Object height using Kinect

Question

For example, I am standing in-front of my Kinect. The Kinect can identify the joints, and it will expose them as a data structure. Till this point I am clear.

So, can we define the height as the difference between Head joint - ((LeftAnkle + RightAnkle)/2)?

I have tried trigonometric formulas, but there are two problems I am facing. One is identifying the person in the view. The second one is identifying the exact positions of Top of head and bottom of foot.

I have tried the point cloud, but got lost in how to generate the point cloud specific to a person. I mean without including the background objects.

Please suggest some ideas about how I can calculate the height of a person using the Kinect?

Answer 1

You can convert the Head Joint into global coordinate system. There is no need to do any math. The y coordinate in global coordinate will be his height.

All you need to do is check what pixel the head joint is and convert the pixel + depth informations into word coordinate space in mm.

I don't know what API you are using, but if it's being capable to segment a human and return his joint's, probably you are using OpenNI/NITE or Microsoft SDK. Both of them have a function that converts a pixel + depth coordinate into a x,y,z in mm. I don't know exactly what are the functions but their names would be something like : depth_to_mm, or disparity_to_mm. You need to check both documentations to find it, or you can do it by yourself. This site have informations on how to convert depth to mm: http://nicolas.burrus.name/index.php/Research/KinectCalibration

Answer 2

I have extracted the two points - Head and Left foot (or Right Foot), then i found the euclidean distance between these points gave the distance with 4 inch variation. My test results are satisfactory, so we are using this approach as temporary work around.