82 lines
2.7 KiB
Markdown
82 lines
2.7 KiB
Markdown
# Unified USB Camera Launch Design
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## Goal
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Make the camera behavior of `hobot_usb_cam.launch.py` and
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`hobot_usb_cam_websocket.launch.py` identical. The WebSocket variant must add
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only the WebSocket service.
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## Configuration
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Add `config/usb_camera.yaml` as the single source of runtime camera parameters:
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- `video_device`: `/dev/video0`
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- `image_width`: `1280`
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- `image_height`: `720`
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- `framerate`: `30`
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- `pixel_format`: `mjpeg`
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- `io_method`: `mmap`
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- `zero_copy`: `false`
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- `frame_id`: `default_usb_cam`
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The calibration data remains in `usb_camera_calibration.yaml`; it is not mixed
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with ROS runtime parameters. The shared base launch resolves its installed path
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and applies it to the camera node after loading the runtime YAML. Both launch
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variants therefore receive the same calibration path without a source-tree
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absolute path.
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## Launch Structure
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`hobot_usb_cam.launch.py` will:
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1. Declare one `camera_config` launch argument whose default is the installed
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`config/usb_camera.yaml` path.
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2. Start the shared-memory environment once.
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3. Resolve the installed `usb_camera_calibration.yaml` path.
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4. Start one `hobot_usb_cam` node with the YAML file as its parameter source and
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the resolved calibration resource path.
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`hobot_usb_cam_websocket.launch.py` will:
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1. Include `hobot_usb_cam.launch.py` without overriding camera parameters.
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2. Include the WebSocket launch configured for `/image`, MJPEG input, image-only
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display, and a 30 FPS output limit.
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It will not start `hobot_codec`, duplicate the shared-memory launch, or carry
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camera parameter literals.
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## Data Flow
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Without WebSocket:
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`/dev/video0 -> hobot_usb_cam -> /image (CompressedImage)`
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With WebSocket:
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`/dev/video0 -> hobot_usb_cam -> /image (CompressedImage) -> WebSocket`
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No RGB conversion or second JPEG encode is performed.
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## Validation
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An automated structural check will verify that:
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- the YAML contains the required 1280x720, 30 FPS, native MJPEG parameters;
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- the base launch loads that YAML;
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- the WebSocket launch includes the base launch;
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- the WebSocket launch does not define a camera node, codec node, or camera
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parameter overrides.
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After building, each launch will be started separately. Both must publish one
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`sensor_msgs/msg/CompressedImage` topic at approximately 30 FPS with decoded
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dimensions of 1280x720. Only the WebSocket launch may create the WebSocket node
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and port 8080 service.
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## Operational Notes
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The two launch files cannot run concurrently because they both own
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`/dev/video0`. Runtime validation is sequential and stops the first launch
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before starting the second. Any separately started `usb_cam_node_exe` must also
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be stopped before validation because V4L2 permits only one active capture owner
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for this camera.
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