sonar

sonar.py

Overview

sonar.py is a synthetic ultrasound range-finder component that emits constant sensor_msgs/Range messages at 10 Hz. It enables sensor-fusion, navigation and obstacle-avoidance pipelines to be exercised even without real hardware or ROS bags.

Interfaces (strongly-typed, stateless)

Direction	Topic	Message type / Notes
Provided	/{robot}/sonar	sensor_msgs/Range – single-beam, 10 Hz

Contract

Pre-conditions

• Node launched with a valid robot_id CLI argument.

• Downstream expects Range.ULTRASOUND readings at ∼10 Hz.

Post-conditions

• Publishes exactly one Range per loop iteration.

• range field is fixed at 3.0 m.

• Header uses frame_id “sonar” and current time stamp.

Invariants

• Loop frequency = 10 Hz ± 5%.

• field_of_view = 0.1 rad, min_range = 0.2 m, max_range = 4.0 m.

Quality-of-Service KPIs

Metric	Target	Rationale
Message rate	10 Hz ± 0.5 Hz	Keeps real-time filters stable.
Latency	< 50 ms	Avoids stale obstacle data.
CPU load	< 1 %	Safe on embedded CPUs.

Implementation notes

• Uses rospy.Rate(10) for timing.

• Message fields are hard-coded for simplicity; adjust constants below to emulate other sensors.

Functions

publish()

Advertise /sonar and stream constant Range messages until shutdown.