Do the HoughLines or HoughLinesP functions in OpenCV return the list of lines in accumulator order like the HoughCircles function does? I would like to know the ordering of lines. It would also be very handy to get a the accumulator value for the lines so an intelligent and adaptive threshold could be used instead of a fixed one. Are either the ordering or the accumulator value available without rewriting OpenCV myself?
HoughTransform orders lines descending by number of votes. You can see the code here
However, the vote count is lost as the function returns - the only way to have it is to modify OpenCV.
The good news is that is not very complicated - I did it myself once. It's a metter of minutes to change the output from vector< Vec2f > to vector< Vec3f > and populate the last param with vote count.
Also, you have to modify CvLinePolar to add the third parameter - hough is implemented in C, and there is a wrapper over it in C++, so you have to modify both the implementation and the wrapper.
The main code to modify is here
for( i = 0; i < linesMax; i++ )
{
CvLinePolar line;
int idx = sort_buf[i];
int n = cvFloor(idx*scale) - 1;
int r = idx - (n+1)*(numrho+2) - 1;
line.rho = (r - (numrho - 1)*0.5f) * rho;
line.angle = n * theta;
// add this line, and a field voteCount to CvLinePolar
// DO NOT FORGET TO MODIFY THE C++ WRAPPER
line.voteCount = accum[idx];
cvSeqPush( lines, &line );
}