Software Requirements Odometry System

3.4 Odometry System

3.4.1 Objectives

• Fuse odometry, IMU, GPS, and ZED VO for accuracy.
• Provide local and global pose via EKF.
• Visualize in Mapviz and diagnostics tools.
• Remain reliable under partial sensor loss.

3.4.2 Functional Requirements

FR-4.1 Sensor Data Integration

• Encoders → baseline odom.
• IMU reduces short-term drift.
• GPS corrects long-term drift.
• ZED2i VO as additional source.
• All data time-synchronized via headers.

FR-4.2 State Estimation (EKF Fusion)

• FR-4.2.1 Local EKF fuses encoders + IMU → /localization/odom_local (odom frame).
• FR-4.2.2 Global EKF fuses local EKF + GPS + ZED VO → /localization/odom_global (map frame) and publishes map↔odom.
• FR-4.2.3 navsat_transform consumes local orientation (from local EKF/IMU) + GPS → /localization/navsat/odometry (world frame).
• FR-4.2.4 Publish standard /odom, /tf for other subsystems.
• FR-4.2.5 Graceful degradation under GPS loss (rely on local EKF).
• FR-4.2.6 Parameters in ekf_local.yaml, ekf_global.yaml.

FR-4.3 Visualization & Base Station Feedback

• Mapviz shows trajectory/position.
• Display local (odom_local) and global (odom_global) paths simultaneously.
• UI shows drift and sensor health.
• Logs include timestamped odom, EKF outputs, drift metrics (CSV export).

FR-4.4 Simulation & Testing

• Testable in RViz/Gazebo with simulated encoders/IMU/GPS/ZED.
• 100 m straight-line drift tests (sim + field) with bag/CSV.
• Validate EKF vs ground truth (e.g., GPS path).
• Automated scripts compute error, drift %, update rate.

3.4.3 Non-Functional Requirements

ID	Type	Requirement
NFR-4.1	Accuracy	Drift < 5% over 100 m under normal conditions.
NFR-4.2	Performance	Updates ≥ 30 Hz.
NFR-4.3	Reliability	Stable estimates during temporary sensor dropouts.
NFR-4.4	Robustness	Handle failures (continue with IMU+encoders when GPS absent).
NFR-4.5	Testability	Configurable logging for inputs and EKF outputs.

3.4.4 Verification Criteria

• Local EKF drift < 2% (short-term sim + field).
• Global EKF integrates GPS + ZED VO for long-term accuracy.
• Total drift < 5% over 100 m straight-line.
• Mapviz shows local/global estimates at ≥ 30 Hz.
• Sim confirms EKF performance/parameter stability pre-hardware.