Coordinate 'Transformation' between poses

[YangSiri]

Hi, great LeGO contributors. A samll or maybe stupid question arises since i have been reading the codes: I notice the coordinate between the 'globalmap' and vlp is different. So the 'cloudkeypose6D' becomes weird while using it to build the map in ordinary laser-scanner frame. I see this 'transformation' many times in the codes and I think its pretty confusing. I start to wonder why would you do that. There's gotta be a reason, right?

Example 'transformation' in codes: odomAftMapped.header.stamp = ros::Time().fromSec(timeLaserOdometry); odomAftMapped.pose.pose.orientation.x = -geoQuat.y; odomAftMapped.pose.pose.orientation.y = -geoQuat.z; odomAftMapped.pose.pose.orientation.z = geoQuat.x; odomAftMapped.pose.pose.orientation.w = geoQuat.w; odomAftMapped.pose.pose.position.x = transformAftMapped[3]; odomAftMapped.pose.pose.position.y = transformAftMapped[4]; odomAftMapped.pose.pose.position.z = transformAftMapped[5];

_cloudKeyPoses3D->points[i].x = isamCurrentEstimate.at(i).translation().y(); cloudKeyPoses3D->points[i].y = isamCurrentEstimate.at(i).translation().z(); cloudKeyPoses3D->points[i].z = isamCurrentEstimate.at(i).translation().x();

            cloudKeyPoses6D->points[i].x = cloudKeyPoses3D->points[i].x;
            cloudKeyPoses6D->points[i].y = cloudKeyPoses3D->points[i].y;
            cloudKeyPoses6D->points[i].z = cloudKeyPoses3D->points[i].z;
            cloudKeyPoses6D->points[i].roll  = isamCurrentEstimate.at<Pose3>(i).rotation().pitch();
            cloudKeyPoses6D->points[i].pitch = isamCurrentEstimate.at<Pose3>(i).rotation().yaw();
            cloudKeyPoses6D->points[i].yaw   = isamCurrentEstimate.at<Pose3>(i).rotation().roll();_

void adjustOutlierCloud(){ PointType point; int cloudSize = outlierCloud->points.size(); for (int i = 0; i < cloudSize; ++i) { point.x = outlierCloud->points[i].y; point.y = outlierCloud->points[i].z; point.z = outlierCloud->points[i].x; point.intensity = outlierCloud->points[i].intensity; outlierCloud->points[i] = point; } }

Please some smart guy help me, thanks very much!

[YangSiri]

@TixiaoShan Brother?

[TixiaoShan]

Hi @YangSiri ,

Please refer to https://github.com/laboshinl/loam_velodyne/blob/0030b6a6b579fe2169ec36ffa939c7dd92f4275c/src/scanRegistration.cpp#L221 for the conversion. I followed their changes.

[YangSiri]

Yes, @TixiaoShan Thanks. I just want to know why they change the order of 'xyz'. Better calculation? Or more convient? And no offense, there is little notes for the codes... Looking forward to your explaination~

[andre-nguyen]

The original LOAM code has a lot of mysterious parts and you should probably not read it too much unless you want your eyes to bleed. The coordinate switching here probably has to do with projecting the lidar points in the camera frame. I believe that historically the "open source" LOAM was published as Ji Zhang was preparing V-LOAM.

[YangSiri]

Yes, @andre-nguyen ,i guess you're right. There is '/camera' in the codes. Do you know where does the function void transformAssociateToMap() come from? I mean the formula and theory stuff.

[andre-nguyen]

I mean the formula and theory stuff.

To the best of my knowledge, it solely exists within Ji Zhang's head and internally at Kaarta. Personally, reading it makes me think it was code-generated through matlab because no human could possibly write and understand such a horrible function... I think.

[YangSiri]

well, fair enough, thanks all of you.

[tejalbarnwal]

@andre-nguyen I apologize for asking such a silly query but is it like base_link is where the code assumes the lidar's frame and the camera can be treated as just another sensor attached to base_link if I wish to perform only Lidar Slam? While laser_odom represents the odometry of the lidar with respect to the camera_init frame? What does the camera_init frame signify? Also, how is the transform between the camera_init frame and the camera frame calculated?

[daohu527]

I'm going to optimize it, but at the moment why the coordinate system of lidar and imu is not explained clearly : )