CODEWITHSUNDEEP
c++opencv
user1583647
user1583647

Reputation: 1245

Finding min and max of a point vector

I want to find the min and max value from a point vector. The vector consists of x and y element type. I want the min and max of x and the minmax of y. My vector is defined as:

 std::vector<cv::Point> location;
findNOZeroInMat(angles,location);

//I tried to use but it gives an error
  minMaxLoc(location.cols(0), &minVal_x, &maxVal_x);
    minMaxLoc(location.cols(1), &minVal_y, &maxVal_y);

I tried location.x too but it didn't work. How can I get the min and max value of x and y seperately?

Upvotes: 2

Views: 8065

Answers (2)

luator
luator

Reputation: 5027

cv::boundingRect is doing what you want. It

Calculates the up-right bounding rectangle of a point set.

The result is of type cv::Rect which has attributes x, y, width, heigth but also provides methods tl (= top left corner) and br (= bottom right corner) which can be used to find desired min. and max. values. Note that tl is inclusive but bt is exclusive.

std::vector<cv::Point> points;
// do something to fill points...

cv::Rect rect = cv::boundingRect(points);

// tl() directly equals to the desired min. values
cv::Point minVal = rect.tl();

// br() is exclusive so we need to subtract 1 to get the max. values
cv::Point maxVal = rect.br() - cv::Point(1, 1);

Upvotes: 5

juanchopanza
juanchopanza

Reputation: 227498

You can use std::minmax_element with custom less-than comparison functions/functors:

#include <algorithm>

bool less_by_x(const cv::Point& lhs, const cv::Point& rhs)
{
  return lhs.x < rhs.x;
}

Then

auto mmx = std::minmax_element(location.begin(), location.end(), less_by_x);

and similarly for y. mmx.first will have an iterator to the minimum element, and mmx.second to the maximum one.

If you don't have C++11 support for auto you need to be explicit:

typedef std::vector<cv::Point>::const_iterator PointIt;
std::pair<PointIt, PointIt> mmx = std::minmax_element(location.begin(), 
                                                      location.end(), 
                                                      less_by_x);

but note that std::minmax_element requires C++11 library support.

Upvotes: 9

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