Camera

camera.py

Overview

camera.py is a horizontal sensor-stub component: a self-contained software camera that produces deterministic RGB + depth imagery even when no physical sensor is present. It lets downstream perception, fusion and visualisation nodes run in CI, headless simulation, or early prototyping environments where real hardware is unavailable.

Interfaces (strongly-typed, stateless)

Direction

Topic

Message type

Notes

Provided

/{robot}/camera

sensor_msgs/Image

Static BGR8 frame read from image.jpg

Provided

/{robot}/depth

sensor_msgs/Image

8-bit signed mono array (ones); same resolution as RGB

Both topics share identical header.stamp values and are published at 10 Hz, allowing time-synchronisation filters to treat them as a stereo pair.

Contract

Pre-conditions

  • The JPEG file exists and is readable.

  • Resolution ≤ 1920 × 1080 (soft real-time ceiling).

Post-conditions

  • The depth image’s height and width match the RGB frame exactly.

  • Header fields stamp and frame_id are identical between colour and depth messages.

Invariants

  • Latency (JPEG load → publish) ≤ 8 ms on a 4-core laptop.

  • Peak RAM ≤ 2 × (W × H × 3) bytes (one colour buffer + one depth buffer).

Protocol

This component is stateless: each 100 ms cycle publishes fresh, independent messages.

Lifecycle

  • Node name {robot}_camera

  • Ready once its publishers are advertised (no init service).

  • Clean shutdown on Ctrl-C or rosnode kill.

Quality & Reusability metrics

Latency < 8 ms | Throughput = 10 Hz | Cyclomatic complexity < 10

Directory layout

camera.py expects the JPEG at

/root/Desktop/cogar_ass1/cogar_ws/src/tiago1/scripts/image.jpg

Update the path if you move the file; no other configuration is required.

camera.publish()[source]

Bootstrap the node and stream frames until ROS shuts down.

Execution flow

  1. Node init – registers with the ROS master under {robot}_camera.

  2. Publisher creation • pub_rgb → /{robot}/camera (BGR8 colour) • pub_depth → /{robot}/depth (8-bit signed mono)

  3. Main loop (10 Hz) a. Load the static JPEG each cycle (immediate visual edits propagate). b. Convert to sensor_msgs/Image via cv_bridge and publish. c. Allocate a matching depth array filled with ones, convert and

    publish.

    1. Sleep the remainder of the 100 ms period.

  4. Loop exits cleanly when rospy.is_shutdown() becomes True.

Exceptions

Any non-ROS exception aborts the node and prints a traceback, which is useful during development. ROS interruptions are swallowed in main.