LIO-SAM代码问题汇总

LIO-SAM代码问题汇总

1

这是imu到相机坐标系的外参吗，这个map的强制数据类型转换也没看懂。

extRot = Eigen::Map<const Eigen::Matrix<double, -1, -1, Eigen::RowMajor>>(extRotV.data(), 3, 3); extRPY = Eigen::Map<const Eigen::Matrix<double, -1, -1, Eigen::RowMajor>>(extRPYV.data(), 3, 3);
extTrans = Eigen::Map<const Eigen::Matrix<double, -1, -1, Eigen::RowMajor>>(extTransV.data(), 3, 1);
extQRPY = Eigen::Quaterniond(extRPY);

2

为什么rotate acceleration、rotate gyroscope和rotate rpy不一样

sensor_msgs::Imu imu_out = imu_in;
// rotate acceleration
Eigen::Vector3d acc(imu_in.linear_acceleration.x, imu_in.linear_acceleration.y, imu_in.linear_acceleration.z);
acc = extRot * acc;
imu_out.linear_acceleration.x = acc.x();
imu_out.linear_acceleration.y = acc.y();
imu_out.linear_acceleration.z = acc.z();
// rotate gyroscope
Eigen::Vector3d gyr(imu_in.angular_velocity.x, imu_in.angular_velocity.y, imu_in.angular_velocity.z);
gyr = extRot * gyr;
imu_out.angular_velocity.x = gyr.x();
imu_out.angular_velocity.y = gyr.y();
imu_out.angular_velocity.z = gyr.z();
// rotate roll pitch yaw
Eigen::Quaterniond q_from(imu_in.orientation.w, imu_in.orientation.x, imu_in.orientation.y, imu_in.orientation.z);
Eigen::Quaterniond q_final = q_from * extQRPY;
imu_out.orientation.x = q_final.x();
imu_out.orientation.y = q_final.y();
imu_out.orientation.z = q_final.z();
imu_out.orientation.w = q_final.w();

3

这里cloud_infoConstPtr根本没有定义过，为什么还可以用

void laserCloudInfoHandler(const lio_sam::cloud_infoConstPtr& msgIn)
    {
        cloudInfo = *msgIn; // new cloud info
        cloudHeader = msgIn->header; // new cloud header
        pcl::fromROSMsg(msgIn->cloud_deskewed, *extractedCloud); // new cloud for extraction

        calculateSmoothness();

        markOccludedPoints();

        extractFeatures();

        publishFeatureCloud();
    }

4

判断为occluded points的判据没看懂 这个pointColInd的物理含义是什么

// occluded points
            float depth1 = cloudInfo.pointRange[i];
            float depth2 = cloudInfo.pointRange[i+1];
            int columnDiff = std::abs(int(cloudInfo.pointColInd[i+1] - cloudInfo.pointColInd[i]));

5

这是什么鬼构造方式

struct VelodynePointXYZIRT
{
    PCL_ADD_POINT4D
    PCL_ADD_INTENSITY;
    uint16_t ring;
    float time;
    EIGEN_MAKE_ALIGNED_OPERATOR_NEW
} EIGEN_ALIGN16;
POINT_CLOUD_REGISTER_POINT_STRUCT (VelodynePointXYZIRT,
    (float, x, x) (float, y, y) (float, z, z) (float, intensity, intensity)
    (uint16_t, ring, ring) (float, time, time)
)

6

没看懂，这是找imu时间戳

void findRotation(double pointTime, float *rotXCur, float *rotYCur, float *rotZCur)
    {
        *rotXCur = 0; *rotYCur = 0; *rotZCur = 0;

        int imuPointerFront = 0;
        while (imuPointerFront < imuPointerCur)
        {
            if (pointTime < imuTime[imuPointerFront])
                break;
            ++imuPointerFront;
        }

        if (pointTime > imuTime[imuPointerFront] || imuPointerFront == 0)
        {
            *rotXCur = imuRotX[imuPointerFront];
            *rotYCur = imuRotY[imuPointerFront];
            *rotZCur = imuRotZ[imuPointerFront];
        } else {
            int imuPointerBack = imuPointerFront - 1;
            double ratioFront = (pointTime - imuTime[imuPointerBack]) / (imuTime[imuPointerFront] - imuTime[imuPointerBack]);
            double ratioBack = (imuTime[imuPointerFront] - pointTime) / (imuTime[imuPointerFront] - imuTime[imuPointerBack]);
            *rotXCur = imuRotX[imuPointerFront] * ratioFront + imuRotX[imuPointerBack] * ratioBack;
            *rotYCur = imuRotY[imuPointerFront] * ratioFront + imuRotY[imuPointerBack] * ratioBack;
            *rotZCur = imuRotZ[imuPointerFront] * ratioFront + imuRotZ[imuPointerBack] * ratioBack;
        }
    }
    ```
### 7
lego-loam、lio-sam、loam都很像，那个坐标系转换以前就迷迷糊糊的看不懂，为什么有xyz坐标系与yzx坐标系转换这个步骤，是因为imu与velodyne的坐标系不一致吗，那为什么不在订阅imu话题的时候就把坐标系转换好了，这样后面都不用动了。