VINS-Mono on Airsim

This repository aims to implement the state of the art monocular VI-SLAM, VINS-Mono over Microsoft virtual environment Airsim. The whole setup runs on UnReal Engine4 and has been tested over Blocks environment.

Building the packages

1. $ cd catkin_vins/src/Airsim/ && ./clean.sh && ./setup.sh
2. $ ./build && cd ../../../
3. $ cd catkin_vins && catkin build && cd ..
4. $ sudo chmod +x run_all.sh

Running the package

[NOTE] : This package already runs binary located at ~/Airsim_Binaries/HiFi_3ftMarker/HiFi_3ftMarker/LinuxNoEditor/Blocks.sh, Feel free to change it to your binary

Pre-requisite:

• install xterm to run following scripts
• put the settings.json file in Documents folder
• pip install -r requirements.txt (advisable to create a new conda environment)

Command:
$ ./run_all.sh

[NOTE] : This script uses a pre-set navigation file (see last command in run_all script). In order to run with SITL, changing the Settings.json for blocks to operate on ArduPilot ports and then giving the navigation commands would do.

Error Evaluation

Error plots have been generated from RPG_trajectory Github repository

1. Record a bag file while running the repository
2. $ python bag2plots.py <Address_to_bag_file>

You'll have your plots at error_evaluation/plots

Aligned Plots for a different trajectory looks like this

Closing everything

$ killall xterm Blocks

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Important parameters

All tunable parameters are placed in catkin_vins/src/config/airsim/airsim_config.yaml

These parameters are listed by the modules they'll be affecting

Camera Module

Image width and height: published images dimension must match the one in config file. Distortion Parameter : In traditional setting, they along with extruinsics, intrinsics are obtained by camera calibration. They are taken to be 0 for OpenGL based applications (Airsim). Camera Intrinsic Parameters : Intrinsic matrix of camera in use. For pinhole camera see this. For pin-hole camera model, it depends on image width, height, FOV. For this implementation FOV is set to 90 degrees. Camera Extrinsic Matrix (Rotation/Translation) : The relative position of IMU(body) from camera. It must be noted that camera's co-ordinate frame is rotated with respect to IMU/body's co-ordinate frame in airsim. The orientation for front camera with no pitch, roll, yaw is as shown:

Feature Tracking

• Maximum number of features : Sets a high bar for selection fo features. This indirectly keeps the optimization algorithm in check.

• Minimum Distance between features : This parameter ensures that features are not detected in form of clusters and hence maintain sparcity of features selected for better motion approximation.

• Frequency of publishing : Sets a higher bar for sampling and publishing odometry data by the VINS system.

• Ransac threshold : Governs outlier rejection of features based on parallax difference

Optimizer

• Maximum Solver time : Keeps the algorithm real time and also affects highest sampling frequency that can be set.

• Maximum Solver Iteration : Same as above meanwhile putting a limit of accuracy attained.

• Threshold Parallax difference : Sets the minimum parallax difference for a new camera frame to be classified as keyframe

IMU Pre-integration

These all are initial estimates and would be updated as the drone moves.

• IMU accelerometer bias estimate standard deviation : std-deviation within which IMU's accelerometer bias is expected to lie.

• IMU gyroscopic bias estimate standard deviation : std-deviation within which IMU's gyroscopic bias is expected to lie.

• IMU accelerometer noise standard deviation : std-deviation within which IMU's accelerometer noise is expected to lie.

• IMU gyroscopic noise standard deviation : std-deviation within which IMU's gyroscopic noise is expected to lie.

• Temporal calibration (td) : Initial estimate of time delay between camera frame capture and corresponding IMU measurement record. (imu_timestamp - camera_timestamp)

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Possible errors and their solutions

• Error : Build error> different path in rpc_wrapper repository airsim

• Solution : Delete current build,devel,log directories. cd catkin_vins/src/Airsim && ./clean.sh && ./setup.sh && ./build.sh

• Error : Error in running move_on_path2.py or publish_path.py script

• Solution : Remove all versions of other dependencies (specially tornado), install only one version of all dependencies (for tornado it is 4.5.3. Tornado 6 is not supported)

• Error : No data recieved in VINS

• Solution : Check if published IMU and Image topic same as in catkin_vins/src/config/airsim/airsim_config.yaml

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Incase of any query please contact:

Ritvik Pandey (Intern H402743)

7478006888

ritvik.pandey03@gmail.com

This repository has been compiled for Honeywell India