Coarse LoFTR TRT

Google Colab demo notebook

This project provides a deep learning model for the Local Feature Matching for two images that can be used on the embedded devices like NVidia Jetson Nano 2GB with a reasonable accuracy and performance - 5 FPS. The algorithm is based on the coarse part of “LoFTR: Detector-Free Local Feature Matching with Transformers”. But the model has a reduced number of ResNet and coarse transformer layers so there is the much lower memory consumption and the better performance. The required level of accuracy was achieved by applying the Knowledge distillation technique and training on the BlendedMVS dataset.

The code is based on the original LoFTR repository, but was adapted for compatibility with TensorRT technology, especially dependencies to einsum and einops were removed.

Model weights

Weights for the PyTorch model, ONNX model and TensorRT engine files are located in the weights folder.

Weights for original LoFTR coarse module can be downloaded using the original url that was provider by paper authors, now only the outdoor-ds file is supported.

Demo

There is a Demo application, that can be ran with the webcam.py script. There are following parameters:

• --weights - The path to PyTorch model weights, for example ‘weights/LoFTR_teacher.pt’ or ‘weights/outdoor_ds.ckpt’
• --trt - The path to the TensorRT engine, for example ‘weights/LoFTR_teacher.trt’
• --onnx - The path to the ONNX model, for example ‘weights/LoFTR_teacher.onnx’
• --original - If specified the original LoFTR model will be used, can be used only with --weights parameter
• --camid - OpenCV webcam video capture ID, usually 0 or 1, default 0
• --device - Selects the runtime back-end CPU or CUDA, default is CUDA

Sample command line:

python3 webcam.py --trt=weights/LoFTR_teacher.trt --camid=0

Demo application shows a window with pair of images captured with a camera. Initially there will be the two same images. Then you can choose a view of interest and press the s button, the view will be remembered and will be visible as the left image. Then you can change the view and press the p button to make a snapshot of the feature matching result, the corresponding features will be marked with the same numbers at the two images. If you press the p button again then application will allow you to change the view and repeat the feature matching process. Also this application shows the real-time FPS counter so you can estimate the model performance.

Training

To repeat the training procedure you should use the low-res set of the BlendedMVS dataset. After download you can use the train.py script to run training process. There are following parameters for this script:

• --path - Path to the dataset
• --checkpoint_path - Where to store a log information and checkpoints, default value is ‘weights’
• --weights - Path to the LoFTR teacher model weights, default value is ‘weights/outdoor_ds.ckpt’

Sample command line:

python3 train.py --path=/home/user/datasets/BlendedMVS --checkpoint_path=weights/experiment1/

Please use the train/settings.py script to configure the training process. Please notice that by default the following parameters are enabled:

self.batch_size = 32
self.batch_size_divider = 8  # Used for gradient accumulation
self.use_amp = True
self.epochs = 35
self.epoch_size = 5000

This set of parameters was chosen for training with the Nvidia GTX1060 GPU, which is the low level consumer level card. The use_amp parameter means the automatic mixed precision will be used to reduce the memory consumption and the training time. Also, the gradient accumulation technique is enabled with the batch_size_divider parameter, it means the actual batch size will be 32/8 but for larger batch size simulation the 8 batches will be averaged. Moreover, the actual size of the epoch is reduced with the epoch_size parameter, it means that on every epoch only 5000 dataset elements will be randomly picked from the whole dataset.

Paper

@misc{kolodiazhnyi2022local,
      title={Local Feature Matching with Transformers for low-end devices}, 
      author={Kyrylo Kolodiazhnyi},
      year={2022},
      eprint={2202.00770},
      archivePrefix={arXiv},
      primaryClass={cs.CV}
}

LoFTR Paper:

@article{sun2021loftr,
  title={{LoFTR}: Detector-Free Local Feature Matching with Transformers},
  author={Sun, Jiaming and Shen, Zehong and Wang, Yuang and Bao, Hujun and Zhou, Xiaowei},
  journal={{CVPR}},
  year={2021}
}