harris_corners_detector.cpp

#include "harris_corners_detector.h"

harris_corners_detector::harris_corners_detector():neighbourhood(3), aperture(3),
k(0.01), maxStrength(0.0),
threshold(0.01), nonMaxSize(3)
{
}

void harris_corners_detector::detect(const cv::Mat& image) {
// Harris computation
    cv::cornerHarris(image,cornerStrength,
                     neighbourhood,// neighborhood size
                     aperture, // aperture size
                     k); // Harris parameter
    // internal threshold computation
    double minStrength; // not used
    cv::minMaxLoc(cornerStrength,
                  &minStrength,&maxStrength);
    // local maxima detection
    cv::Mat dilated; // temporary image
    cv::dilate(cornerStrength,dilated,cv::Mat());
    cv::compare(cornerStrength,dilated,
                localMax,cv::CMP_EQ);
}

cv::Mat harris_corners_detector::getCornerMap(double qualityLevel) {
    cv::Mat cornerMap;
    // thresholding the corner strength
    threshold= qualityLevel*maxStrength;
    cv::threshold(cornerStrength,cornerTh,
                  threshold,255,cv::THRESH_BINARY);
    // convert to 8-bit image
    cornerTh.convertTo(cornerMap,CV_8U);
    // non-maxima suppression
    cv::bitwise_and(cornerMap,localMax,cornerMap);
    return cornerMap;
}

void harris_corners_detector::getCorners(std::vector<cv::Point> &points,
double qualityLevel) {
    // Get the corner map
    cv::Mat cornerMap= getCornerMap(qualityLevel);
    // Get the corners
    getCorners(points, cornerMap);
}

void harris_corners_detector::getCorners(std::vector<cv::Point> &points,
const cv::Mat& cornerMap) {
    // Iterate over the pixels to obtain all features
    for( int y = 0; y < cornerMap.rows; y++ ) {
        const uchar* rowPtr = cornerMap.ptr<uchar>(y);
        for( int x = 0; x < cornerMap.cols; x++ ) {
            // if it is a feature point
            if (rowPtr[x]) {
                points.push_back(cv::Point(x,y));
            }
        }
    }
}

void harris_corners_detector::drawOnImage(cv::Mat &image,const std::vector<cv::Point> &points,cv::Scalar color,int radius, int thickness) {
    std::vector<cv::Point>::const_iterator it=
            points.begin();
    // for all corners
    while (it!=points.end()) {
        // draw a circle at each corner location
        cv::circle(image,*it,radius,color,thickness);
        ++it;
    }
}