Angle detection of human body joints

Hai. I want to know how am I going to find an angle of human body joints such as angle of elbow, hip, knee and etc. The process of my project:

1. Capture an image of human riding a bicycle 2. Use canny edge detection to have the outer lines of human body 3. Draw the line intersection of the joints. 4. Find the angle of the joints from the intersection lines

The problem i am facing now is that i don't know how to create the lines and finding the angles to be displayed using GUI. Did my steps up there are true? Can anyone help me with this?

[Gorkem Tanriverdi]

I have a project that I need to detec all proporties and dimensions of human body from video may be later I will use these datas for gait tracking, but at first project is about just getting these datas, are there anybody here to assist? I will appreciate him:)