use k-curvature to detect hand gesture. reference: http://www.tmroyal.com/a-high-level-description-of-two-fingertip-tracking-techniques-k-curvature-and-convexity-defects.html http://www.mathworks.com/matlabcentral/fileexchange/32696-2d-line-curvature-and-normals http://stackoverflow.com/questions/14631776/calculate-turning-points-pivot-points-in-trajectory-path http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=7359032&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel7%2F7322101%2F7358979%2F07359032.pdf%3Farnumber%3D7359032
