SpConv: PyTorch Spatially Sparse Convolution Library

This is a spatially sparse convolution library like SparseConvNet but faster and easy to read. This library provide sparse convolution/transposed, submanifold convolution, inverse convolution and sparse maxpool.

If you need more kinds of spatial layers such as avg pool, please implement it by yourself, I don't have time to do this.

The GPU Indice Generation algorithm is a unofficial implementation of paper SECOND. That algorithm (don't include GPU SubM indice generation algorithm) may be protected by patent.

This project only support CUDA 9.0+. If you are using cuda 8.0, please update it to 9.0.

Install

Use git clone xxx.git --recursive to clone this repo.
Install boost headers to your system include path, you can use either sudo apt-get install libboostall-dev or download compressed files from boost official website and copy headers to include path.
Download cmake >= 3.13.2, then add cmake executables to PATH.
Ensure you have install pytorch 1.0 in your environment, run python setup.py bdist_wheel (don't use python setup.py install).
Run cd ./dist, use pip to install generated whl file.

Compare with SparseConvNet

Features

SparseConvNet's Sparse Convolution don't support padding and dilation, spconv support this.
spconv only contains sparse convolutions, the batchnorm and activations can directly use layers from torch.nn, SparseConvNet contains lots of their own implementation of layers such as batchnorm and activations.

Speed

spconv is faster than SparseConvNet due to gpu indice generation and gather-gemm-scatter algorithm. SparseConvNet use hand-written gemm which is slow.

Usage

SparseConvTensor

features = # your features with shape [N, numPlanes]
indices = # your indices/coordinates with shape [N, ndim + 1], batch index must be put in indices[:, 0]
spatial_shape = # spatial shape of your sparse tensor.
batch_size = # batch size of your sparse tensor.
x = spconv.SparseConvTensor(features, indices, spatial_shape, batch_size)
x_dense_NCHW = x.dense() # convert sparse tensor to dense NCHW tensor.
print(x.sparity) # helper function to check sparity.

Sparse Convolution

import spconv
from torch import nn
class ExampleNet(nn.Module):
    def __init__(self, shape):
        super().__init__()
        self.net = spconv.SparseSequential(
            spconv.SparseConv3d(32, 64, 3), # just like nn.Conv3d but don't support group and all([d > 1, s > 1])
            nn.BatchNorm1d(64), # non-spatial layers can be used directly in SparseSequential.
            nn.ReLU(),
            spconv.SubMConv3d(64, 64, 3, indice_key="subm0"),
            nn.BatchNorm1d(64),
            nn.ReLU(),
            # when use submanifold convolutions, their indices can be shared to save indices generation time.
            spconv.SubMConv3d(64, 64, 3, indice_key="subm0"),
            nn.BatchNorm1d(64),
            nn.ReLU(),
            spconv.SparseConvTranspose3d(64, 64, 3, 2),
            nn.BatchNorm1d(64),
            nn.ReLU(),
            spconv.ToDense(), # convert spconv tensor to dense and convert it to NCHW format.
            nn.Conv3d(64, 64, 3),
            nn.BatchNorm1d(64),
            nn.ReLU(),
        )
        self.shape = shape

    def forward(self, features, coors, batch_size):
        coors = coors.int() # unlike torch, this library only accept int coordinates.
        x = spconv.SparseConvTensor(features, coors, self.shape, batch_size)
        return self.net(x)# .dense()

Inverse Convolution

Inverse sparse convolution means "inv" of sparse convolution. the output of inverse convolution contains same indices as input of sparse convolution.

Inverse convolution usually used in semantic segmentation.

class ExampleNet(nn.Module):
    def __init__(self, shape):
        super().__init__()
        self.net = spconv.SparseSequential(
            spconv.SparseConv3d(32, 64, 3, 2, indice_key="cp0"),
            spconv.SparseInverseConv3d(64, 32, 3, indice_key="cp0"), # need provide kernel size to create weight
        )
        self.shape = shape

    def forward(self, features, coors, batch_size):
        coors = coors.int()
        x = spconv.SparseConvTensor(features, coors, self.shape, batch_size)
        return self.net(x)

Utility functions

convert point cloud to voxel

voxel_generator = spconv.utils.VoxelGenerator(
    voxel_size=[0.1, 0.1, 0.1], 
    point_cloud_range=[-50, -50, -3, 50, 50, 1],
    max_num_points=30,
    max_voxels=40000
)

points = # [N, 3+] tensor.
voxels, coords, num_points_per_voxel = voxel_generator.generate(points)

Implementation Details

This implementation use gather-gemm-scatter framework to do sparse convolution.

Projects using spconv:

second.pytorch: Point Cloud Object Detection in KITTI Dataset.

Authors

Yan Yan - Initial work - traveller59
Bo Li - gpu indice generation idea, owner of patent of the sparse conv gpu indice generation algorithm (don't include subm) - prclibo

License

This project is licensed under the Apache license 2.0 License - see the LICENSE.md file for details

llijiang/spconv