loam源码解析： scanRegistration（二）

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scanRegistration.cpp解析二

六、点云回调函数laserCloudHandler
- 1 遍历点云中每一个点，进行校正
- - 1.1 如果收到IMU数据,使用IMU矫正点云畸变：
  - 1.2 将每个点放入对应线号的容器
- 2 去除不靠点，提取特征点
- - 2.1 计算各个点云点的曲率
  - 2.2 筛选特征点
  - 2.3 提取特征点
- 3 发布ROS消息

LOAM: Lidar Odometry and Mapping in Real-time 论文阅读: https://blog.csdn.net/weixin_44156680/article/details/117876839.
loam源码： https://github.com/cuitaixiang/LOAM_NOTED.

六、点云回调函数laserCloudHandler

继续讨论，该函数主要是实现接收并处理点云数据，其中velodyne雷达坐标系安装为x轴向前，y轴向左，z轴向上的右手坐标系。

丢弃前20个点云数据:

if (!systemInited) {
    systemInitCount++;
    if (systemInitCount >= systemDelay) {
      systemInited = true;
    }
    return;
  }

记录每个scan有曲率的点的开始和结束索引:

  std::vector<int> scanStartInd(N_SCANS, 0);
  std::vector<int> scanEndInd(N_SCANS, 0);

获取当前点云时间(在ROS中获取时间戳一般为:MsgPtr->header.stamp.toSec() )：

  double timeScanCur = laserCloudMsg->header.stamp.toSec();

ROS中点云信息的储存一般有两种方式sensor_msgs::PointCloud2ConstPtr、sensor_msgs::PointCloudConstPtr，其中还包含有除了点坐标信息之外的其他信息（比如时间），在ROS中提供这两者的转换函数sensor_msgs::convertPointCloud2ToPointCloud和sensor_msgs::convertPointCloudToPointCloud2，而在pcl库中的点云储存是pcl::PointCloud<PointType>，PointType一般也有两种方式pcl::PointXYZI以及pcl::PointXYZ（区别在于有没有intensity信息）。同时在pcl库也提供PointCloud2和pcl::PointCloud之间的转换使用pcl::fromROSMsg和pcl::toROSMsg。

  pcl::PointCloud<pcl::PointXYZ> laserCloudIn;
  //消息转换成pcl数据存放
  pcl::fromROSMsg(*laserCloudMsg, laserCloudIn);
  std::vector<int> indices;

pcl::removeNaNFromPointCloud(laserCloudIn, laserCloudIn, indices);函数有三个参数，分别为输入点云，输出点云及对应保留的索引。

//移除空点
pcl::removeNaNFromPointCloud(laserCloudIn, laserCloudIn, indices);

任何一个scan的激光点数据并不是都是从y轴正向开始的2π区域，而是与正向夹角有一定的误差：

//点云点的数量
int cloudSize = laserCloudIn.points.size();
//lidar scan开始点的旋转角,atan2范围[-pi,+pi],计算旋转角时取负号是因为velodyne是顺时针旋转
float startOri = -atan2(laserCloudIn.points[0].y, laserCloudIn.points[0].x);
//lidar scan结束点的旋转角，加2*pi使点云旋转周期为2*pi
float endOri = -atan2(laserCloudIn.points[cloudSize - 1].y,
                      laserCloudIn.points[cloudSize - 1].x) + 2 * M_PI;

结束方位角与开始方位角差值控制在(PI,3*PI)范围，允许lidar不是一个圆周扫描，正常情况下在这个范围内：π< endOri - startOri < 3π，异常则修正：

  if (endOri - startOri > 3 * M_PI) {
    endOri -= 2 * M_PI;
  } else if (endOri - startOri < M_PI) {
    endOri += 2 * M_PI;
  }

1 遍历点云中每一个点，进行校正

  //lidar扫描线是否旋转过半
  bool halfPassed = false;
  int count = cloudSize;
  PointType point;
  std::vector<pcl::PointCloud<PointType> > laserCloudScans(N_SCANS);
  for (int i = 0; i < cloudSize; i++) {
  	.......//如下拆解分析

