Transforms

A fast, middleware-independent coordinate transform library for Rust.

Overview

transforms is a pure Rust library for managing coordinate transformations between different reference frames. It is designed for robotics and computer vision applications where tracking spatial relationships between sensors, actuators, and world coordinates is essential.

Key characteristics:

Middleware-independent: No ROS2, DDS, or any communication layer dependencies. Use it standalone or wrap it with your own pub-sub system. Checkout roslibrust_transforms if you are looking for a wrapped system.
no_std compatible: Works in embedded and resource-constrained environments.
Memory safe: Uses #![forbid(unsafe_code)] throughout.
Inspired by tf2: Familiar concepts for robotics developers, but with a Rust-first API.

Features

Transform Interpolation: Smooth interpolation between transforms at different timestamps using spherical linear interpolation (SLERP) for rotations and linear interpolation for translations.
Transform Chaining: Automatic computation of transforms between indirectly connected frames by traversing the frame tree.
Static Transforms: Transforms with the static timestamp value are treated as static (t=0 by default).
Time-based Buffer Management: Registry::with_max_age cleans up old transforms automatically; Registry::new keeps them until manual cleanup. Both work with and without std.
O(log n) Lookups: Efficient transform retrieval using BTreeMap storage.
Transformable Trait: Implement on your own types to make them transformable between coordinate frames.
Transform Into: Resolve and apply transforms directly from a Localized value with get_transform_for, eliminating manual frame and timestamp bookkeeping.

What's New

Full version history lives in CHANGELOG.md.

v2.0.0 highlights

Correct by construction: transforms are validated on insertion (finite values, unit rotations), the frame tree is strict (single pinned parent, no cycles), and lookups either answer the exact question asked or return an error — the silent-wrong-answer failure modes of 1.x are gone.
Real no_std: builds for bare-metal targets (CI proves it on thumbv7em-none-eabihf); the std feature is additive, and automatic cleanup (with_max_age) works in both modes.
Rust-first API cleanup: exact == with tolerant comparison in the approx traits, #[non_exhaustive] errors, private internals, optional serde support, an enforced panic policy, and MSRV 1.86.

add_transform is now fallible — the headline migration for 1.x users:

registry.add_transform(transform)?;

Installation

Add to your Cargo.toml:

[dependencies]
transforms = "2.0.0-beta.4"

Feature Flags

Feature	Default	Description
`std`	Yes	Enables `Timestamp::now()` and the `SystemTime` time type
`serde`	No	`Serialize`/`Deserialize` for the geometry and time types

Minimum supported Rust version: 1.86 (checked in CI).

Note on serde: Timestamp serializes its nanosecond value as a u128, which not every serde format supports (JSON via serde_json does). Deserialization does not validate — like hand-built transforms, deserialized ones are validated when they enter a Registry.

For no_std environments (requires a heap allocator; float math falls back to libm):

[dependencies]
transforms = { version = "2.0.0-beta.4", default-features = false }

Quick Start

use core::time::Duration;
use transforms::{
    geometry::{Quaternion, Transform, Vector3},
    time::Timestamp,
    Registry,
};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Create a registry with 60-second transform buffer
    let mut registry = Registry::with_max_age(Duration::from_secs(60));
    let timestamp = Timestamp::now();

    // Define a transform: sensor is 1 meter along X-axis from base
    let transform = Transform {
        translation: Vector3::new(1.0, 0.0, 0.0),
        rotation: Quaternion::identity(),
        timestamp,
        parent: "base".into(),
        child: "sensor".into(),
    };

    // Add and retrieve the transform
    registry.add_transform(transform)?;
    let result = registry.get_transform("base", "sensor", timestamp)?;

    println!("Transform: {result:?}");
    Ok(())
}

API Reference

Registry

// No automatic cleanup (also available via Default)
pub fn new() -> Self

// Automatic cleanup of transforms older than max_age
pub fn with_max_age(max_age: Duration) -> Self

pub fn add_transform(&mut self, transform: Transform<T>) -> Result<(), BufferError>
pub fn get_transform(&self, from: &str, to: &str, timestamp: T) -> Result<Transform<T>, TransformError>
pub fn get_transform_for<U: Localized<T>>(&self, value: &U, target_frame: &str) -> Result<Transform<T>, TransformError>
pub fn get_transform_at(&self, target_frame: &str, target_time: T, source_frame: &str, source_time: T, fixed_frame: &str) -> Result<Transform<T>, TransformError>
pub fn delete_transforms_before(&mut self, timestamp: T)
pub fn remove_frame(&mut self, child: &str) -> bool

Core Types

Type	Description
`Transform<T = Timestamp>`	Rigid body transformation (translation + rotation + timestamp + frames)
`Vector3`	3D vector with x, y, z components (f64)
`Quaternion`	Quaternion for rotations (expected unit norm) with w, x, y, z components (f64)
`Timestamp`	Time representation in nanoseconds (u128)
`TimePoint`	Trait for custom timestamp types used by `Transform`, `Buffer`, and `Registry`
`Point`	Example transformable type with position, orientation, timestamp, frame

For complete API documentation, see docs.rs/transforms.

