baselink2imu and baselink2lidar are reversed

[VRichardJP]

Despites their name, both baselink2imu and baselink2lidar are used as imu->baselink and lidar->baselink transformations in the code.

For example, this line:

direct_lidar_inertial_odometry/src/dlio/odom.cc

Line 1386 in 77b3563

Eigen::Vector3f ang_vel_cg = this->extrinsics.baselink2imu.R * ang_vel;

converts IMU angular velocity measurement into baselink frame.

Another example:

direct_lidar_inertial_odometry/src/dlio/odom.cc

Lines 575 to 576 in 77b3563

	pcl::transformPointCloud (*this->original_scan, *deskewed_scan_,
	this->T_prior * this->extrinsics.baselink2lidar_T);

Here, the original LIDAR scan (so in lidar frame) is first transformed by baselink2lidar, as if it was "lidar->baselink".

Not only it makes the code confusing, but it is also easy to miswrite the transforms in the dlio.yaml file. I think it would be better to rename these transforms to lidar2baselink and imu2baselink:

$ grep -rIl baselink2lidar | xargs sed -i 's/baselink2lidar/lidar2baselink/g'
$ grep -rIl baselink2imu | xargs sed -i 's/baselink2imu/imu2baselink/g'

?

[kennyjchen]

Good point -- technically yes they represent the transformation from sensor to baselink. Sorry for the confusion.