Rosbags

Warnings

• breaking The import paths for serialization/deserialization modules were refactored, specifically affecting imports from `rosbags.serde.serdes`. Code relying on these old paths will break.
  Fix: Update your imports to the new structure, typically importing directly from `rosbags.serde` or using the high-level `AnyReader` and its `deserialize` method which handles these internally. The official documentation's quickstart demonstrates the recommended approach using `rosbags.highlevel` and `rosbags.typesys`.
• gotcha When reading rosbag files, especially those without embedded message definitions or containing custom message types, `rosbags` requires an explicit `Typestore` to correctly deserialize messages. Failing to provide an appropriate `default_typestore` can lead to deserialization errors or incorrect message interpretation.
  Fix: Always provide a `default_typestore` (e.g., `get_typestore(Stores.ROS2_FOXY)`) to `AnyReader` or `Reader` instances. For custom message types, ensure they are registered with the `Typestore` or included in a custom message definition path.
• gotcha While `rosbags` itself is designed for efficient handling of bag files, processing extremely large rosbag files (e.g., hundreds of GBs or millions of messages) without care can still lead to high memory consumption, especially if users attempt to load all messages or connections into memory simultaneously. Iterators are provided for a reason.
  Fix: Utilize the iterator-based approach (e.g., `reader.messages()`) to process messages one by one rather than loading all messages at once. Filter connections using `reader.connections` to only process relevant topics. Ensure your processing logic within the loop is memory-efficient.

Install

• pip install rosbags Install latest version

Imports

• AnyReader

  from rosbags.highlevel import AnyReader

  Primary high-level interface for reading rosbag files.
• Stores

  from rosbags.typesys import Stores

  Used to access predefined message type stores (e.g., ROS2_FOXY).
• get_typestore

  from rosbags.typesys import get_typestore

  Function to retrieve a message type store.
• Reader

  from rosbags.rosbag2 import Reader

  Specific reader for ROS2 bag files when high-level AnyReader is not sufficient.
• Serde

  from rosbags.serde import Serde

  The import path for Serde-related modules changed. Direct import from `rosbags.serde` is now preferred. Older paths like `rosbags.serde.serdes` were deprecated around version 0.9.20.

Quickstart

This quickstart demonstrates how to open a rosbag file (ROS1 or ROS2), iterate through its messages, and deserialize them using the high-level `AnyReader` interface. It includes explicit handling for type stores, which is crucial for correct message deserialization, especially if the bag does not contain complete message definitions or for custom message types. Remember to replace `test_rosbag_dir` with the actual path to your rosbag.

from pathlib import Path
from rosbags.highlevel import AnyReader
from rosbags.typesys import Stores, get_typestore

# Replace with the actual path to your rosbag file/directory
# For testing, you can create a dummy bag file or use an existing one.
# Example: bagpath = Path('./path/to/my_rosbag')
# Ensure the path points to the directory containing a ROS2 bag or a ROS1 .bag file.
bagpath = Path('test_rosbag_dir') # Placeholder, modify as needed

# Create a type store to use if the bag has no message definitions or for custom types.
# ROS2_FOXY is an example; choose the appropriate ROS distribution if needed.
typestore = get_typestore(Stores.ROS2_FOXY)

try:
    # Create reader instance and open for reading.
    with AnyReader([bagpath], default_typestore=typestore) as reader:
        # Filter connections (topics) if desired. Here, we read all messages.
        # connections = [x for x in reader.connections if x.topic == '/imu_raw/Imu']
        
        print(f"Found {len(reader.connections)} connections (topics) in the bag.")
        for connection in reader.connections:
            print(f"  Topic: {connection.topic}, Type: {connection.msgtype}")

        message_count = 0
        for connection, timestamp, rawdata in reader.messages():
            # Deserialize the message data
            msg = reader.deserialize(rawdata, connection.msgtype)
            # Access message fields (example for a common message type)
            # This assumes your message type has a 'header' and 'frame_id'
            # Adapt based on the actual message types in your bag.
            try:
                if hasattr(msg, 'header') and hasattr(msg.header, 'frame_id'):
                    print(f"[{timestamp}] Topic: {connection.topic}, Frame ID: {msg.header.frame_id}")
                else:
                    print(f"[{timestamp}] Topic: {connection.topic}, Message: {msg}")
            except AttributeError:
                print(f"[{timestamp}] Topic: {connection.topic}, Message: {msg}") # Fallback for messages without header
            message_count += 1
            if message_count >= 10: # Limit output for brevity
                print("... (truncated after 10 messages)")
                break
except FileNotFoundError:
    print(f"Error: Bag file or directory not found at {bagpath}. Please create or specify a valid path.")
except Exception as e:
    print(f"An error occurred: {e}")