Elbow location and hand center of mass?

[Robert_Oschler]

In the PercSDK the GeoNode data returned the elbow location and the hand center of mass.  How do I get that information with the RealSense SDK?

I did a full search in the reference manual for elbow and couldn't find anything.

Thanks,

Robert

[MartyG]

The RealSense SDK treats any large round joint on the body as a hand center-point.  This is why you can control objects with your knee if you roll up the leg of your pants and wave it in front of the camera.  So if you define your object to track the hand center and point your elbow at the camera, in theory it should move the object.  

Of course, you don't want the camera to read your actual hand-center at the same time and get confused.  So you would have to keep your hands outside of the view of the camera lens (e.g by holding your hands up in the air).

[Robert_Oschler]

Hi Marty,

I don't want to track the elbow per se, but to use it as a fulcrum point to calculate against the hand's center (or center of mass in the old PercSDK).  Then I can calculate the angle more easily when the user does a "wax on/wax off" kind of gesture.  Imagine the elbow planted on the desk and the user rotating their arm like a windshield wiper blade.  Calculating that angle is much easier than trying to do the same by calculating the angle of the fingers to the center of the palm.

Did Intel take it out of the RealSense SDK (or never put it in)?  I'll be greatly saddened if they did.  It was a very useful measurement even it if was a few inches off from the elbow because it was still always a large distance from the palm and directly on the forearm itself, making it very useful for the angle calculation I mention above.

Thanks,
Robert

[MartyG]

I guess I'm spoiled by Unity, whose RealSense scripts work all this kind of thing out pretty much automatically.  I have big respect for people who try to program this stuff manually from scratch!

Yeah, I can see how it would be easier to work out the angle if you were tracking the elbow.  Perhaps you would have more luck tracking the wrist joint instead of the center-point.  Because if you think about it, the wrist is fixed to the elbow and so it's impossible for the elbow to tip left and right unless the wrist is doing so as well.  So the wrist could be your fulcrum instead of the elbow.

[Robert_Oschler]

Any point that is not close to the fulcrum.  The wrist is too close to the fingers and moves almost in lock-step, making the determination of any angular movement very difficult.