IslandPerimeter.cpp

#include <opencv2/opencv.hpp>
#include <cstdio> 
#include <algorithm> 

using Contour = std::vector<cv::Point>;


void extractBlueRegion(
    const cv::Mat &src, cv::Mat &dst, uchar bLow, uchar bHigh)
{
    CV_Assert(!src.empty() && src.type() == CV_8UC3);
    CV_Assert(bLow <= bHigh);

    std::vector<cv::Mat> planes;
    cv::split(src, planes);
    cv::Mat &b = planes[0];

    cv::threshold(b, dst, bLow, 255, cv::THRESH_TOZERO);
    cv::threshold(dst, dst, bHigh, 255, cv::THRESH_TOZERO_INV);
    cv::threshold(dst, dst, 0, 255, cv::THRESH_BINARY);
}

double distance(cv::Point2d a, cv::Point2d b)
{
    return std::sqrt(std::pow(a.x - b.x, 2) + std::pow(a.y - b.y, 2));
}

cv::Point2d getCentroid(const Contour &contour)
{
    cv::Moments m = cv::moments(contour, false); 
    return cv::Point2d(m.m10 / m.m00, m.m01 / m.m00);
}

void orderContoursByDistanceToCenter(std::vector<Contour> &contours, const cv::Mat &image)
{
    cv::Point2d center(image.cols / 2.0, image.rows / 2.0);

    std::sort(contours.begin(), contours.end(), [center](const Contour &a, const Contour &b) -> int
    {
        double aDist = distance(center, getCentroid(a));
        double bDist = distance(center, getCentroid(b));
        return (aDist < bDist);
    });
}

double pixelToKilometer(double pixelLength, double z)
{
    // google mapsのz値(100倍)の値と、1ピクセルあたりのkm縮尺の対
    static std::unordered_map<int, double> lut;
    lut[775] = 50 / 97.0;  // 50kmで97px の縮尺だった
    lut[1075] = 5 / 80.0;  
    lut[1000] = 10 / 88.0;
    lut[1200] = 2 / 77.0;

    // zを100倍にし、25刻みにする (小数のキーを一応避ける)
    int zInteger = int(z);
    double zDecimal = z - zInteger;
    int key = (zInteger * 100) + (int((zDecimal + 0.125/*四捨五入的な*/) * 4) * 100 / 4);

    if (lut.find(key) != lut.end())
        return pixelLength * lut[key];

    return -1;
}

void drawSingleContour(const Contour &contour, const cv::Mat &src, cv::Mat &dst)
{
    src.copyTo(dst);
    std::vector<Contour> contours = { contour };
    cv::drawContours(dst, contours, -1, cv::Scalar(0, 0, 255), 2);
}

int main(int argc, char* argv[])
{
    if (argc < 2)
        return EXIT_FAILURE;
    const char *file = argv[1];

    cv::Mat src = cv::imread(file);
    
    // 海領域
    cv::Mat blueRegion;
    extractBlueRegion(src, blueRegion, 250,255);

    // 陸に置き換える
    cv::Mat land;
    cv::bitwise_not(blueRegion, land);

    // 輪郭
    std::vector<Contour> contours;
    cv::findContours(land, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);

    //cv::Mat view = src.clone();
    //cv::drawContours(view, contours, -1, cv::Scalar(0, 0, 255), 3);

    orderContoursByDistanceToCenter(contours, src);
    const Contour &islandContour = contours[0];

    double perimeter = cv::arcLength(islandContour, true);
    //double kilometer = pixelToKilometer(perimeter, 10.75);
    //double kilometer = pixelToKilometer(perimeter, 7.75);
    double kilometer = pixelToKilometer(perimeter, 12.00);
    if (kilometer < 0)
    {
        std::puts("pixelToKilometer失敗(z値未登録？)");
        return EXIT_FAILURE;
    }
    std::printf("周囲長: %.2fkm\n", kilometer);

    cv::Mat view;
    drawSingleContour(islandContour, src, view);

    cv::imshow("blueRegion", blueRegion);
    cv::imshow("view", view);
    cv::waitKey();
    cv::destroyAllWindows();

    return 0;
}