- Making camera arrival timestamps a hair less garbage.
- Estimates the absolute time offset between the camera and a ridgidly attached IMU
Under the skin the system is just a central difference kalman filter.
- It assumes a constant camera framerate and uses this to get rid of some of the jitter from arrival times
- Absolute offsets are calculated by aligning the IMU's measured angular velocity to that perceived by a simple Lucas-Kanade tracker running on the camera images. Obviously this will only work on systems that undergo significant movement.
This filter is pretty new and only tested on a couple of datasets I had lying around, so expect some issues when you first run it.
| Parameter | Description | Default |
|---|---|---|
stamp_on_arrival |
If true it will throw out the image timestamps and replace them with arrival times. | false |
max_imu_data_age_s |
How long in seconds to keep IMU data, the camera timing offset needs to be in this range. | 2.0 |
delay_by_n_frames |
Delays putting camera images into the filter by this many frames. Used to ensure there are plenty of IMU messages ahead of the frame to get IMU messages from. Note this does not cause any delay in the output of timesynced images. | 3 |
focal_length |
The focal length of the camera. A rough guess is fine and the system seems to run ok on distorted images | 460 |
use_pointcloud |
Uses pointcloud as input rather then an image. In this mode ICP matiching is used to estimate the rotation | false |
calc_offset |
If true the absolute time offset between the camera and an IMU is calculated. If false only some dejittering is performed (this saves a lot of CPU and most of the above parameters don't apply). | true |
| Parameter | Description | Default |
|---|---|---|
verbose |
Prints a large amount of information about the filters internal state | false |
mah_threshold |
Mahalanobis distance theshold for accepting measurement updates | 10.0 |
inital_delta_t |
Inital estimate in seconds for rate at which images are received. Set to 1/framerate. Note if you set it too small by a factor of 2 or more the automatic frame drop detection will cause weird effects | 0.05 |
inital_offset |
Inital estimate in seconds for the offset between the camera and IMU timestamps | 0.0 |
inital_timestamp_sd |
Inital standard deviation of systems timestamp in seconds (which is initalized to the first images timestamp) | 0.1 |
inital_delta_t_sd |
Inital standard deviation of the time between frames | 0.1 |
inital_offset_sd |
Inital standard deviation of the offset between the camera and IMU | 0.1 |
timestamp_sd |
Standard deviation of the received image timestamps | 0.02 |
angular_velocity_sd |
Standard deviation of the angular velocity estimated from the camera images | 0.03 |
delta_t_sd |
Standard deviation of the process noise for the time between frames | 0.0001 |
offset_sd |
Standard deviation of the process noise for the time offset between the IMU and camera | 0.0001 |