upal

UPAL: Unified and Efficient Point-Line Local Features (ECCV 2026)

Joint keypoint + line local feature extractor. One forward pass predicts sub-pixel keypoints with confidence scores, 128-D L2-normalised descriptors, a dense keypoint/junction heatmap and a dense line distance field. Line segments are obtained by seeding a modified LSD detector with the learned keypoints and filtering its proposals with the distance field.

• Paper: arXiv 2608.19894
• Code: github.com/francois141/upal
• Authors: François Costa*, Raphael Kreft*, Eckhard Goedeke, Felix Möller, Hardik Shah, Ramanathan Rajaraman, Shaohui Liu, Rémi Pautrat, Marc Pollefeys (* equal contribution)

Red: learned keypoints · green: line segments supported by the learned distance field · coloured links: mutual-nearest descriptor matches.

Installation

pip install upal   # network + point-seeded line detector

Usage

import cv2
import torch
from upal import UPAL, mutual_nearest_neighbors, match_lines_from_endpoints

model = UPAL.from_pretrained("rkreft/upal").to("cuda" if torch.cuda.is_available() else "cpu")

def read(path):
    image = cv2.cvtColor(cv2.imread(path), cv2.COLOR_BGR2RGB)
    return torch.from_numpy(image).permute(2, 0, 1).float() / 255.0

feats0, feats1 = model.extract(read("img0.png")), model.extract(read("img1.png"))
feats0["keypoints"]            # N x 2 pixel (x, y)
feats0["descriptors"]          # N x 128, L2-normalised
feats0["keypoint_scores"]      # N
feats0["keypoint_dispersity"]  # N, spread of the score peak (lower = sharper)
feats0["keypoint_heatmap"]     # H x W
feats0["line_distance_field"]  # H x W, distance to the nearest line in pixels
feats0["lines"]                # L x 2 x 2 endpoints

# Point matching: mutual nearest neighbours on descriptors.
point_matches = mutual_nearest_neighbors(feats0["descriptors"], feats1["descriptors"])  # M x 2 indices

# Line matching: describe both endpoints of each segment, then solve a one-to-one assignment.
desc0 = model.describe_lines(read("img0.png"), feats0["lines"])  # L0 x 2 x 128
desc1 = model.describe_lines(read("img1.png"), feats1["lines"])  # L1 x 2 x 128
line_matches, scores = match_lines_from_endpoints(desc0, desc1)   # K x 2 indices, K scores (NumPy)

To skip line post-processing, call model.extract(image, lines=False); lines is then empty (0 x 2 x 2) and everything else is unchanged.

extract(image, lines=True, max_lines=200, min_line_length=25.0, max_line_distance=2.0) takes a C x H x W tensor in [0, 1] (RGB or grayscale); the number of keypoints is set by UPAL.from_pretrained("rkreft/upal", max_num_keypoints=2048). Images are padded to a multiple of 32 internally and outputs are returned in input-image coordinates.

Model details

• Encoder: ALIKED-style four-level encoder (16/32/64/128 channels) with deformable convolutions in the two deepest stages, fused to a 128-channel full-resolution feature map.
• Heads: keypoint/junction score head; sparse deformable descriptor head (SDDH, 16 samples, 128-D); line distance-field decoder (values in [0, 5] px).
• Post-processing: NMS (radius 3) with differentiable sub-pixel refinement; keypoint-seeded LSD (points-lsd) filtered by the mean distance-field value along the segment; mutual-nearest-neighbour point matching; endpoint-descriptor line matching with a maximum-weight assignment.
• Weights: this repository holds the inference subset of the trained checkpoint (model.safetensors, 0.79M parameters, 3.2 MB) and its configuration (config.json).
• Training: distilled from SuperPoint, ALIKED, DaD and DeepLSD teachers; see the paper for datasets, losses and evaluation.

Files

License

Apache-2.0 (weights and code). Line detection uses points-lsd, whose LSD core is AGPL-3.0-or-later.

Citation

@misc{costa2026unifiedefficientpointlinelocal,
  title={Unified and Efficient Point-Line Local Features},
  author={François Costa and Raphael Kreft and Eckhard Goedeke and Felix Möller and Hardik Shah and Ramanathan Rajaraman and Shaohui Liu and Rémi Pautrat and Marc Pollefeys},
  year={2026},
  eprint={2608.19894},
  archivePrefix={arXiv},
  primaryClass={cs.CV},
  url={https://arxiv.org/abs/2608.19894},
}

Acknowledgements

Parts of the code reuse ALIKED and glue-factory. We thank the authors of SuperPoint, ALIKED, DaD and DeepLSD for releasing the pre-trained models used as teachers.