交换坐标轴，与论文保持一致：

    //坐标轴交换，velodyne lidar的坐标系也转换到z轴向前，x轴向左的右手坐标系
    point.x = laserCloudIn.points[i].y;
    point.y = laserCloudIn.points[i].z;
    point.z = laserCloudIn.points[i].x;

确定每个激光点的线束：

    //计算点的仰角(根据lidar文档垂直角计算公式),根据仰角排列激光线号，velodyne每两个scan之间间隔2度
    float angle = atan(point.y / sqrt(point.x * point.x + point.z * point.z)) * 180 / M_PI;
    int scanID;
    //仰角四舍五入(加减0.5截断效果等于四舍五入)
    int roundedAngle = int(angle + (angle<0.0?-0.5:+0.5)); 
    if (roundedAngle > 0){
      scanID = roundedAngle;
    }
    else {
      scanID = roundedAngle + (N_SCANS - 1);
    }
    //过滤点，只挑选[-15度，+15度]范围内的点,scanID属于[0,15]
    if (scanID > (N_SCANS - 1) || scanID < 0 ){
      count--;
      continue;
    }

这里目前还不是很理解，为什么要判断是否转过半圈：

    //该点的旋转角
    float ori = -atan2(point.x, point.z);
    if (!halfPassed) {//根据扫描线是否旋转过半选择与起始位置还是终止位置进行差值计算，从而进行补偿
        //确保-pi/2 < ori - startOri < 3*pi/2
      if (ori < startOri - M_PI / 2) {
        ori += 2 * M_PI;
      } else if (ori > startOri + M_PI * 3 / 2) {
        ori -= 2 * M_PI;
      }

      if (ori - startOri > M_PI) {
        halfPassed = true;
      }
    } else {
      ori += 2 * M_PI;

      //确保-3*pi/2 < ori - endOri < pi/2
      if (ori < endOri - M_PI * 3 / 2) {
        ori += 2 * M_PI;
      } else if (ori > endOri + M_PI / 2) {
        ori -= 2 * M_PI;
      } 
    }

确定相对时间和点强度：

    //-0.5 < relTime < 1.5（点旋转的角度与整个周期旋转角度的比率, 即点云中点的相对时间）
    float relTime = (ori - startOri) / (endOri - startOri);
    //点强度=线号+点相对时间（即一个整数+一个小数，整数部分是线号，小数部分是该点的相对时间）,匀速扫描：根据当前扫描的角度和扫描周期计算相对扫描起始位置的时间
    point.intensity = scanID + scanPeriod * relTime;

1.1 如果收到IMU数据,使用IMU矫正点云畸变：

if (imuPointerLast >= 0) {
	......//分析如下拆解

寻找imu时间超出lidar时间的位置：

    //点时间=点云时间+周期时间
      float pointTime = relTime * scanPeriod;//计算点的周期时间
      //寻找是否有点云的时间戳小于IMU的时间戳的IMU位置:imuPointerFront
      while (imuPointerFront != imuPointerLast) {
        if (timeScanCur + pointTime < imuTime[imuPointerFront]) {
          break;
        }
        imuPointerFront = (imuPointerFront + 1) % imuQueLength;
      }

要是没找到imu超前lidar的时间戳，此时imuPointerFront==imtPointerLast,只能以当前收到的最新的IMU的速度，位移，欧拉角作为当前点的速度，位移，欧拉角使用：

   if (timeScanCur + pointTime > imuTime[imuPointerFront]) {//没找到,
        imuRollCur = imuRoll[imuPointerFront];
        imuPitchCur = imuPitch[imuPointerFront];
        imuYawCur = imuYaw[imuPointerFront];

        imuVeloXCur = imuVeloX[imuPointerFront];
        imuVeloYCur = imuVeloY[imuPointerFront];
        imuVeloZCur = imuVeloZ[imuPointerFront];

        imuShiftXCur = imuShiftX[imuPointerFront];
        imuShiftYCur = imuShiftY[imuPointerFront];
        imuShiftZCur = imuShiftZ[imuPointerFront];
      }

