, zMax the minimum and the maximum of coordinates in all the tracked joints.
At this point, this is not the problem.. i already calculated all these values:
List<Joint> JointList = new List<Joint>();
List<double> JCx = new List<double>();
List<double> JCy = new List<double>();
List<double> JCz = new List<double>();
// define the min and max of coordinates as the filed of view of kinect
private double xMin = 2.2;
private double xMax = -2.2;
private int framecounter = 0;
private double yMin = 1.6;
private double yMax = -1.6;
private double zMin = 4;
private double zMax = 0;
Skeleton first = GetFirstSkeleton(allFramesReadyEventArgs);
if (first == null) // if no skeleton
{
txtP.Text = "No One";
return;
}
else
{
txtP.Text = "Yes";
skeletonDetected = true;
/// define all joints
Joint Head = first.Joints[JointType.Head];
JointList.Add(Head);
Joint SC = first.Joints[JointType.ShoulderCenter];
JointList.Add(SC);
Joint SL = first.Joints[JointType.ShoulderLeft];
JointList.Add(SL);
Joint SR = first.Joints[JointType.ShoulderRight];
JointList.Add(SR);
Joint EL = first.Joints[JointType.ElbowLeft];
JointList.Add(EL);
Joint ER = first.Joints[JointType.ElbowRight];
JointList.Add(ER);
Joint WL = first.Joints[JointType.WristLeft];
JointList.Add(WL);
Joint WR = first.Joints[JointType.WristRight];
JointList.Add(WR);
Joint HandL = first.Joints[JointType.HandLeft];
JointList.Add(HandL);
Joint HandR = first.Joints[JointType.HandRight];
JointList.Add(HandR);
Joint Spine = first.Joints[JointType.Spine];
JointList.Add(Spine);
Joint HipC = first.Joints[JointType.HipCenter];
JointList.Add(HipC);
Joint HipL = first.Joints[JointType.HipLeft];
JointList.Add(HipL);
Joint HipR = first.Joints[JointType.HipRight];
JointList.Add(HipR);
Joint KL = first.Joints[JointType.KneeLeft];
JointList.Add(KL);
Joint KR = first.Joints[JointType.KneeRight];
JointList.Add(KR);
Joint AnkL = first.Joints[JointType.AnkleLeft];
JointList.Add(AnkL);
Joint AnkR = first.Joints[JointType.AnkleRight];
JointList.Add(AnkR);
Joint FL = first.Joints[JointType.FootLeft];
JointList.Add(FL);
Joint FR = first.Joints[JointType.FootRight];
JointList.Add(FR);
// calculate x, y and z coordinates for each joint and
// put it into 3 different lists
foreach (Joint j in JointList)
{
if (j.TrackingState == JointTrackingState.Tracked)
jx = j.Position.X;
JCx.Add(jx);
jy = j.Position.Y;
JCy.Add(jy);
jz = j.Position.Z;
JCz.Add(jz);
foreach (double f in JCx)
{
if (f < xMin)
xMin = f;
else if (f > xMax)
xMax = f;
}
foreach (double f in JCy)
{
if (f < yMin)
yMin = f;
else if (f > yMax)
yMax = f;
}
foreach (double f in JCz)
{
if (f < zMin)
zMin = f;
else if (f > zMax)
zMax = f;
}
}
txtminx.Text = xMin.ToString();
txtmaxx.Text = xMax.ToString();
txtminy.Text = yMin.ToString();
txtmaxy.Text = yMax.ToString();
txtminz.Text = zMin.ToString();
txtmaxz.Text = zMax.ToString();
//calculate the 3 dimensions of the Box and the diagonal WD
double W = System.Math.Abs(xMin - xMax);
double H = System.Math.Abs(yMin - yMax);
double D = System.Math.Abs(zMin - zMax);
double WD = System.Math.Sqrt(Math.Pow(W0, 2) + Math.Pow(D0, 2));
The problem is when i have to calculate the velocity of the box dimensions vH and vWD .
vH = (Hi - H0) /(Ti- T0);
vWD = (WDi- WD0) /(Ti-T0);
i tried to use DateTime.UtcNow and Stopwatch to calculate the time spend
DateTime T0 = DateTime.UtcNow;
Stopwatch _stopwatch = Stopwatch.StartNew();
DateTime Ti = DateTime.UtcNow;
but i don't know how to get H value in a first time and in a second also i'm not sure if this methode will give me real result.
Can anyone help me ?
Thanks in advance

Answer 1

I did something similar in an application.
I started a StopWatch when the application started:
System.Diagnostics.Stopwatch stopWatch = new System.Diagnostics.Stopwatch();
int msNow;
int msPast;
int dif;
TimeSpan currentTime;
TimeSpan lastTime = new TimeSpan(0);
public GaitAnalyzer()
{
stopWatch.Start();
}
Then you just have to do something like this:
currentTime = stopWatch.Elapsed;
msNow = currentTime.Seconds * 1000 + currentTime.Milliseconds;
if(lastTime.Ticks != 0)
{
msPast = lastTime.Seconds * 1000 + lastTime.Milliseconds;
dif = msNow - msPast;
}
lastTime = currentTime;