Architecture

The library is organized around three core components:

┌─────────────────────────────────────────────────────────┐
│                       Registry                          │
│  ┌─────────────────────────────────────────────────┐    │
│  │  HashMap<child_frame, Buffer>                   │    │
│  │  ┌─────────────┐  ┌─────────────┐               │    │
│  │  │ Buffer "b"  │  │ Buffer "c"  │  ...          │    │
│  │  │ parent: "a" │  │ parent: "b" │               │    │
│  │  │ ┌─────────┐ │  │ ┌─────────┐ │               │    │
│  │  │ │Transform│ │  │ │Transform│ │               │    │
│  │  │ │  @ t=1  │ │  │ │  @ t=1  │ │               │    │
│  │  │ │Transform│ │  │ │Transform│ │               │    │
│  │  │ │  @ t=2  │ │  │ │  @ t=2  │ │               │    │
│  │  │ └─────────┘ │  │ └─────────┘ │               │    │
│  │  └─────────────┘  └─────────────┘               │    │
│  └─────────────────────────────────────────────────┘    │
└─────────────────────────────────────────────────────────┘

Registry

The main interface for managing transforms. It stores Buffer instances (one per child frame) and handles:

Adding new transforms
Retrieving transforms between any two frames (with automatic chaining)
Traversing the frame tree to compute indirect transforms
Automatic cleanup of expired transforms (with Registry::with_max_age)

Buffer

Time-indexed storage for transforms between a specific child-parent frame pair. Uses a BTreeMap<T, Transform<T>> for O(log n) lookups with automatic interpolation for timestamps between stored values.

Transform

The core data structure representing a rigid body transformation:

pub struct Transform<T = Timestamp>
where
    T: TimePoint,
{
    pub translation: Vector3,   // Position offset (x, y, z)
    pub rotation: Quaternion,   // Orientation (w, x, y, z)
    pub timestamp: T,           // When this transform is valid
    pub parent: String,         // Destination frame
    pub child: String,          // Source frame
}

Localized and Transformable Traits

Implement Transformable on your own types to make them transformable, and Localized to enable automatic transform lookup via get_transform_for:

pub trait Localized<T = Timestamp>
where
    T: TimePoint,
{
    fn frame(&self) -> &str;
    fn timestamp(&self) -> T;
}

pub trait Transformable<T = Timestamp>
where
    T: TimePoint,
{
    fn transform(&mut self, transform: &Transform<T>) -> Result<(), TransformError>;
}

The Localized trait provides frame and timestamp introspection, while Transformable handles applying transforms. They are separate so that pure geometry types can implement Transformable without needing frame/timestamp metadata. The library provides a Point type as a reference implementation of both traits.

Usage Examples

Static vs Dynamic Transforms

Static transforms (timestamp = 0) are ideal for fixed relationships like sensor mounts. A given child frame is either static or dynamic: mixing the two kinds for the same child frame is rejected by add_transform with a StaticDynamicConflict error.

The frame tree is strict: a child frame's parent is pinned by its first transform (re-parenting is rejected — remove the frame with Registry::remove_frame and re-add it to change its parent), a frame cannot be its own parent, and cycles are rejected at insertion. Native re-parenting support may become a feature in a later release.

// Static transform: camera mount position (never changes)
let camera_mount = Transform {
    translation: Vector3::new(0.1, 0.0, 0.5),
    rotation: Quaternion::identity(),
    timestamp: Timestamp::zero(),  // Static!
    parent: "base".into(),
    child: "camera".into(),
};

// Dynamic transform: robot position (changes over time)
let robot_position = Transform {
    translation: Vector3::new(x, y, 0.0),
    rotation: Quaternion::identity(),
    timestamp: Timestamp::now(),
    parent: "map".into(),
    child: "base".into(),
};

Transform Chaining

Query transforms between frames that aren't directly connected:

// Add transforms: map -> base -> arm -> gripper
registry.add_transform(map_to_base)?;
registry.add_transform(base_to_arm)?;
registry.add_transform(arm_to_gripper)?;

// Query: map -> gripper (automatically chains through base and arm)
let result = registry.get_transform("map", "gripper", timestamp)?;

The library automatically traverses the frame tree and composes the necessary transforms.

