c++ - 二维点数据集中的 OpenCV 模板

Question

我在想什么是检测二维点数组中“图形”的最佳方法。

在这个例子中，我有两个"template"。图1是模板，图2是模板。这些模板中的每一个都仅作为具有 x,y 坐标的点的 vector 存在。

假设我们有第三个 vector ，其中的点具有 x,y 坐标

在第三个数组中找出并隔离与前两个数组之一匹配的点的最佳方法是什么。 (包括缩放、旋转)？

我一直在尝试最近的邻居(FlannBasedMatcehr)甚至 SVM 实现，但它似乎没有给我任何结果，我认为模板匹配似乎也不是可行的方法。我不是在处理图像，而是在内存中处理二维点...

特别是因为输入 vector 总是比要与之比较的原始数据集有更多的点。

它需要做的就是在数组中找到与模板匹配的点。

我不是机器学习或 opencv 方面的“专家”。我想我从一开始就忽略了一些东西......

非常感谢您的帮助/建议。

Answer 1

只是为了好玩我试过这个:

1. 选择点数据集中的两个点并计算将前两个模式点映射到这些点的转换。
2. 测试是否可以在数据集中找到所有转换后的模式点。

这种方法非常幼稚，复杂度为 O(m*n²)，有 n 个数据点和大小为 m(点)的单一模式。对于某些最近邻搜索方法，这种复杂性可能会增加。所以你必须考虑它是否对你的应用程序来说不够高效。

一些改进可能包括一些启发式方法，以不选择所有 n² 点组合，但是，您需要最大模式缩放或类似信息的背景信息。

为了评估，我首先创建了一个模式:

然后我创建随机点并在其中某处添加图案(缩放、旋转和平移):

经过一些计算，此方法可以识别模式。红线表示选择的转换计算点。

代码如下:

// draw a set of points on a given destination image
void drawPoints(cv::Mat & image, std::vector<cv::Point2f> points, cv::Scalar color = cv::Scalar(255,255,255), float size=10)
{
    for(unsigned int i=0; i<points.size(); ++i)
    {
        cv::circle(image, points[i], 0, color, size);
    }
}

// assumes a 2x3 (affine) transformation (CV_32FC1). does not change the input points
std::vector<cv::Point2f> applyTransformation(std::vector<cv::Point2f> points, cv::Mat transformation)
{
    for(unsigned int i=0; i<points.size(); ++i)
    {
        const cv::Point2f tmp = points[i];
        points[i].x = tmp.x * transformation.at<float>(0,0) + tmp.y * transformation.at<float>(0,1) + transformation.at<float>(0,2) ;
        points[i].y = tmp.x * transformation.at<float>(1,0) + tmp.y * transformation.at<float>(1,1) + transformation.at<float>(1,2) ;
    }

    return points;
}

const float PI = 3.14159265359;

// similarity transformation uses same scaling along both axes, rotation and a translation part
cv::Mat composeSimilarityTransformation(float s, float r, float tx, float ty)
{
    cv::Mat transformation = cv::Mat::zeros(2,3,CV_32FC1);

    // compute rotation matrix and scale entries
    float rRad = PI*r/180.0f;
    transformation.at<float>(0,0) = s*cosf(rRad);
    transformation.at<float>(0,1) = s*sinf(rRad);
    transformation.at<float>(1,0) = -s*sinf(rRad);
    transformation.at<float>(1,1) = s*cosf(rRad);

    // translation
    transformation.at<float>(0,2) = tx;
    transformation.at<float>(1,2) = ty;

    return transformation;

}

// create random points
std::vector<cv::Point2f> createPointSet(cv::Size2i imageSize, std::vector<cv::Point2f> pointPattern, unsigned int nRandomDots = 50)
{
    // subtract center of gravity to allow more intuitive rotation
    cv::Point2f centerOfGravity(0,0);
    for(unsigned int i=0; i<pointPattern.size(); ++i)
    {
        centerOfGravity.x += pointPattern[i].x;
        centerOfGravity.y += pointPattern[i].y;
    }
    centerOfGravity.x /= (float)pointPattern.size();
    centerOfGravity.y /= (float)pointPattern.size();
    pointPattern = applyTransformation(pointPattern, composeSimilarityTransformation(1,0,-centerOfGravity.x, -centerOfGravity.y));

