Module 07 · Phase 3: Sensor integration
Sensor Time Synchronization & Latency Engineering
Separate clock synchronization, measurement synchronization, transport latency and processing latency, then measure and fix each.
This overview is open. 6 of 6 guides are written; the others show Coming soon until they are complete and tested.
Questions this module answers
- How do I synchronize camera, LiDAR and IMU?
- What happens if camera data is 50 ms late?
- How do I measure timestamp offsets and find dropped or out-of-order messages in a ROS bag?
- How do I deskew a LiDAR scan and compensate for delayed measurements?
What it covers
- Hardware sync: PPS, PTP
- Clock domains and sensor vs ROS 2 timestamps
- message_filters and ApproximateTime
- Mixed update rates
- Transport and processing latency
- Out-of-order and delayed data
- LiDAR motion distortion and deskewing
Guides and design decisions
A. Engineering Guides (5)
B. Design & Selection (1)
Diagnostics, tools and challenges
C. Troubleshooting (4)
- Sensor timestamps are inconsistentStamps jump, run backwards or differ from the ROS clock.
- Camera data is delayedImages lag the other sensors by a constant or growing amount.
- IMU and LiDAR frequencies do not matchFusion drops or interpolates data at mismatched rates.
- Localization fails due to timestamp offsetsThe estimator diverges only when the robot rotates quickly.
D. Interactive tools (1)
- Sensor Time Synchronization SimulatorCamera, LiDAR and IMU timelines with offsets, rates and delays, and what they do to localization.
E. Design challenges (2)
- Challenge 2: Outdoor-to-Indoor Autonomous NavigationGNSS outdoors to LiDAR-inertial or visual-inertial indoors: sensor and frame architecture, sync, calibration, estimation, handover and recovery.
- Challenge 4: UAV GNSS-Denied NavigationCamera, LiDAR and IMU on a UAV: compute, calibration, VIO/LIO, estimation, flight-controller integration and failure handling.
Practical deliverables
- Timestamp analysis tool
- Sensor synchronization simulator
- ROS 2 configuration examples
- Latency debugging checklist
Read first: existing FixTheRobot lessons and labs
This module builds on these instead of repeating them.
- Sensor Calibration and Synchronization SLAM · Lesson
- Sensor Topics and Message Timing SLAM · Lesson
- Diagnose Sensor Timestamp Problems SLAM · Lab
- Diagnose Camera–IMU Synchronization Errors SLAM · Lab
- Coordinate Alignment and Timestamps Perception · Lesson