要是找到imu超前lidar的时间戳，对当前的运动信息进行线形插值：

else {//找到了点云时间戳小于IMU时间戳的IMU位置,则该点必处于imuPointerBack和imuPointerFront之间，据此线性插值，计算点云点的速度，位移和欧拉角
        int imuPointerBack = (imuPointerFront + imuQueLength - 1) % imuQueLength;
        //按时间距离计算权重分配比率,也即线性插值
        float ratioFront = (timeScanCur + pointTime - imuTime[imuPointerBack]) 
                         / (imuTime[imuPointerFront] - imuTime[imuPointerBack]);
        float ratioBack = (imuTime[imuPointerFront] - timeScanCur - pointTime) 
                        / (imuTime[imuPointerFront] - imuTime[imuPointerBack]);

        imuRollCur = imuRoll[imuPointerFront] * ratioFront + imuRoll[imuPointerBack] * ratioBack;
        imuPitchCur = imuPitch[imuPointerFront] * ratioFront + imuPitch[imuPointerBack] * ratioBack;
        if (imuYaw[imuPointerFront] - imuYaw[imuPointerBack] > M_PI) {
          imuYawCur = imuYaw[imuPointerFront] * ratioFront + (imuYaw[imuPointerBack] + 2 * M_PI) * ratioBack;
        } else if (imuYaw[imuPointerFront] - imuYaw[imuPointerBack] < -M_PI) {
          imuYawCur = imuYaw[imuPointerFront] * ratioFront + (imuYaw[imuPointerBack] - 2 * M_PI) * ratioBack;
        } else {
          imuYawCur = imuYaw[imuPointerFront] * ratioFront + imuYaw[imuPointerBack] * ratioBack;
        }

        //本质:imuVeloXCur = imuVeloX[imuPointerback] + (imuVelX[imuPointerFront]-imuVelX[imuPoniterBack])*ratioFront
        imuVeloXCur = imuVeloX[imuPointerFront] * ratioFront + imuVeloX[imuPointerBack] * ratioBack;
        imuVeloYCur = imuVeloY[imuPointerFront] * ratioFront + imuVeloY[imuPointerBack] * ratioBack;
        imuVeloZCur = imuVeloZ[imuPointerFront] * ratioFront + imuVeloZ[imuPointerBack] * ratioBack;

        imuShiftXCur = imuShiftX[imuPointerFront] * ratioFront + imuShiftX[imuPointerBack] * ratioBack;
        imuShiftYCur = imuShiftY[imuPointerFront] * ratioFront + imuShiftY[imuPointerBack] * ratioBack;
        imuShiftZCur = imuShiftZ[imuPointerFront] * ratioFront + imuShiftZ[imuPointerBack] * ratioBack;
      }

如果是第一个点,记住点云起始位置的速度，位移，欧拉角：

      if (i == 0) {
        imuRollStart = imuRollCur;
        imuPitchStart = imuPitchCur;
        imuYawStart = imuYawCur;

        imuVeloXStart = imuVeloXCur;
        imuVeloYStart = imuVeloYCur;
        imuVeloZStart = imuVeloZCur;

        imuShiftXStart = imuShiftXCur;
        imuShiftYStart = imuShiftYCur;
        imuShiftZStart = imuShiftZCur;
      }

计算之后每个点相对于第一个点的由于加减速非匀速运动产生的位移速度畸变，并对点云中的每个点位置信息重新补偿矫正（以下函数另行分析）：

else {
        ShiftToStartIMU(pointTime);
        VeloToStartIMU();
        TransformToStartIMU(&point);
      }
    }

1.2 将每个点放入对应线号的容器

 laserCloudScans[scanID].push_back(point);

