PointNet Classification

Classification of PointCloud structure using PointNet model


For visualization purpose we will require to install Makie and compatible backend (GLMakie or WGLMakie). To install it simply run ] add Makie in the julia prompt.

using Flux3D, Flux, Makie, CUDA
using Flux: onehotbatch, onecold, onehot, crossentropy
using Statistics: mean
using Base.Iterators: partition

Makie.set_theme!(show_axis = false)

Defining arguments for use in training.

  • batch_size - batch size of of training data to be passed while training.
  • lr - learing rate for the optimization.
  • epochs - number of episodes for training the classification model.
  • num_classes - number of classes in labels of dataset.
  • npoints - number of points in each PointCloud to be returned by dataset.
batch_size = 32
lr = 3e-4
epochs = 5
num_classes = 10 #possible values {10,40}
npoints = 1024

ModelNet10 Dataset

This package has dataset wrapper for ModelNet10/40 which makes it easy to load and preprocess ModelNet dataset. In this example we will using ModelNet10 but we can also use ModelNet40 with minor tweak in num_classes args.

We can construct ModelNet10 dataset by passing:

  • mode=:pointcloud - for returning PointCloud variant of dataset
  • npoints - no. of points in each PointCloud.
  • transforms - Transforms to be applied before return specified PointCloud.
  • train - Bool to indicate training or testing split.

Detailed list of available arguments can be found in ModelNet section.

dset = ModelNet10.dataset(;
    mode = :pointcloud,
    npoints = npoints,
    transform = NormalizePointCloud(),
val_dset = ModelNet10.dataset(;
    mode = :pointcloud,
    train = false,
    npoints = npoints,
    transform = NormalizePointCloud(),

Visualizing the dataset

we can access the dataset by correspond index like dset[1] which will return a ModelNet10 DataPoint and following information idx: 1, data: PointCloud{Float32}, ground_truth: 1 (bathtub).

For the visulizing the corresponding datapoint we can use visulize

visualize(dset[11], markersize = 0.1)

Preparing Dataloader for training.

data = [dset[i].data.points for i = 1:length(dset)]
labels =
    onehotbatch([dset[i].ground_truth for i = 1:length(dset)], 1:num_classes)

valX = cat([val_dset[i].data.points for i = 1:length(val_dset)]..., dims = 3)
valY = onehotbatch(
    [val_dset[i].ground_truth for i = 1:length(val_dset)],

    (cat(data[i]..., dims = 3), labels[:, i])
    for i in partition(1:length(data), batch_size)
VAL = (valX, valY)

Defining 3D model

Flux3D has predefined PointNet classification model which can be used to train PointCloud dataset

m = PointNet(num_classes)

Defining loss and validating objectives

loss(x, y) = crossentropy(m(x), y)
accuracy(x, y) =
    mean(onecold(cpu(m(x)), 1:num_classes) .== onecold(cpu(y), 1:num_classes))

Defining learning rate and optimizer

opt = Flux.ADAM(lr)

Using GPU for fast training [Optional]

We can convert the 3D model to GPU or CPU usinggpu and cpu, and also changing the dataloader using same function

m = m |> gpu
TRAIN = TRAIN |> gpu
VAL = VAL |> gpu

Training the 3D model

ps = params(m)
for epoch = 1:epochs
    running_loss = 0
    for d in TRAIN
        gs = gradient(ps) do
            training_loss = loss(d...)
            running_loss += training_loss
            return training_loss
        Flux.update!(opt, ps, gs)
    print("Epoch: $(epoch), epoch_loss: $(running_loss), accuracy: $(accuracy(VAL...))\n")
@show accuracy(VAL...)

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