# Map Saver Config > --- name: map-saver-config description: 'Configure Nav2 map saver. Use when saving maps from SLAM, setting thresholds, or automatic periodic map saving.' --- # Nav2 Map Saver Configuration ## Overview The map saver (`nav2_map_server` package, `map_saver_server` executable) saves the current OccupancyGrid map to disk as a YAML + image file pair. It can be used via its service interface or the convenience CLI tool. The saved map can then be loaded by the map server for navigation. ## Map Saver Server Parameters ```yaml map_saver: ros__parameters: save_map_timeout: 2.0 # Timeout (seconds) waiting for map data when saving. free_thresh_default: 0.25 # Default free threshold written to the output YAML. occupied_thresh_default: 0.65 # Default occupied threshold written to the output YAML. map_subscribe_transient_local: true # Subscribe with TRANSIENT_LOCAL QoS to get latched maps. use_sim_time: false ``` ### QoS: TRANSIENT_LOCAL When `map_subscribe_transient_local: true`, the saver subscribes with `TRANSIENT_LOCAL` durability. This means it receives the last published map even if it connects after the map server published. This is the correct setting for saving maps published by map_server or SLAM Toolbox. Set to `false` only if your map publisher uses `VOLATILE` QoS. ## CLI Tool: map_saver_cli The simplest way to save a map: ```bash # Save to my_map.pgm + my_map.yaml in the current directory: ros2 run nav2_map_server map_saver_cli -f my_map # Save to a specific directory: ros2 run nav2_map_server map_saver_cli -f /home/robot/maps/floor1 # Save as PNG instead of PGM: ros2 run nav2_map_server map_saver_cli -f my_map --image-format png # Remap the map topic (if not default /map): ros2 run nav2_map_server map_saver_cli -f my_map --ros-args -r map:=/slam_toolbox/map # Set custom thresholds: ros2 run nav2_map_server map_saver_cli -f my_map --free 0.15 --occ 0.65 # Use sim time: ros2 run nav2_map_server map_saver_cli -f my_map --ros-args -p use_sim_time:=true ``` ### CLI Arguments | Argument | Description | |----------|-------------| | `-f, --output` | Output file base name (without extension) | | `--image-format` | `pgm` (default) or `png` | | `--free` | Free threshold (default 0.25) | | `--occ` | Occupied threshold (default 0.65) | | `--mode` | `trinary` (default), `scale`, or `raw` | | `-t, --map-topic` | Map topic to subscribe to (default `/map`) | ## Service Interface The map saver server exposes a service for programmatic saving: ```bash ros2 service call /map_saver/save_map nav2_msgs/srv/SaveMap \ "{map_topic: '/map', map_url: '/home/robot/maps/saved_map', \ image_format: 'pgm', map_mode: 'trinary', \ free_thresh: 0.25, occupied_thresh: 0.65}" ``` ### SaveMap.srv Definition ``` string map_topic # Topic to read the map from. string map_url # Output file path (base name, no extension). string image_format # "pgm" or "png". string map_mode # "trinary", "scale", or "raw". float32 free_thresh # Free threshold for the YAML. float32 occupied_thresh # Occupied threshold for the YAML. --- bool result # true = success. ``` ## CLI vs Service: When to Use Each | Use Case | Approach | |----------|----------| | Manual map save during development | CLI tool | | Automated periodic saves from a node | Service call | | Saving after mapping run completes | CLI tool | | Multi-floor save automation | Service call from a manager node | ## Saving SLAM Toolbox Maps For SLAM Toolbox, saving the OccupancyGrid (PGM) gives you a static map but **loses the pose graph**. To preserve the full graph state (for lifelong mode or localization mode): ```bash # Serialize the full graph: ros2 service call /slam_toolbox/serialize_map slam_toolbox/srv/SerializePoseGraph \ "{filename: '/home/robot/maps/house_map'}" ``` This produces `.posegraph` + `.data` files. You should save **both**: the serialized graph (for continued SLAM) and the PGM/YAML (for static navigation with AMCL). ## Output Files After running `map_saver_cli -f my_map`, you get: **my_map.yaml:** ```yaml image: my_map.pgm mode: trinary resolution: 0.05 origin: [-12.2, -10.7, 0.0] negate: 0 occupied_thresh: 0.65 free_thresh: 0.25 ``` **my_map.pgm:** A grayscale image where: - Pixel value 0 → occupied (black) - Pixel value 205 → free (light gray) - Pixel value 254 → unknown (near-white) ## Common Mistakes ### Saving Before the Map Is Stable If you save while SLAM is still building a submap, edges of the map will have partial/uncertain data. Wait until: - The robot has completed at least one loop closure. - No active submap construction is in progress at the area of interest. - The map has visually stabilized in RViz. ### Topic QoS Mismatch If the CLI hangs and times out, the QoS settings may not match: ```bash # Check the publisher's QoS: ros2 topic info /map --verbose ``` If the publisher uses `RELIABLE` + `TRANSIENT_LOCAL`, the saver must also use `TRANSIENT_LOCAL` (the default). If the publisher uses `BEST_EFFORT`, you need `map_subscribe_transient_local: false`. ### Wrong Map Topic SLAM Toolbox publishes on `/map` by default, but if you're running multiple SLAM instances or have remapped topics, specify the correct one: ```bash ros2 run nav2_map_server map_saver_cli -f my_map -t /slam_toolbox/map ``` ## Automated Periodic Saving (Python) ```python import rclpy from rclpy.node import Node from nav2_msgs.srv import SaveMap class PeriodicMapSaver(Node): def __init__(self): super().__init__('periodic_map_saver') self.client = self.create_client(SaveMap, '/map_saver/save_map') self.timer = self.create_timer(300.0, self.save_map) # Every 5 minutes. def save_map(self): if not self.client.wait_for_service(timeout_sec=2.0): self.get_logger().warn('Map saver service not available') return req = SaveMap.Request() req.map_topic = '/map' req.map_url = '/home/robot/maps/auto_save' req.image_format = 'pgm' req.map_mode = 'trinary' req.free_thresh = 0.25 req.occupied_thresh = 0.65 future = self.client.call_async(req) future.add_done_callback( lambda f: self.get_logger().info(f'Map saved: {f.result().result}')) ```