2 去除不靠点，提取特征点

将各束激光线的点云信息通过ID大小拼接成一个点云：

  cloudSize = count;
  pcl::PointCloud<PointType>::Ptr laserCloud(new pcl::PointCloud<PointType>());
  for (int i = 0; i < N_SCANS; i++) {//将所有的点按照线号从小到大放入一个容器
    *laserCloud += laserCloudScans[i];
  }

2.1 计算各个点云点的曲率

  //获得有效范围内的点的数量
  int scanCount = -1;
  for (int i = 5; i < cloudSize - 5; i++) {//使用每个点的前后五个点计算曲率，因此前五个与最后五个点跳过
    float diffX = laserCloud->points[i - 5].x + laserCloud->points[i - 4].x 
                + laserCloud->points[i - 3].x + laserCloud->points[i - 2].x 
                + laserCloud->points[i - 1].x - 10 * laserCloud->points[i].x 
                + laserCloud->points[i + 1].x + laserCloud->points[i + 2].x
                + laserCloud->points[i + 3].x + laserCloud->points[i + 4].x
                + laserCloud->points[i + 5].x;
    float diffY = laserCloud->points[i - 5].y + laserCloud->points[i - 4].y 
                + laserCloud->points[i - 3].y + laserCloud->points[i - 2].y 
                + laserCloud->points[i - 1].y - 10 * laserCloud->points[i].y 
                + laserCloud->points[i + 1].y + laserCloud->points[i + 2].y
                + laserCloud->points[i + 3].y + laserCloud->points[i + 4].y
                + laserCloud->points[i + 5].y;
    float diffZ = laserCloud->points[i - 5].z + laserCloud->points[i - 4].z 
                + laserCloud->points[i - 3].z + laserCloud->points[i - 2].z 
                + laserCloud->points[i - 1].z - 10 * laserCloud->points[i].z 
                + laserCloud->points[i + 1].z + laserCloud->points[i + 2].z
                + laserCloud->points[i + 3].z + laserCloud->points[i + 4].z
                + laserCloud->points[i + 5].z;
    //曲率计算
    cloudCurvature[i] = diffX * diffX + diffY * diffY + diffZ * diffZ;
    //记录曲率点的索引
    cloudSortInd[i] = i;
    //初始时，点全未筛选过
    cloudNeighborPicked[i] = 0;
    //初始化为less flat点
    cloudLabel[i] = 0;

    //每个scan，只有第一个符合的点会进来，因为每个scan的点都在一起存放
    if (int(laserCloud->points[i].intensity) != scanCount) {
      scanCount = int(laserCloud->points[i].intensity);//控制每个scan只进入第一个点

      //曲率只取同一个scan计算出来的，跨scan计算的曲率非法，排除，也即排除每个scan的前后五个点
      if (scanCount > 0 && scanCount < N_SCANS) {
        scanStartInd[scanCount] = i + 5;
        scanEndInd[scanCount - 1] = i - 5;
      }
    }
  }

2.2 筛选特征点

  //挑选点，排除容易被斜面挡住的点以及离群点，有些点容易被斜面挡住，而离群点可能出现带有偶然性，这些情况都可能导致前后两次扫描不能被同时看到
  for (int i = 5; i < cloudSize - 6; i++) {//与后一个点差值，所以减6
    float diffX = laserCloud->points[i + 1].x - laserCloud->points[i].x;
    float diffY = laserCloud->points[i + 1].y - laserCloud->points[i].y;
    float diffZ = laserCloud->points[i + 1].z - laserCloud->points[i].z;
    //计算有效曲率点与后一个点之间的距离平方和
    float diff = diffX * diffX + diffY * diffY + diffZ * diffZ;

若当前点与后一个点的距离过大（大于0.1），则需要判断两个激光点与雷达形成的角度大小，采取的办法是将远处的激光点拉回到近处（即将三点形成等腰三角形），在小角度的前提下，夹角近似为边长之比，若夹角较小，说明激光点所在平面与激光线近似平行，舍弃远处的激光点。

    if (diff > 0.1) {//前提:两个点之间距离要大于0.1

        //点的深度
      float depth1 = sqrt(laserCloud->points[i].x * laserCloud->points[i].x + 
                     laserCloud->points[i].y * laserCloud->points[i].y +
                     laserCloud->points[i].z * laserCloud->points[i].z);

