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Point cloud semantic segmentation via Deep 3D Convolutional Neural Network

This code implements a deep neural network for 3D point cloud semantic segmentation. It comes as a baseline for the benchmark http://www.semantic3d.net/ (reproduces DeepNet entry in reduced-8 track). It is written in C++/lua and is supposed to simplify starting to work with the benchmark.

The code requires at least 8 Gb RAM and an Nvidia GPU (at least 6 Gb of memory, tested for Nvidia Titan X GPU).

If you use this code or the benchmark in your research, please cite it as

@article{hackel2017semantic3d,
title={Semantic3D.net: A new Large-scale Point Cloud Classification Benchmark},
author={Hackel, Timo and Savinov, Nikolay and Ladicky, Lubor and Wegner, Jan and Schindler, Konrad and Pollefeys, Marc},
journal={arXiv preprint arXiv:1704.03847},
year={2017}
}

How does it work

Each point in the point cloud is to be classified into one of the semantic classes like building/car/vegetation/etc. It is done by considering a range of neighbourhoods for the point, computing occupancy grids for them and applying 3D convolutional neural network on those grids. A more detailed description can be found in this presentation.

Instructions for Linux (tested for Ubuntu 16.04.2 LTS):

  1. install torch (tested for commit 5c1d3cfda8101123628a45e70435d545ae1bc771 from June 7, 2017), cuda (tested for v8.0) and cudnn (tested for v5.1). For the latter, follow the instructions https://github.com/soumith/cudnn.torch
  2. clone this repository
  3. run "cd build; ./setup.sh" to download data and transform it into necessary format.
  4. run "./build_run.sh" to prepare small train/validation sets to track optimization progress
  5. run "cd ../src; ./launch_training.sh". You can track the progress in nohup.out file. Wait until the train error becomes close to 0 and test error start to oscillate around some value. Then kill the process (took 304 epochs for the baseline).
  6. run "./launch_prediction.sh". You might want to change gpu indexes in this script depending on number of gpus you have available. You can also tweak number of openmp threads. Wait until it finishes (might take a day or so).
  7. after prediction finishes, run "./prepare_to_submit.sh" to put the submission into necessary format.
  8. submit data/benchmark/submit.zip to the server http://www.semantic3d.net/submit_public.php.

Parameters

The changeable constants are in lib/point_cloud_util/data_loader_constants.h and in src/point_cloud_constants.lua

Explanation of them:

lib/point_cloud_util/data_loader_constants.h:

const int kWindowSize = 16; // neighbourhood of the point is voxelized into kWindowSize ^ 3 voxels

const int kBatchSize = 100; // since batch is constructed on cpp side, we need specify its size here

const int kNumberOfClasses = 8; // integer labels 1, ..., 8 are considered

const int kDefaultNumberOfScales = 5; // each sample in the batch is constructed as stacked multiples scales. in the deep net architecture fully connected layer outputs are concatenated

const int kDefaultNumberOfRotations = 1; // optional implemenation of TI-pooling on top of multi-scale architecture. check the repository or read the paper for more details

const float kSpatialResolution = 0.025; // voxel side in meters

const int kBatchResamplingLimit = 100; // after this number of batches, the coordinate system is rotated by a random angle and the voxelized representations are recalculated from scratch (augmentation).

src/point_cloud_constants.lua:

opt.number_of_filters = 16 -- number of filters in the first convolutional layer, other layers size is also proportional to this constant.

opt.kLargePrintingInterval = 100 -- how often to evaluate model and dump solution to disk

opt.kWarmStart = false -- restart with the saved model

opt.kModelDumpName = '../dump/model_dump' -- where the model is saved

opt.kOptimStateDumpName = '../dump/optim_state_dump' -- where the optimization progress is saved

opt.kStreamingPath = '../data/benchmark/sg28_station4_intensity_rgb_train.txt' -- from which file training data is sampled

Caveats

Data is randomly sampled from the training set, all the classes are made equally probable via this sampling. Thus it is required that the training file contains at least one sample of each class.

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Point cloud semantic segmentation via Deep 3D Convolutional Neural Network

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