Transform Interpolation

When querying at a timestamp between two stored transforms, the library interpolates:

// Store transforms at t=1 and t=3 (t=0 is reserved as the static sentinel)
registry.add_transform(transform_at_t1)?;
registry.add_transform(transform_at_t3)?;

// Query at t=2: automatically interpolates between t=1 and t=3
let interpolated = registry.get_transform("a", "b", timestamp_at_t2)?;

Translation: Linear interpolation
Rotation: Spherical linear interpolation (SLERP)

Point Transformation

Transform points between coordinate frames using the Transformable trait:

use transforms::{
    geometry::{Point, Quaternion, Transform, Vector3},
    time::Timestamp,
    Transformable,
};

// Create a point in the camera frame
let mut point = Point {
    position: Vector3::new(1.0, 0.0, 0.0),
    orientation: Quaternion::identity(),
    timestamp: Timestamp::now(),
    frame: "camera".into(),
};

// Get the transform that maps camera-frame coordinates into the base frame
let transform = registry.get_transform("base", "camera", point.timestamp)?;

// Transform the point (mutates point.frame to "base")
point.transform(&transform)?;

Transform Into Target Frame

Use get_transform_for to resolve and apply a transform in one step, without manually specifying the source frame or timestamp:

// Create a point in the camera frame
let mut point = Point {
    position: Vector3::new(1.0, 0.0, 0.0),
    orientation: Quaternion::identity(),
    timestamp: Timestamp::now(),
    frame: "camera".into(),
};

// Resolve transform from the point's frame to map, then apply it
let transform = registry.get_transform_for(&point, "map")?;
point.transform(&transform)?;
// point.frame is now "map"

If the point is already in the target frame, an identity transform is returned. This works with any type that implements Localized.

Inverse Transforms

Compute the inverse of a transform:

let base_to_sensor = registry.get_transform("base", "sensor", timestamp)?;
let sensor_to_base = base_to_sensor.inverse()?;

`no_std` Usage

The same API is available in no_std environments, including automatic cleanup via Registry::with_max_age; only a registry built with Registry::new requires manual cleanup:

use transforms::{
    geometry::{Quaternion, Transform, Vector3},
    time::Timestamp,
    Registry,
};
use core::time::Duration;

// Registry::new() has no automatic cleanup; Registry::with_max_age works in
// no_std too if you prefer automatic expiry
let mut registry = Registry::new();

// Create timestamp manually (no Timestamp::now() in no_std)
let timestamp = (Timestamp::zero() + Duration::from_secs(100)).unwrap();

let transform = Transform {
    translation: Vector3::new(1.0, 0.0, 0.0),
    rotation: Quaternion::identity(),
    timestamp,
    parent: "a".into(),
    child: "b".into(),
};

registry.add_transform(transform).unwrap();

// Manual cleanup for registries built without with_max_age
let cutoff = (Timestamp::zero() + Duration::from_secs(50)).unwrap();
registry.delete_transforms_before(cutoff);

Concurrent Access

For multi-threaded applications, wrap the registry in appropriate synchronization primitives:

use std::sync::Arc;
use tokio::sync::Mutex;

let registry = Arc::new(Mutex::new(Registry::with_max_age(Duration::from_secs(60))));

// Writer task
let registry_writer = registry.clone();
tokio::spawn(async move {
    let mut r = registry_writer.lock().await;
    r.add_transform(transform).unwrap();
});

// Reader task
let registry_reader = registry.clone();
tokio::spawn(async move {
    let r = registry_reader.lock().await;
    let result = r.get_transform("a", "b", timestamp);
});

Comparison with ROS2 tf2

This library draws inspiration from ROS2's tf2 (Transform Framework 2), solving the same fundamental problem of coordinate frame tracking. Here's how they compare:

Similarities

Concept	Description
Frame Tree	Both maintain parent-child relationships between coordinate frames
Time Buffering	Both store transforms over time for historical lookups
Interpolation	Both interpolate between transforms for intermediate timestamps
Transform Chaining	Both compute transforms between non-adjacent frames automatically
Static Transforms	Both support transforms that don't change over time

Key Differences

Aspect	ROS2 tf2	transforms
Distribution	Distributed across nodes via DDS	Single-process, local only
Middleware	Tightly coupled to ROS2/DDS	None - completely standalone
Language	C++ with Python/other bindings	Pure Rust
`no_std`	Not supported	Fully supported
Async Pattern	`waitForTransform()` with callbacks	Synchronous (user manages async)
Error Handling	C++ exceptions	Rust `Result` types
Buffer Default	10 seconds	User-configured
Cleanup	Automatic background process	Automatic (`with_max_age`) or manual (`Registry::new`), both modes

Middleware Independence

A core design principle of this library is middleware independence. Unlike tf2, which is deeply integrated with ROS2's DDS-based communication layer, this library has zero middleware dependencies. If you are looking for a crate which drop in integrates with ROS roslibrust_transforms is an option.

