basalt/doc/Simulation.md

Simulator

For better evaluation of the system we use the simulated environment where the optical flow and IMU data is generated from the ground truth by adding noise.

Note: The path to calibration and configuration files used here works for the APT installation. If you compile from source specify the appropriate path to the files in data folder.

Visual-inertial odometry simulator

basalt_vio_sim --cam-calib /usr/etc/basalt/euroc_ds_calib.json --marg-data sim_marg_data --show-gui 1 

The command line options have the following meaning:

• --cam-calib path to camera calibration file. Check calibration instructions to see how the calibration was generated.
• --marg-data folder where the data from keyframe marginalization will be stored. This data can be later used for visual-inertial mapping simulator.
• --show-gui enables or disables GUI.

This opens the GUI and runs the sequence.

The buttons in the GUI have the following meaning:

• show_obs toggles the visibility of the ground-truth landmarks in the image view.
• show_obs_noisy toggles the visibility of the noisy landmarks in the image view.
• show_obs_vio toggles the visibility of the landmarks estimated by VIO in the image view.
• show_ids toggles the IDs of the landmarks.
• show_accel shows noisy accelerometer measurements generated from the ground-truth spline.
• show_gyro shows noisy gyroscope measurements generated from the ground-truth spline.
• show_gt_... shows ground truth position, velocity and biases.
• show_est_... shows VIO estimates of the position, velocity and biases.
• next_step proceeds to next frame.
• continue plays the sequence.
• align_se3 performs SE(3) alignment with ground-truth trajectory and prints the RMS ATE to the console.

Visual-inertial mapping simulator

basalt_mapper_sim --cam-calib /usr/etc/basalt/euroc_ds_calib.json --marg-data sim_marg_data --show-gui 1

The command line arguments are the same as above.

This opens the GUI where the map can be processed.

The system processes the marginalization data and extracts the non-linear factors from them. Roll-pitch and relative-pose factors are initially added to the system. One way to verify that they result in gravity-aligned map is the following

• optimize runs the optimization
• rand_inc applies a random increment to all frames of the system. If you run the optimize until convergence afterwards, and press align_se3 the alignment transformation should only contain the rotation around Z axis.
• rand_yaw applies an increment in yaw to all poses. This should not change the error of the optimization once is have converged.
• setup_points triangulates the points and adds them to optimization. You should optimize the system again after adding the points.
• align_se3 performs SE(3) alignment with ground-truth trajectory and prints the RMS ATE to the console.

For comparison we also provide the basalt_mapper_sim_naive executable that has the same parameters. It runs a global bundle-adjustment on keyframe data and inserts pre-integrated IMU measurements between keyframes. This executable is included for comparison only.