118 lines
3.9 KiB
Markdown
118 lines
3.9 KiB
Markdown
# RPLIDAR A1 — LIDAR Container
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ROS 2 container for the Slamtec RPLIDAR A1, built on top of a fork of the
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official `sllidar_ros2` driver.
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---
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## Architecture
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```
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┌──────────────────────────────────────┐
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│ sllidar_ros2 (rplidar_node) │
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│ │
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│ serial 115200 baud │
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│ angle_compensate = true │
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│ scan_mode = Sensitivity │
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│ ▼ │
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│ /dev/ttyUSB0 ──────> RPLIDAR A1 │
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│ │
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/scan <───────│ LaserScan @ ~10 Hz │
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(sensor_msgs/ │ 360° scan, range 0.15–12 m │
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LaserScan) │ │
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└──────────────────────────────────────┘
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```
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---
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## How the build works
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The driver source lives in `lidar/sllidar_ros2/` as a **git subtree** of this
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repository. The [Dockerfile](Dockerfile) copies it directly from the
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workspace — no network access is required at build time.
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```
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Workspace repo Docker build
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────────────────────────── ──────────────────────────────────────────
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lidar/sllidar_ros2/ ───> COPY lidar/sllidar_ros2/ src/sllidar_ros2/
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(git subtree of fork) colcon build --packages-select sllidar_ros2
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```
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The upstream fork is maintained at:
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https://github.com/m5p3nc3r/sllidar_ros2
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---
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## Development workflow
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### Pulling upstream changes into the workspace
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```bash
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git subtree pull --prefix=lidar/sllidar_ros2 sllidar_ros2 main --squash
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```
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This fetches the latest commits from the fork, squashes them into a single
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merge commit, and updates `lidar/sllidar_ros2/` in the workspace.
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### Making local changes
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Edit files inside `lidar/sllidar_ros2/` as normal, then commit them to the
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workspace repo:
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```bash
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git add lidar/sllidar_ros2/
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git commit -m "lidar: describe the change"
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```
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### Pushing changes back to the fork
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```bash
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git subtree push --prefix=lidar/sllidar_ros2 sllidar_ros2 main
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```
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This replays only the commits that touched `lidar/sllidar_ros2/` and pushes
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them to the fork's `main` branch.
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### First-time setup on a fresh clone
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The subtree files are committed in the workspace repo, so a `git clone` of
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this repo is all that is needed — there is no separate step to initialise the
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subtree. To be able to pull or push to the fork later, add the remote:
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```bash
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git remote add sllidar_ros2 https://github.com/m5p3nc3r/sllidar_ros2.git
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```
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---
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## Changes relative to upstream
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| File | Change |
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| `src/sllidar_node.cpp` | `/scan` publisher QoS made configurable via `scan_qos_depth` (int) and `scan_qos_reliability` (`best_effort`\|`reliable`) parameters. Defaults to `best_effort`, depth 2 — required for Nav2 / RViz2 compatibility. |
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| `launch/sllidar_a1_launch.py` | Exposes `scan_qos_depth` and `scan_qos_reliability` as launch arguments. |
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The upstream Slamtec repository is at:
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https://github.com/slamtec/sllidar_ros2
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---
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## Published topics
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| Topic | Type | Description |
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| `/scan` | `sensor_msgs/LaserScan` | 360° laser scan, `BEST_EFFORT` QoS, depth 2 |
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## Device
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The RPLIDAR A1 connects via USB serial at `/dev/ttyUSB0` (default), 115200 baud.
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The container receives access to that device via the `devices` mapping in
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[docker-compose.yml](../docker-compose.yml). To use a different port, set
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`LIDAR_PORT` in your `.env` file:
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```bash
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LIDAR_PORT=/dev/ttyUSB1
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```
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