      //后一个点的深度
      float depth2 = sqrt(laserCloud->points[i + 1].x * laserCloud->points[i + 1].x + 
                     laserCloud->points[i + 1].y * laserCloud->points[i + 1].y +
                     laserCloud->points[i + 1].z * laserCloud->points[i + 1].z);

      //按照两点的深度的比例，将深度较大的点拉回后计算距离
      if (depth1 > depth2) {
        diffX = laserCloud->points[i + 1].x - laserCloud->points[i].x * depth2 / depth1;
        diffY = laserCloud->points[i + 1].y - laserCloud->points[i].y * depth2 / depth1;
        diffZ = laserCloud->points[i + 1].z - laserCloud->points[i].z * depth2 / depth1;

        //边长比也即是弧度值，若小于0.1，说明夹角比较小，斜面比较陡峭,点深度变化比较剧烈,点处在近似与激光束平行的斜面上
        if (sqrt(diffX * diffX + diffY * diffY + diffZ * diffZ) / depth2 < 0.1) {//排除容易被斜面挡住的点
            //该点及前面五个点（大致都在斜面上）全部置为筛选过
          cloudNeighborPicked[i - 5] = 1;
          cloudNeighborPicked[i - 4] = 1;
          cloudNeighborPicked[i - 3] = 1;
          cloudNeighborPicked[i - 2] = 1;
          cloudNeighborPicked[i - 1] = 1;
          cloudNeighborPicked[i] = 1;
        }
      } else {
        diffX = laserCloud->points[i + 1].x * depth1 / depth2 - laserCloud->points[i].x;
        diffY = laserCloud->points[i + 1].y * depth1 / depth2 - laserCloud->points[i].y;
        diffZ = laserCloud->points[i + 1].z * depth1 / depth2 - laserCloud->points[i].z;

        if (sqrt(diffX * diffX + diffY * diffY + diffZ * diffZ) / depth1 < 0.1) {
          cloudNeighborPicked[i + 1] = 1;
          cloudNeighborPicked[i + 2] = 1;
          cloudNeighborPicked[i + 3] = 1;
          cloudNeighborPicked[i + 4] = 1;
          cloudNeighborPicked[i + 5] = 1;
          cloudNeighborPicked[i + 6] = 1;
        }
      }
    }

若当前点与前后两个点的距离都超过当前深度的0.0002，则视为离群点，舍弃。

    float diffX2 = laserCloud->points[i].x - laserCloud->points[i - 1].x;
    float diffY2 = laserCloud->points[i].y - laserCloud->points[i - 1].y;
    float diffZ2 = laserCloud->points[i].z - laserCloud->points[i - 1].z;
    //与前一个点的距离平方和
    float diff2 = diffX2 * diffX2 + diffY2 * diffY2 + diffZ2 * diffZ2;

    //点深度的平方和
    float dis = laserCloud->points[i].x * laserCloud->points[i].x
              + laserCloud->points[i].y * laserCloud->points[i].y
              + laserCloud->points[i].z * laserCloud->points[i].z;

    //与前后点的平方和都大于深度平方和的万分之二，这些点视为离群点，包括陡斜面上的点，强烈凸凹点和空旷区域中的某些点，置为筛选过，弃用
    if (diff > 0.0002 * dis && diff2 > 0.0002 * dis) {
      cloudNeighborPicked[i] = 1;
    }
  }

2.3 提取特征点

将所有点云分为四类：

  pcl::PointCloud<PointType> cornerPointsSharp;
  pcl::PointCloud<PointType> cornerPointsLessSharp;
  pcl::PointCloud<PointType> surfPointsFlat;
  pcl::PointCloud<PointType> surfPointsLessFlat;

