README.md · hc/LeGO-LOAM

# LeGO-LOAM

This repository contains code for a lightweight and ground optimized lidar odometry and mapping (LeGO-LOAM) system for ROS compatible UGVs. The system takes in point cloud from a Velodyne VLP-16 Lidar (palced horizontal) and optional IMU data as inputs. It outputs 6D pose estimation in real-time. A demonstration of the system can be found here -> https://www.youtube.com/watch?v=O3tz_ftHV48


 <img src="/LeGO-LOAM/launch/demo.gif" alt="drawing" width="800"/>

## Dependency

- [ROS](http://wiki.ros.org/ROS/Installation) (tested with indigo, kinetic, and melodic)
- [gtsam](https://github.com/borglab/gtsam/releases) (Georgia Tech Smoothing and Mapping library, 4.0.0-alpha2)
  ```
  wget -O ~/Downloads/gtsam.zip https://github.com/borglab/gtsam/archive/4.0.0-alpha2.zip
  cd ~/Downloads/ && unzip gtsam.zip -d ~/Downloads/
  cd ~/Downloads/gtsam-4.0.0-alpha2/
  mkdir build && cd build
  cmake ..
  sudo make install
  ```

## Compile

You can use the following commands to download and compile the package.

```
cd ~/catkin_ws/src
git clone https://github.com/RobustFieldAutonomyLab/LeGO-LOAM.git
cd ..
catkin_make -j1
```
When you compile the code for the first time, you need to add "-j1" behind "catkin_make" for generating some message types. "-j1" is not needed for future compiling.

## The system

LeGO-LOAM is speficifally optimized for a horizontally placed VLP-16 on a ground vehicle. It assumes there is always a ground plane in the scan. The UGV we are using is Clearpath Jackal. It has a built-in IMU.

The package performs segmentation before feature extraction.

Lidar odometry performs two-step Levenberg Marquardt optimization to get 6D transformation.

## New Lidar

The key thing to adapt the code to a new sensor is making sure the point cloud can be properly projected to an range image and ground can be correctly detected. For example, VLP-16 has a angular resolution of 0.2&deg; and 2&deg; along two directions. It has 16 beams. The angle of the bottom beam is -15&deg;. Thus, the parameters in "utility.h" are listed as below. When you implement new sensor, make sure that the ground_cloud has enough points for matching. Before you post any issues, please read this.

```
extern const int N_SCAN = 16;
extern const int Horizon_SCAN = 1800;
extern const float ang_res_x = 0.2;
extern const float ang_res_y = 2.0;
extern const float ang_bottom = 15.0;
extern const int groundScanInd = 7;
```

Another example for Velodyne HDL-32e range image projection:

```
extern const int N_SCAN = 32;
extern const int Horizon_SCAN = 1800;
extern const float ang_res_x = 360.0/Horizon_SCAN;
extern const float ang_res_y = 41.333/float(N_Scan-1);
extern const float ang_bottom = 30.666666;
extern const int groundScanInd = 20;
```

One important thing to keep in mind is that our current implementation for range image projection is only suitable for sensors that have evenly distributed channels. For **KITTI** users, if you want to use our algorithm with Velodyne VLP-32c or **HDL-64e**, you need to write your own implementation for such projection. If the point cloud is not projected properly, you will lose many points and performance.

If you are using your lidar with an IMU, make sure your IMU is aligned properly with the lidar. The algorithm uses IMU data to correct the point cloud distortion that is cause by sensor motion. If the IMU is not aligned properly, the usage of IMU data will deteriorate the result. Ouster lidar IMU is not supported in the package.

## Run the package

1. Run the launch file:
```
roslaunch lego_loam run.launch
```
Notes: The parameter "/use_sim_time" is set to "true" for simulation, "false" to real robot usage.

2. Play existing bag files:
```
rosbag play *.bag --clock --topic /velodyne_points /imu/data
```
Notes: Though /imu/data is optinal, it can improve estimation accuracy greatly if provided. Some sample bags can be downloaded from [here](https://github.com/RobustFieldAutonomyLab/jackal_dataset_20170608).

## New data-set

This dataset, [Stevens data-set](https://github.com/TixiaoShan/Stevens-VLP16-Dataset), is captured using a Velodyne VLP-16, which is mounted on an UGV - Clearpath Jackal, on Stevens Institute of Technology campus. The VLP-16 rotation rate is set to 10Hz. This data-set features over 20K scans and many loop-closures.

## Cite *LeGO-LOAM*

Thank you for citing [our *LeGO-LOAM* paper](./Shan_Englot_IROS_2018_Preprint.pdf) if you use any of this code: 
```
@inproceedings{legoloam2018,
  title={LeGO-LOAM: Lightweight and Ground-Optimized Lidar Odometry and Mapping on Variable Terrain},
  author={Shan, Tixiao and Englot, Brendan},
  booktitle={IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)},
  pages={4758-4765},
  year={2018},
  organization={IEEE}
}
```

## Speed Optimization

An optimized version of LeGO-LOAM can be found [here](https://github.com/facontidavide/LeGO-LOAM/tree/speed_optimization). All credits go to @facontidavide. Improvements in this directory include but not limited to:

+ To improve the quality of the code, making it more readable, consistent and easier to understand and modify.
    + To remove hard-coded values and use proper configuration files to describe the hardware.
    + To improve performance, in terms of amount of CPU used to calculate the same result.
    + To convert a multi-process application into a single-process / multi-threading one; this makes the algorithm more deterministic and slightly faster.
    + To make it easier and faster to work with rosbags: processing a rosbag should be done at maximum speed allowed by the CPU and in a deterministic way.
    + As a consequence of the previous point, creating unit and regression tests will be easier.

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