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So you have the lengths of the detected segments. Now you need to filter them. For example you can create a function that for an input vector<vec4i> it returns another vector<vec4i> that has just the lines longer than a parameter:

std::vector<cv::vec4i> filterLinesByLen(const std::vector<cv::vec4i>& lines, double minLen)
{
std::vector<cv::vec4i> longLines;
for (cv::vec4i line : lines)
{   if (euclidDist(line) >= minLen) { longLines.push_back(line); }    }
return longLines;
}


So you have the lengths of the detected segments. Now you need to filter them. For example you can create a function that for an input vector<vec4i> it returns another vector<vec4i> that has just the lines longer than a parameter:

std::vector<cv::vec4i> std::vector<cv::Vec4i> filterLinesByLen(const std::vector<cv::vec4i>& std::vector<cv::Vec4i>& lines, double minLen)
{
std::vector<cv::vec4i> longLines;
for (cv::vec4i (cv::Vec4i line : lines)
{   if (euclidDist(line) >= minLen) { longLines.push_back(line); }    }
return longLines;
}


the eucldian distance shoud be something like:

double euclidDist(const cv::Vec4i& line)
{
return std::sqtr(static_cast<double>((line[0] - line[2]) * (line[0] - line[2]) + (line[1] - line[3]) * (line[1] - line[3])));
}


So you have the lengths of the detected segments. Now you need to filter them. For example you can create a function that for an input vector<vec4i> it returns another vector<vec4i> that has just the lines longer than a parameter:

std::vector<cv::Vec4i> filterLinesByLen(const std::vector<cv::Vec4i>& lines, double minLen)
{
std::vector<cv::vec4i> longLines;
for (cv::Vec4i line : lines)
{   if (euclidDist(line) >= minLen) { longLines.push_back(line); }    }
return longLines;
}


the eucldian distance shoud be something like:

double euclidDist(const cv::Vec4i& line)
{
return std::sqtr(static_cast<double>((line[0] - line[2]) * (line[0] - line[2]) + (line[1] - line[3]) * (line[1] - line[3])));
}


In your code you shall do something like this

std::vector<cv::Vec4i> longLines = filterLinesByLen(lines, 80); // you can replace 80 by a value that you think is good, or create a function that returns the mean of the lenghts ...