c++ - Principle range of object orientation using image moments -


i trying extract angle of shape in image using moments in opencv/c++. able extract angle, issue principal range of angle 180 degrees. makes orientation of object ambiguous respect 180 degree rotations. code using extract angle is,

findcontours(frame, contours, cv_retr_external, cv_chain_approx_simple);  vector<vector<point2i> > hull(contours.size());  int maxarea = 0; int maxi = -1;  int m20 = 0; int m02 = 0; int m11 = 0;  (int = 0; < contours.size(); i++) {     convexhull(contours[i], hull[i], false);     approxpolydp(hull[i], contourvertices, arclength(hull[i], true)*0.1, true);     shapemoments = moments(hull[i], false);      if(shapemoments.m00 <= areathreshold || shapemoments.m00 >= max_area)         continue;      if(contourvertices.size() <= 3 || contourvertices.size() >= 7)         continue;      if(shapemoments.m00 >= maxarea)     {         maxarea = shapemoments.m00;         maxi = i;     } }  if(maxi == -1)     return false;  fabriccontour = hull[maxi];  approxpolydp(hull[maxi], contourvertices, arclength(hull[maxi], true)*0.02,true); shapemoments = moments(hull[maxi], false); centerofmass = point2f(shapemoments.m10/shapemoments.m00, shapemoments.m01/shapemoments.m00);  drawcontours(contourframe, hull, maxi, scalar(24, 35, 140), cv_filled, cv_aa); drawcontours(originalframe, hull, maxi, scalar(255, 0, 0), 8, cv_aa); circle(contourframe, centerofmass, 4, scalar(0, 0, 0), 10, 8, 0);  posx = centerofmass.x; posy = centerofmass.y; m11 = shapemoments.mu11/shapemoments.m00; m20 = shapemoments.mu20/shapemoments.m00; m02 = shapemoments.mu02/shapemoments.m00; num = double(2)*m11; den = m20 - m02; angle = (int(-1*(180/(2*m_pi))*atan2(num, den)) + 45 + 180)%180; //angle = int(-1*(180/(2*m_pi))*atan2(num, den));  area = shapemoments.m00;

is there way can remove ambiguity extracted angle? tries using third order moments, not seem reliable.


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