Crate r2a

R2A: Arrow bindings to ROS 2

This library provides utilities for mapping ROS messages to Arrow arrays. It heavily relies on the r2r library. Much like how r2r works, r2a RowBuilder and ArrowSupport implementations are automatically generated during build time and includes in the compilation. Before build, you must source your ROS 2 environment.

Features

• Convert ROS schema to Arrow fields.
• Support for 1-1 match and flat Arrow fields mapping. 1-1 match follows the exact structure of the original ROS message, while flat is a “more tabular” format.
• A row builder for storing converted rows.
• All ROS message schemas are supported as long as they are properly sourced.

Example

use r2a::ArrowSupport;
use r2a::RowBuilder;

let fields = r2r::std_msgs::msg::Header::arrow_fields(true); // If parameter is true, we also store an extra column called `message struct` that will include the complete message as a struct.
let mut row_builder = r2r::std_msgs::msg::Header::new_row_builder(fields.iter().collect()); //We keep all the fields, convert to Vec<&Field>

let my_message = r2r::std_msgs::msg::Header {
               stamp: r2r::builtin_interfaces::msg::Time {
                   sec: 0,
                   nanosec: 0,
               },
               frame_id: "test_frame".to_string(),
           };
row_builder.add_row(&my_message).unwrap();
let arrow_arrays = row_builder.to_arc_arrays();
//store to parquet, etc.

For more elaborate examples, see the examples in the Git repo.

When we create fields with arrow_fields and the RowBuilder new_row_builder, the message will keep it’s original structure. For example a sensor_msgs/msg/LaserScan message will be converted to Arrow like this:

header	angle_min	angle_max	angle_increment	time_increment	scan_time	range_min	range_max	ranges	intensities	message_struct
{‘stamp’: {‘sec’: 0, ‘nanosec’: 0}, ‘frame_id’: ‘test_frame’}	-1.57	1.57	0.01	0.001	0.05	0.2	10	[1. 2. 3. 4. 5.]	[0.5 0.7 0.9 1.1 1.3]	{‘header’: {‘stamp’: {‘sec’: 22, ‘nanosec’: 0}, ‘frame_id’: ‘test_frame’}, ‘angle_min’: -1.570, …}
{‘stamp’: {‘sec’: 1, ‘nanosec’: 0}, ‘frame_id’: ‘test_frame’}	-1.57	1.57	0.01	0.001	0.05	0.2	10	[1. 2. 3. 4. 5.]	[0.5 0.7 0.9 1.1 1.3]	{‘header’: {‘stamp’: {‘sec’: 28, ‘nanosec’: 0}, ‘frame_id’: ‘test_frame’}, ‘angle_min’: -1.570, …}

We can contrast that with flat_arrow_fields and new_flat_row_builder, there the same type of message will be converted like this:

header_stamp_sec	header_stamp_nanosec	header_frame_id	angle_min	angle_max	angle_increment	time_increment	scan_time	range_min	range_max	ranges	intensities	message_struct
0	0	test_frame	-1.57	1.57	0.01	0.001	0.05	0.2	10	[1. 2. 3. 4. 5.]	[0.5 0.7 0.9 1.1 1.3]	{‘header’: {‘stamp’: {‘sec’: 25, ‘nanosec’: 0}, ‘frame_id’: ‘test_frame’}, ‘angle_min’: -1.570, …}
1	0	test_frame	-1.57	1.57	0.01	0.001	0.05	0.2	10	[1. 2. 3. 4. 5.]	[0.5 0.7 0.9 1.1 1.3]	{‘header’: {‘stamp’: {‘sec’: 23, ‘nanosec’: 0}, ‘frame_id’: ‘test_frame’}, ‘angle_min’: -1.570, …}

Traits

ArrowSupport

The ArrowSupport trait is implemented for each ROS 2 message type, allowing the creation of row builders, Arrow schemas, and field definitions for that message type.

RowBuilder

The RowBuilder trait is implemented for each ROS 2 message type by a code generator. It serves as an accumulator that collects records and converts them into a collection of Arrow arrays. This trait is responsible for managing how records are added and stored and how they are converted into Arrow-compatible data structures.

Functions

get_supported_schemas

Returns an array of supported ROS message schemas. The list is automatically generated in compilation time.