    // create random points
    //unsigned int nRandomDots = 0;
    std::vector<cv::Point2f> pointset;
    srand (time(NULL));
    for(unsigned int i =0; i<nRandomDots; ++i)
    {
        pointset.push_back( cv::Point2f(rand()%imageSize.width, rand()%imageSize.height) );
    }

    cv::Mat image = cv::Mat::ones(imageSize,CV_8UC3);
    image = cv::Scalar(255,255,255);

    drawPoints(image, pointset, cv::Scalar(0,0,0));
    cv::namedWindow("pointset"); cv::imshow("pointset", image);

    // add point pattern to a random location

    float scaleFactor = rand()%30 + 10.0f;
    float translationX = rand()%(imageSize.width/2)+ imageSize.width/4;
    float translationY = rand()%(imageSize.height/2)+ imageSize.height/4;
    float rotationAngle = rand()%360;

    std::cout << "s: " << scaleFactor << " r: " << rotationAngle << " t: " << translationX << "/" << translationY << std::endl;


    std::vector<cv::Point2f> transformedPattern = applyTransformation(pointPattern,composeSimilarityTransformation(scaleFactor,rotationAngle,translationX,translationY));
    //std::vector<cv::Point2f> transformedPattern = applyTransformation(pointPattern,trans);

    drawPoints(image, transformedPattern, cv::Scalar(0,0,0));
    drawPoints(image, transformedPattern, cv::Scalar(0,255,0),3);
    cv::imwrite("dataPoints.png", image);
    cv::namedWindow("pointset + pattern"); cv::imshow("pointset + pattern", image);



    for(unsigned int i=0; i<transformedPattern.size(); ++i)
        pointset.push_back(transformedPattern[i]);

    return pointset;

}

void programDetectPointPattern()
{
    cv::Size2i imageSize(640,480);

    // create a point pattern, this can be in any scale and any relative location
    std::vector<cv::Point2f> pointPattern;
    pointPattern.push_back(cv::Point2f(0,0));
    pointPattern.push_back(cv::Point2f(2,0));
    pointPattern.push_back(cv::Point2f(4,0));
    pointPattern.push_back(cv::Point2f(1,2));
    pointPattern.push_back(cv::Point2f(3,2));
    pointPattern.push_back(cv::Point2f(2,4));

    // transform the pattern so it can be drawn
    cv::Mat trans = cv::Mat::ones(2,3,CV_32FC1);
    trans.at<float>(0,0) = 20.0f;   // scale x
    trans.at<float>(1,1) = 20.0f;   // scale y
    trans.at<float>(0,2) = 20.0f;   // translation x
    trans.at<float>(1,2) = 20.0f;   // translation y

    // draw the pattern
    cv::Mat drawnPattern = cv::Mat::ones(cv::Size2i(128,128),CV_8U);
    drawnPattern *= 255;
    drawPoints(drawnPattern,applyTransformation(pointPattern, trans), cv::Scalar(0),5);

    // display and save pattern
    cv::imwrite("patternToDetect.png", drawnPattern);
    cv::namedWindow("pattern"); cv::imshow("pattern", drawnPattern);

    // draw the points and the included pattern
    std::vector<cv::Point2f> pointset = createPointSet(imageSize, pointPattern);
    cv::Mat image = cv::Mat(imageSize, CV_8UC3);
    image = cv::Scalar(255,255,255);
    drawPoints(image,pointset, cv::Scalar(0,0,0));


    // normally we would have to use some nearest neighbor distance computation, but to make it easier here,
    // we create a small area around every point, which allows to test for point existence in a small neighborhood very efficiently (for small images)
    // in the real application this "inlier" check should be performed by k-nearest neighbor search and threshold the distance,
    // efficiently evaluated by a kd-tree
    cv::Mat pointImage = cv::Mat::zeros(imageSize,CV_8U);
    float maxDist = 3.0f; // how exact must the pattern be recognized, can there be some "noise" in the position of the data points?
    drawPoints(pointImage, pointset, cv::Scalar(255),maxDist);
    cv::namedWindow("pointImage"); cv::imshow("pointImage", pointImage);

