如何使用 magnitude 和 absdiff OpenCV 函数来计算距离？

Question

如何使用 magnitude 和 absdiff？我看了the documentation里面的解释，但是每次都报错，因为我不明白到底应该怎么输入数组和输出。应该是 vector、Mat 还是 Scalar？我尝试了一些但我失败了，与 cartToPolar 一样。谁能给我一小段，因为我没有在文档中找到任何示例？

更准确地说，我有包含 30 条线的终点和起点的矢量 vector<Vec4f> lines;，所以我想使用幅度来计算每条线的长度。我学会了如何通过 for 循环使用 norm 但我想使用 magnitude 所以我这样做了：

double x;
length=magnitude(lines[i][2]-lines[i][0],lines[i][3]-lines[i][1],x)

但它不起作用。我试图将 x 定义为 1 个数组向量，但我不能。

Answer 1

您已经了解了如何使用 norm 计算距离：

Point2f a = ...
Point2f b = ..
double length = norm(a - b); // NORM_L2, NORM_L1

您也可以一次处理所有点。您首先需要将坐标从矢量转换为矩阵形式，然后就是简单的数学运算：

#include <opencv2\opencv.hpp>
#include <iostream>
using namespace std;
using namespace cv;

int main() 
{
    vector<Vec4f> lines{ { 1, 2, 4, 6 }, { 5, 7, 1, 3 }, { 11, 12, 12, 11 } };

    Mat1f coordinates = Mat4f(lines).reshape(1);
    Mat1f diff_x = coordinates.col(0) - coordinates.col(2);
    Mat1f diff_y = coordinates.col(1) - coordinates.col(3);

    cout << "coordinates: \n" << coordinates << "\n\n";
    cout << "diff_x: \n" << diff_x << "\n\n";
    cout << "diff_y: \n" << diff_y << "\n\n";
    cout << endl;

    // sqrt((x2 - x1)^2 + (y2 - y1)^2)
    Mat1f euclidean_distance;
    magnitude(diff_x, diff_y, euclidean_distance);

    cout << "euclidean_distance: \n" << euclidean_distance << "\n\n";

    // abs(x2 - x1) + abs(y2 - y1)
    Mat1f manhattan_distance = abs(diff_x) + abs(diff_y);

    cout << "manhattan_distance: \n" << manhattan_distance << "\n\n";

    // Another way to compute L1 distance, with absdiff
    // abs(x2 - x1) + abs(y2 - y1)
    Mat1f points1 = coordinates(Range::all(), Range(0, 2));
    Mat1f points2 = coordinates(Range::all(), Range(2, 4));
    Mat1f other_manhattan_distance;
    absdiff(points1, points2, other_manhattan_distance);
    other_manhattan_distance = other_manhattan_distance.col(0) + other_manhattan_distance.col(1);

    cout << "other_manhattan_distance: \n" << other_manhattan_distance << "\n\n";

    return 0;
}

如何使用 magnitude 和 absdiff OpenCV 函数来计算距离？

How to use magnitude and absdiff OpenCV functions to compute distances?

opencv

opencv3.0