XplorePlane/XP.Calibration/Core/BallDetector.cs

using System.Drawing;
using Emgu.CV;
using Emgu.CV.CvEnum;
using Emgu.CV.Structure;
using Emgu.CV.Util;

namespace XP.Calibration.Core;

/// <summary>
/// 球心检测器 | Ball center detector from projection images
/// </summary>
public static class BallDetector
{
    /// <summary>
    /// 是否启用亚像素质心 | Enable sub-pixel centroid
    /// </summary>
    public static bool EnableSubPixel { get; set; } = true;

    /// <summary>
    /// 从单帧投影中检测球心 (自适应阈值 + 亚像素质心法)
    /// </summary>
    public static bool DetectCenter(Mat srcFloat, out PointF center)
    {
        center = new PointF(-1, -1);

        // 归一化到 0-255
        using var img8 = new Mat();
        CvInvoke.Normalize(srcFloat, img8, 0, 255, NormType.MinMax);
        img8.ConvertTo(img8, DepthType.Cv8U);
        CvInvoke.GaussianBlur(img8, img8, new Size(3, 3), 0.8);

        // 自适应阈值
        using var bin = new Mat();
        CvInvoke.AdaptiveThreshold(img8, bin, 255,
            AdaptiveThresholdType.MeanC, ThresholdType.Binary, 31, -5);

        // 查找轮廓
        using var contours = new VectorOfVectorOfPoint();
        CvInvoke.FindContours(bin, contours, null,
            RetrType.External, ChainApproxMethod.ChainApproxNone);

        if (contours.Size == 0)
            return false;

        // 找最大轮廓
        int maxIdx = 0;
        double maxArea = 0;
        for (int i = 0; i < contours.Size; i++)
        {
            double area = CvInvoke.ContourArea(contours[i]);
            if (area > maxArea)
            {
                maxArea = area;
                maxIdx = i;
            }
        }

        // 创建掩膜
        using var mask = new Mat(srcFloat.Size, DepthType.Cv8U, 1);
        mask.SetTo(new MCvScalar(0));
        CvInvoke.DrawContours(mask, contours, maxIdx, new MCvScalar(255), -1);

        if (EnableSubPixel)
        {
            center = SubPixelCentroid(srcFloat, mask);
        }
        else
        {
            var moments = CvInvoke.Moments(contours[maxIdx]);
            center = new PointF(
                (float)(moments.M10 / moments.M00),
                (float)(moments.M01 / moments.M00));
        }

        return center.X >= 0 && center.Y >= 0;
    }

    /// <summary>
    /// 从单帧投影中检测球心 (Canny 边缘 + 椭圆拟合法)
    /// </summary>
    public static bool DetectCenterByEllipse(Mat srcFloat, out PointF center)
    {
        center = new PointF(-1, -1);

        using var img8 = new Mat();
        CvInvoke.Normalize(srcFloat, img8, 0, 255, NormType.MinMax);
        img8.ConvertTo(img8, DepthType.Cv8U);
        CvInvoke.GaussianBlur(img8, img8, new Size(3, 3), 0.8);

        using var edges = new Mat();
        CvInvoke.Canny(img8, edges, 30, 80);

        using var contours = new VectorOfVectorOfPoint();
        CvInvoke.FindContours(edges, contours, null,
            RetrType.External, ChainApproxMethod.ChainApproxNone);

        if (contours.Size == 0)
            return false;

        int maxIdx = 0;
        double maxArea = 0;
        for (int i = 0; i < contours.Size; i++)
        {
            double area = CvInvoke.ContourArea(contours[i]);
            if (area > maxArea)
            {
                maxArea = area;
                maxIdx = i;
            }
        }

        if (contours[maxIdx].Size < 5)
            return false;

        using var points = new VectorOfPointF(
            Array.ConvertAll(contours[maxIdx].ToArray(), p => new PointF(p.X, p.Y)));
        var ellipse = CvInvoke.FitEllipse(points);
        center = ellipse.Center;

        return true;
    }

    /// <summary>
    /// 亚像素质心计算 | Sub-pixel centroid using intensity weighting
    /// </summary>
    private static PointF SubPixelCentroid(Mat imgFloat, Mat mask)
    {
        double sumI = 0, sumX = 0, sumY = 0;

        var imgData = imgFloat.GetData() as float[,];
        var maskData = mask.GetData() as byte[,];

        if (imgData == null || maskData == null)
            return new PointF(-1, -1);

        int rows = imgFloat.Rows;
        int cols = imgFloat.Cols;

        for (int y = 0; y < rows; y++)
        {
            for (int x = 0; x < cols; x++)
            {
                if (maskData[y, x] != 0)
                {
                    double intensity = imgData[y, x];
                    sumI += intensity;
                    sumX += x * intensity;
                    sumY += y * intensity;
                }
            }
        }

        if (sumI == 0)
            return new PointF(-1, -1);

        return new PointF((float)(sumX / sumI), (float)(sumY / sumI));
    }
}