This means:

No ROS2 required: Use in any Rust application, not just ROS2 nodes
No DDS overhead: No network traffic, serialization, or distributed consensus
Embedded-friendly: Works in no_std environments with minimal footprint
Bring your own transport: If you need distributed transforms, wrap with your preferred pub-sub system (DDS, MQTT, ZeroMQ, custom protocol, etc.)

This design makes the library suitable for:

Monolithic robotics applications
Embedded systems and microcontrollers
Simulations and testing without ROS2
Applications with custom communication requirements

`TimePoint` vs `Timestamp`

In plain terms:

TimePoint is a trait (an interface). It says what a time type must do so transforms can be stored, compared, and interpolated.
Timestamp is the default struct (a concrete type). It stores time as nanoseconds in a u128.

Use Timestamp if you want the default behavior. Registry::new() is shorthand for Registry::<Timestamp>::new(). If you need a custom clock or custom time representation, implement TimePoint and use Registry::<CustomTimestamp>. With std, std::time::SystemTime support is already implemented, so Registry::<SystemTime> works out of the box.

Performance

O(log n) time lookups: transforms are stored in BTreeMap indexed by timestamp
Early-exit chain resolution: walks stop as soon as the target frame is reached
Automatic cleanup: with_max_age registries prevent unbounded memory growth
Allocation profile: lookups allocate for frame-name bookkeeping and the returned transform (frame names are Strings); insertion into an existing frame does not clone the frame name

Benchmarks are available in the benches/ directory. Run with:

cargo bench

Non-Goals

This library intentionally limits its scope to rigid body transformations (translation and rotation). The following are explicitly not supported:

Scaling transformations
Skew transformations
Perspective transformations
Non-rigid transformations
Affine transformations beyond rigid body motion
API parity with ROS2 tf2
Non-linear interpolation
Extrapolation

This focused scope keeps the library fast, predictable, and specialized for robotics applications. For more general transformation needs, consider a linear algebra or computer graphics library.

Examples

The examples/ directory contains complete working examples:

Example	Description
`std_minimal.rs`	Registry basics: transform a point between frames, with interpolation
`std_full.rs`	Concurrent async usage with Tokio (parallel readers and a writer)
`std_advanced.rs`	Time travel between frames with `get_transform_at`
`no_std_minimal.rs`	Minimal `no_std` usage: add and retrieve a transform
`no_std_full.rs`	Point transform and interpolation with manual cleanup
`no_std_advanced.rs`	Time travel in `no_std` with manual cleanup

Run examples with:

cargo run --example std_full
cargo run --example no_std_minimal --no-default-features

AI-Assisted Development

Parts of this library have been developed with AI assistance (Claude Code), including some work that predates v2.0.0. Starting with v2.0.0, AI-assisted contributions follow a formal framework:

Every AI-assisted commit is disclosed with an Assisted-by: commit trailer (following the Linux kernel convention, e.g. Assisted-by: Claude:claude-fable-5), making AI involvement machine-queryable from v2.0.0 onward:
```
git log --grep="Assisted-by:"
```
The standards, invariants, and conventions that AI agents must follow when working on this repository are documented in AGENTS.md.
Every AI-assisted change is reviewed, tested, and understood by the maintainer before merging.

I, the owner of this repo, take full responsibility for every line in this repository, however it was produced.

Contributing

Contributions are welcome! Please feel free to submit issues, feature requests, or pull requests.

This applies to contributors as well as the maintainer: AI-assisted contributions must follow the standards in AGENTS.md and carry the Assisted-by: commit trailer described above.

License

This project is licensed under the MIT License - see the LICENSE file for details.

transforms 2.0.0-beta.4

Transforms

Overview

Features

What's New

v2.0.0 highlights

Installation

Feature Flags

Quick Start

API Reference

Registry

Core Types

Architecture

Registry

Buffer

Transform

Localized and Transformable Traits

Usage Examples

Static vs Dynamic Transforms

Transform Chaining

Transform Interpolation

Point Transformation

Transform Into Target Frame

Inverse Transforms

no_std Usage

Concurrent Access

Comparison with ROS2 tf2

Similarities

Key Differences

Middleware Independence

TimePoint vs Timestamp

Performance

Non-Goals

Examples

AI-Assisted Development

Contributing

License

`no_std` Usage

`TimePoint` vs `Timestamp`