Smooth sampler

A drop-in replacement for Pytorch's grid_sample supporting smoothstep activation for interpolation weights (proposed in Instant NGP by Müller et al.) as well as double backpropagation. Currently supports 3D inputs and trilinear interpolation mode. Based on Pytorch's native grid_sampler code. Used in GO-Surf by Wang et al.

Installation

On Python3 environment with Pytorch >=1.11 CUDA installation run:

pip install git+https://github.com/tymoteuszb/smooth-sampler

Usage

The API is consistent with Pytorch's grid_sample:

import torch
from smooth_sampler import SmoothSampler

align_corners = True
padding_mode = "zeros"

input = (torch.rand([2,2,2,3,11], device="cuda")).requires_grad_(True)
grid = (torch.rand([2,2,1,5,3], device="cuda") * 2. - 1.).requires_grad_(True)

out1 = SmoothSampler.apply(input, grid, padding_mode, align_corners, False)
out2 = torch.nn.functional.grid_sample(input, grid, padding_mode=padding_mode, align_corners=align_corners)
assert torch.allclose(out1, out2)

grad1_input, grad1_grid = torch.autograd.grad(out1, [input, grid], torch.ones_like(out1), create_graph=True)
grad2_input, grad2_grid = torch.autograd.grad(out2, [input, grid], torch.ones_like(out2), create_graph=True)
assert torch.allclose(grad1_input, grad2_input)
assert torch.allclose(grad1_grid, grad2_grid)

loss1 = out1.sum() + grad1_input.sum() + grad1_grid.sum()
loss1.backward() # Works!

loss2 = out2.sum() + grad2_input.sum() + grad2_grid.sum()
loss2.backward() # RuntimeException: derivative for aten::grid_sampler_3d_backward is not implemented

Citation

If you use this code in your project, please consider adding a citation:

@article{wang2022go-surf,
  title={GO-Surf: Neural Feature Grid Optimization for Fast, High-Fidelity RGB-D Surface Reconstruction},
  author={Wang, Jingwen and Bleja, Tymoteusz and Agapito, Lourdes},
  journal={arXiv preprint},
  year={2022}
}