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Licensed under the MIT License.

Pretrained Weights

In this tutorial, we demonstrate some available pretrained weights in TorchGeo. The implementation follows torchvisions’ recently introduced Multi-Weight API. We will use the EuroSAT dataset throughout this tutorial. Specifically, a subset containing only 100 images.

It’s recommended to run this notebook on Google Colab if you don’t have your own GPU. Click the “Open in Colab” button above to get started.

Setup

First, we install TorchGeo.

%pip install torchgeo

Imports

Next, we import TorchGeo and any other libraries we need.

%matplotlib inline

import os
import tempfile

import timm
import torch
from lightning.pytorch import Trainer

from torchgeo.datamodules import EuroSAT100DataModule
from torchgeo.trainers import ClassificationTask
from torchgeo.models import ResNet18_Weights

The following variables can be used to control training.

batch_size = 10
num_workers = 2
max_epochs = 10
fast_dev_run = False

Datamodule

We will utilize TorchGeo’s Lightning datamodules to organize the dataloader setup.

root = os.path.join(tempfile.gettempdir(), "eurosat100")
datamodule = EuroSAT100DataModule(
    root=root, batch_size=batch_size, num_workers=num_workers, download=True
)

Weights

Available pretrained weights are listed on the model documentation page. While some weights only accept RGB channel input, some weights have been pretrained on Sentinel 2 imagery with 13 input channels and can hence prove useful for transfer learning tasks involving Sentinel 2 data.

To access these weights you can do the following:

weights = ResNet18_Weights.SENTINEL2_ALL_MOCO

This set of weights is a torchvision WeightEnum and holds information such as the download url link or additional meta data. TorchGeo takes care of the downloading and initialization of models with a desired set of weights. Given that EuroSAT is a classification dataset, we can use a ClassificationTask object that holds the model and optimizer object as well as the training logic.

task = ClassificationTask(
    model="resnet18",
    loss="ce",
    weights=weights,
    in_channels=13,
    num_classes=10,
    lr=0.001,
    patience=5,
)

If you do not want to utilize the ClassificationTask functionality for your experiments, you can also just create a timm model with pretrained weights from TorchGeo as follows:

in_chans = weights.meta["in_chans"]
model = timm.create_model("resnet18", in_chans=in_chans, num_classes=10)
model = model.load_state_dict(weights.get_state_dict(progress=True), strict=False)

Training

To train our pretrained model on the EuroSAT dataset we will make use of Lightning’s Trainer. For a more elaborate explanation of how TorchGeo uses Lightning, check out this tutorial.

accelerator = "gpu" if torch.cuda.is_available() else "cpu"
default_root_dir = os.path.join(tempfile.gettempdir(), "experiments")

trainer = Trainer(
    accelerator=accelerator,
    default_root_dir=default_root_dir,
    fast_dev_run=fast_dev_run,
    log_every_n_steps=1,
    min_epochs=1,
    max_epochs=max_epochs,
)

trainer.fit(model=task, datamodule=datamodule)