This is a CPU-only fork of Zachary Teed's wonderful LieTorch Library. It's intended for use as classroom instructional materials, and students are not expected to have GPU-enabled machines.
The LieTorch library generalizes PyTorch to 3D transformation groups. Just as torch.Tensor
is a multi-dimensional matrix of scalar elements, lietorch.SE3
is a multi-dimensional matrix of SE3 elements. We support common tensor manipulations such as indexing, reshaping, and broadcasting. Group operations can be composed into computation graphs and backpropagation is automatically peformed in the tangent space of each element. For more details, please see our paper:
Tangent Space Backpropagation for 3D Transformation Groups Zachary Teed and Jia Deng, CVPR 2021
@inproceedings{teed2021tangent,
title={Tangent Space Backpropagation for 3D Transformation Groups},
author={Teed, Zachary and Deng, Jia},
booktitle={Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR)},
year={2021},
}
pip install git+https://github.com/w-hc/lietorch
- PyTorch >= 1.8
To run the examples, you will need OpenCV and Open3D. Depending on your operating system, OpenCV and Open3D can either be installed with pip or may need to be built from source
pip install opencv-python open3d
LieTorch currently supports the 3D transformation groups.
Group | Dimension | Action |
---|---|---|
SO3 | 3 | rotation |
RxSO3 | 4 | rotation + scaling |
SE3 | 6 | rotation + translation |
Sim3 | 7 | rotation + translation + scaling |
Each group supports the following differentiable operations:
Operation | Map | Description |
---|---|---|
exp | g -> G | exponential map |
log | G -> g | logarithm map |
inv | G -> G | group inverse |
mul | G x G -> G | group multiplication |
adj | G x g -> g | adjoint |
adjT | G x g*-> g* | dual adjoint |
act | G x R^3 -> R^3 | action on point (set) |
act4 | G x P^3 -> P^3 | action on homogeneous point (set) |
matrix | G -> R^{4x4} | convert to 4x4 matrix |
vec | G -> R^D | map to Euclidean embedding vector |
InitFromVec | R^D -> G | initialize group from Euclidean embedding |
Compute the angles between all pairs of rotation matrices
import torch
from lietorch import SO3
phi = torch.randn(8000, 3, device='cuda', requires_grad=True)
R = SO3.exp(phi)
# relative rotation matrix, SO3 ^ {8000 x 8000}
dR = R[:,None].inv() * R[None,:]
# 8000x8000 matrix of angles
ang = dR.log().norm(dim=-1)
# backpropogation in tangent space
loss = ang.sum()
loss.backward()
We provide differentiable FromVec
and ToVec
functions which can be used to convert between LieGroup elements and their vector embeddings. Additional, the .matrix
function returns a 4x4 transformation matrix.
# random quaternion
q = torch.randn(1, 4, requires_grad=True)
q = q / q.norm(dim=-1, keepdim=True)
# create SO3 object from quaternion (differentiable w.r.t q)
R = SO3.InitFromVec(q)
# 4x4 transformation matrix (differentiable w.r.t R)
T = R.matrix()
# map back to quaterion (differentiable w.r.t R)
q = R.vec()
We provide real use cases in the examples directory
- Pose Graph Optimization
- Deep SE3/Sim3 Registrtion
- RGB-D SLAM / VO
Many of the Lie Group implementations are adapted from Sophus.