trajectory-overlay

A collection of scripts to overlay videos with trajectories from a motion capture system.

Note: This is still heavily work in progress.

Instructions

1. Intrinsic calibration

If you use a camera for which no intrinsic calibration file is provided, you will need to record a video of the calibration pattern in data. The script intrinsic_calibration.py will guide you through the calibration process and save the results into a json file.

Note that the intrinsic calibration parameters depend on the image resolution. Make sure you use the same settings as you will use to record the video on which trajectories will be drawn.

2. Extrinsic calibration

To determine the pose of the camera in the world frame, you will need to place at least 6 markers in the motion capture arena and write their positions into a json file as follows:

{ 
    "pos": [[-1.459,  0.924, 0.014],
            [ 0.891,  1.781, 0.007],
            [ 3.049,  1.801, 0.011],
            [ 3.513, -1.529, 0.014],
            [ 1.262, -1.794, 0.007],
            [-1.124, -1.865, 0.010]]
}

Take a video of this setup and do not move the camera/phone anymore. Use the script extrinsic_calibration.py to compute and save the extrinsic calibration into a json file. Make sure to visually check the reprojection of the markers (green). If they are totally off the intrinsic calibration is likely to be inaccurate.

You can call extrinsic_calibration.py as follows:

python extrinsic_calibration.py <video_path> <markers_file_path> <intrinsic_calib_file_path>

Optional arguments are:

• --output <output_folder>

3. Overlay plot

Finally you can use plotter.py to overlay trajectories on a video. The script expects the trajectories to be saved in a hdf5 file. This hdf5 file should contain a separate group for each trajectory (each drone/vehicle). Each group should contain a dataset called pos. This dataset should be a N x 4 array where each row consists of [unix timestamp, x, y, z].

You can call plotter.py as follows:

python plotter.py <video_path> <log_trajectories_path> <intrinsic_calib_file_path>

Optional arguments are:

• --intrinsic_calib <intrinsic_calib_file_path>
• --extrinsic_calib <extrinsic_calib_file_path>
• --output <output_folder>