将每个scan的曲率点分成6等份处理：

  //将每条线上的点分入相应的类别：边沿点和平面点
  for (int i = 0; i < N_SCANS; i++) {
    pcl::PointCloud<PointType>::Ptr surfPointsLessFlatScan(new pcl::PointCloud<PointType>);
    //将每个scan的曲率点分成6等份处理,确保周围都有点被选作特征点
    for (int j = 0; j < 6; j++) {
        //六等份起点：sp = scanStartInd + (scanEndInd - scanStartInd)*j/6
      int sp = (scanStartInd[i] * (6 - j)  + scanEndInd[i] * j) / 6;
      //六等份终点：ep = scanStartInd - 1 + (scanEndInd - scanStartInd)*(j+1)/6
      int ep = (scanStartInd[i] * (5 - j)  + scanEndInd[i] * (j + 1)) / 6 - 1;

      //按曲率从小到大冒泡排序
      for (int k = sp + 1; k <= ep; k++) {
        for (int l = k; l >= sp + 1; l--) {
            //如果后面曲率点大于前面，则交换
          if (cloudCurvature[cloudSortInd[l]] < cloudCurvature[cloudSortInd[l - 1]]) {
            int temp = cloudSortInd[l - 1];
            cloudSortInd[l - 1] = cloudSortInd[l];
            cloudSortInd[l] = temp;
          }
        }
      }

选取20个曲率比较大的点，以及两个曲率很大的点，选取以后舍弃特征点周围很近的点：

      //挑选每个分段的曲率很大和比较大的点
      int largestPickedNum = 0;
      for (int k = ep; k >= sp; k--) {
        int ind = cloudSortInd[k];  //曲率最大点的点序

        //如果曲率大的点，曲率的确比较大，并且未被筛选过滤掉
        if (cloudNeighborPicked[ind] == 0 &&
            cloudCurvature[ind] > 0.1) {
        
          largestPickedNum++;
          if (largestPickedNum <= 2) {//挑选曲率最大的前2个点放入sharp点集合
            cloudLabel[ind] = 2;//2代表点曲率很大
            cornerPointsSharp.push_back(laserCloud->points[ind]);
            cornerPointsLessSharp.push_back(laserCloud->points[ind]);
          } else if (largestPickedNum <= 20) {//挑选曲率最大的前20个点放入less sharp点集合
            cloudLabel[ind] = 1;//1代表点曲率比较尖锐
            cornerPointsLessSharp.push_back(laserCloud->points[ind]);
          } else {
            break;
          }

          cloudNeighborPicked[ind] = 1;//筛选标志置位

          //将曲率比较大的点的前后各5个连续距离比较近的点筛选出去，防止特征点聚集，使得特征点在每个方向上尽量分布均匀
          for (int l = 1; l <= 5; l++) {
            float diffX = laserCloud->points[ind + l].x 
                        - laserCloud->points[ind + l - 1].x;
            float diffY = laserCloud->points[ind + l].y 
                        - laserCloud->points[ind + l - 1].y;
            float diffZ = laserCloud->points[ind + l].z 
                        - laserCloud->points[ind + l - 1].z;
            if (diffX * diffX + diffY * diffY + diffZ * diffZ > 0.05) {
              break;
            }

            cloudNeighborPicked[ind + l] = 1;
          }
          for (int l = -1; l >= -5; l--) {
            float diffX = laserCloud->points[ind + l].x 
                        - laserCloud->points[ind + l + 1].x;
            float diffY = laserCloud->points[ind + l].y 
                        - laserCloud->points[ind + l + 1].y;
            float diffZ = laserCloud->points[ind + l].z 
                        - laserCloud->points[ind + l + 1].z;
            if (diffX * diffX + diffY * diffY + diffZ * diffZ > 0.05) {
              break;
            }

            cloudNeighborPicked[ind + l] = 1;
          }
        }
      }

选取4两个曲率很小的点，将剩余点作为曲率比较小的点，由于less flat点最多，对每个分段less flat的点进行体素栅格滤波，PCL实现的VoxelGrid类通过输入的点云数据创建一个三维体素栅格（可把体素栅格想象为微小的空间三维立方体的集合），然后setInputCloud输入点云，setLeafSize设置体素大小，在每个体素（即三维立方体）内，用体素中所有点的重心来近似显示体素中其他点，这样该体素就内所有点就用一个重心点最终表示，即filter的实现：