    // choose two points from the pattern (can be arbitrary so just take the first two)
    cv::Point2f referencePoint1 = pointPattern[0];
    cv::Point2f referencePoint2 = pointPattern[1];
    cv::Point2f diff1;  // difference vector
    diff1.x = referencePoint2.x - referencePoint1.x;
    diff1.y = referencePoint2.y - referencePoint1.y;
    float referenceLength = sqrt(diff1.x*diff1.x + diff1.y*diff1.y);
    diff1.x = diff1.x/referenceLength; diff1.y = diff1.y/referenceLength;

    std::cout << "reference: " << std::endl;
    std::cout << referencePoint1 << std::endl;

    // now try to find the pattern
    for(unsigned int j=0; j<pointset.size(); ++j)
    {
        cv::Point2f targetPoint1 =  pointset[j];

        for(unsigned int i=0; i<pointset.size(); ++i)
        {
            cv::Point2f targetPoint2 =  pointset[i];

            cv::Point2f diff2;
            diff2.x = targetPoint2.x - targetPoint1.x;
            diff2.y = targetPoint2.y - targetPoint1.y;
            float targetLength = sqrt(diff2.x*diff2.x + diff2.y*diff2.y);
            diff2.x = diff2.x/targetLength; diff2.y = diff2.y/targetLength;

            // with nearest-neighborhood search this line will be similar or the maximal neighbor distance must be relative to targetLength!
            if(targetLength < maxDist) continue;

            // scale:
            float s = targetLength/referenceLength;

            // rotation:
            float r = -180.0f/PI*(atan2(diff2.y,diff2.x) + atan2(diff1.y,diff1.x));

            // scale and rotate the reference point to compute the translation needed
            std::vector<cv::Point2f> origin;
            origin.push_back(referencePoint1);
            origin = applyTransformation(origin, composeSimilarityTransformation(s,r,0,0));
            // compute the translation which maps the two reference points on the two target points
            float tx = targetPoint1.x - origin[0].x;
            float ty = targetPoint1.y - origin[0].y;

            std::vector<cv::Point2f> transformedPattern = applyTransformation(pointPattern,composeSimilarityTransformation(s,r,tx,ty));


            // now test if all transformed pattern points can be found in the dataset
            bool found = true;
            for(unsigned int i=0; i<transformedPattern.size(); ++i)
            {
                cv::Point2f curr = transformedPattern[i];
                // here we check whether there is a point drawn in the image. If you have no image you will have to perform a nearest neighbor search.
                // this can be done with a balanced kd-tree in O(log n) time
                // building such a balanced kd-tree has to be done once for the whole dataset and needs O(n*(log n)) afair
                if((curr.x >= 0)&&(curr.x <= pointImage.cols-1)&&(curr.y>=0)&&(curr.y <= pointImage.rows-1))
                {
                    if(pointImage.at<unsigned char>(curr.y, curr.x) == 0) found = false;
                    // if working with kd-tree: if nearest neighbor distance > maxDist => found = false;
                }
                else found = false;

            }



            if(found)
            {
                std::cout << composeSimilarityTransformation(s,r,tx,ty) << std::endl;
                cv::Mat currentIteration;
                image.copyTo(currentIteration);
                cv::circle(currentIteration,targetPoint1,5, cv::Scalar(255,0,0),1);
                cv::circle(currentIteration,targetPoint2,5, cv::Scalar(255,0,255),1);
                cv::line(currentIteration,targetPoint1,targetPoint2,cv::Scalar(0,0,255));
                drawPoints(currentIteration, transformedPattern, cv::Scalar(0,0,255),4);

                cv::imwrite("detectedPattern.png", currentIteration);
                cv::namedWindow("iteration"); cv::imshow("iteration", currentIteration); cv::waitKey(-1);
            }

        }
    }


}