      //挑选每个分段的曲率很小比较小的点
      int smallestPickedNum = 0;
      for (int k = sp; k <= ep; k++) {
        int ind = cloudSortInd[k];

        //如果曲率的确比较小，并且未被筛选出
        if (cloudNeighborPicked[ind] == 0 &&
            cloudCurvature[ind] < 0.1) {

          cloudLabel[ind] = -1;//-1代表曲率很小的点
          surfPointsFlat.push_back(laserCloud->points[ind]);

          smallestPickedNum++;
          if (smallestPickedNum >= 4) {//只选最小的四个，剩下的Label==0,就都是曲率比较小的
            break;
          }

          cloudNeighborPicked[ind] = 1;
          for (int l = 1; l <= 5; l++) {//同样防止特征点聚集
            float diffX = laserCloud->points[ind + l].x 
                        - laserCloud->points[ind + l - 1].x;
            float diffY = laserCloud->points[ind + l].y 
                        - laserCloud->points[ind + l - 1].y;
            float diffZ = laserCloud->points[ind + l].z 
                        - laserCloud->points[ind + l - 1].z;
            if (diffX * diffX + diffY * diffY + diffZ * diffZ > 0.05) {
              break;
            }

            cloudNeighborPicked[ind + l] = 1;
          }
          for (int l = -1; l >= -5; l--) {
            float diffX = laserCloud->points[ind + l].x 
                        - laserCloud->points[ind + l + 1].x;
            float diffY = laserCloud->points[ind + l].y 
                        - laserCloud->points[ind + l + 1].y;
            float diffZ = laserCloud->points[ind + l].z 
                        - laserCloud->points[ind + l + 1].z;
            if (diffX * diffX + diffY * diffY + diffZ * diffZ > 0.05) {
              break;
            }

            cloudNeighborPicked[ind + l] = 1;
          }
        }
      }

      //将剩余的点（包括之前被排除的点）全部归入平面点中less flat类别中
      for (int k = sp; k <= ep; k++) {
        if (cloudLabel[k] <= 0) {
          surfPointsLessFlatScan->push_back(laserCloud->points[k]);
        }
      }
    }

    //由于less flat点最多，对每个分段less flat的点进行体素栅格滤波
    pcl::PointCloud<PointType> surfPointsLessFlatScanDS;
    pcl::VoxelGrid<PointType> downSizeFilter;
    downSizeFilter.setInputCloud(surfPointsLessFlatScan);
    downSizeFilter.setLeafSize(0.2, 0.2, 0.2);
    downSizeFilter.filter(surfPointsLessFlatScanDS);

    //less flat点汇总
    surfPointsLessFlat += surfPointsLessFlatScanDS;
  }

3 发布ROS消息

这里依次发布了消除运动畸变后的所有点云、较大曲率特征点、大曲率特征点、较小曲率特征点、小曲率特征点、以及IMU信息。当然，这里笔者觉得作者的迷惑行为在于用sensor_msgs::PointCloud2发布了IMU信息，所以为啥不直接用sensor_msgs::Imu？

  //publich消除非匀速运动畸变后的所有的点
  sensor_msgs::PointCloud2 laserCloudOutMsg;
  pcl::toROSMsg(*laserCloud, laserCloudOutMsg);
  laserCloudOutMsg.header.stamp = laserCloudMsg->header.stamp;
  laserCloudOutMsg.header.frame_id = "/camera";
  pubLaserCloud.publish(laserCloudOutMsg);

  //publich消除非匀速运动畸变后的平面点和边沿点
  sensor_msgs::PointCloud2 cornerPointsSharpMsg;
  pcl::toROSMsg(cornerPointsSharp, cornerPointsSharpMsg);
  cornerPointsSharpMsg.header.stamp = laserCloudMsg->header.stamp;
  cornerPointsSharpMsg.header.frame_id = "/camera";
  pubCornerPointsSharp.publish(cornerPointsSharpMsg);

  sensor_msgs::PointCloud2 cornerPointsLessSharpMsg;
  pcl::toROSMsg(cornerPointsLessSharp, cornerPointsLessSharpMsg);
  cornerPointsLessSharpMsg.header.stamp = laserCloudMsg->header.stamp;
  cornerPointsLessSharpMsg.header.frame_id = "/camera";
  pubCornerPointsLessSharp.publish(cornerPointsLessSharpMsg);

  sensor_msgs::PointCloud2 surfPointsFlat2;
  pcl::toROSMsg(surfPointsFlat, surfPointsFlat2);
  surfPointsFlat2.header.stamp = laserCloudMsg->header.stamp;
  surfPointsFlat2.header.frame_id = "/camera";
  pubSurfPointsFlat.publish(surfPointsFlat2);

  sensor_msgs::PointCloud2 surfPointsLessFlat2;
  pcl::toROSMsg(surfPointsLessFlat, surfPointsLessFlat2);
  surfPointsLessFlat2.header.stamp = laserCloudMsg->header.stamp;
  surfPointsLessFlat2.header.frame_id = "/camera";
  pubSurfPointsLessFlat.publish(surfPointsLessFlat2);

  //publich IMU消息,由于循环到了最后，因此是Cur都是代表最后一个点，即最后一个点的欧拉角，畸变位移及一个点云周期增加的速度
  pcl::PointCloud<pcl::PointXYZ> imuTrans(4, 1);
  //起始点欧拉角
  imuTrans.points[0].x = imuPitchStart;
  imuTrans.points[0].y = imuYawStart;
  imuTrans.points[0].z = imuRollStart;

  //最后一个点的欧拉角
  imuTrans.points[1].x = imuPitchCur;
  imuTrans.points[1].y = imuYawCur;
  imuTrans.points[1].z = imuRollCur;

  //最后一个点相对于第一个点的畸变位移和速度
  imuTrans.points[2].x = imuShiftFromStartXCur;
  imuTrans.points[2].y = imuShiftFromStartYCur;
  imuTrans.points[2].z = imuShiftFromStartZCur;

  imuTrans.points[3].x = imuVeloFromStartXCur;
  imuTrans.points[3].y = imuVeloFromStartYCur;
  imuTrans.points[3].z = imuVeloFromStartZCur;

  sensor_msgs::PointCloud2 imuTransMsg;
  pcl::toROSMsg(imuTrans, imuTransMsg);
  imuTransMsg.header.stamp = laserCloudMsg->header.stamp;
  imuTransMsg.header.frame_id = "/camera";
  pubImuTrans.publish(imuTransMsg);

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C/C++教程

loam源码解析： scanRegistration（二）

scanRegistration.cpp解析二

六、点云回调函数laserCloudHandler

1 遍历点云中每一个点，进行校正

1.1 如果收到IMU数据,使用IMU矫正点云畸变：

1.2 将每个点放入对应线号的容器

2 去除不靠点，提取特征点

2.1 计算各个点云点的曲率

2.2 筛选特征点

2.3 提取特征点

3 发布ROS消息

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数据库

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人工智能

区块链

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loam源码解析 ： scanRegistration（二）

scanRegistration.cpp解析二

六、点云回调函数laserCloudHandler

1 遍历点云中每一个点，进行校正

1.1 如果收到IMU数据,使用IMU矫正点云畸变：

1.2 将每个点放入对应线号的容器

2 去除不靠点，提取特征点

2.1 计算各个点云点的曲率

2.2 筛选特征点

2.3 提取特征点

3 发布ROS消息

前端开发

后端开发

移动端开发

数据库

服务器运维

人工智能

区块链

游戏开发

网站运营

大数据/云计算

软件工程

软件/开发工具使用

资讯

loam源码解析： scanRegistration（二）