Scal3R: Learning Efficient Multi-Relative Pose Query for Scalable Online 3D Reconstruction

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Summary

Scal3R improves online 3D reconstruction for long videos by using multi-reference relative pose querying with lightweight tokens and pose-graph optimization, reducing drift and achieving state-of-the-art performance.

Online 3D reconstruction models perform poorly on long videos. This happens because regressing poses relative to a fixed first-frame anchor forces extrapolation far beyond the training distribution. Small drifts accumulate and amplify into significant geometric collapse. However, we observe that per-frame depth remains stable throughout this failure. The backbone's local geometry remains intact; only the global pose head breaks down. Motivated by this decoupling, we introduce Scal3R. This approach reformulates online reconstruction as multi-reference relative pose querying. We use lightweight learnable tokens, which make up about ~1% of the parameters, and inject them into a completely frozen backbone via asymmetric attention. This setup queries poses relative to multiple past keyframes. An online pose-graph optimization system with loop closure suppresses long-range drift. Scal3R reaches convergence in 8 hours on a single GPU. It reduces the average ATE by over 60% on KITTI compared to the online baseline. It also achieves state-of-the-art performance across Virtual KITTI, Sintel, TUM-Dynamic, ScanNet, and 7-Scenes. Project page: https://linjohnss.github.io/scal3r/
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Paper page - Scal3R: Learning Efficient Multi-Relative Pose Query for Scalable Online 3D Reconstruction

Source: https://huggingface.co/papers/2609.04201

Abstract

Scal3R improves long-video online 3D reconstruction by querying multi-reference relative poses with lightweight tokens and pose-graph optimization, reducing drift without retraining the backbone.

Online 3D reconstructionmodels perform poorly on long videos. This happens because regressing poses relative to a fixed first-frame anchor forces extrapolation far beyond the training distribution. Small drifts accumulateand amplify into significant geometric collapse. However, we observe that per-frame depth remains stable throughout this failure. The backbone’s local geometry remains intact; only the global pose head breaks down. Motivated by this decoupling, we introduce Scal3R. This approach reformulates online reconstruction as multi-referencerelative pose querying. We use lightweightlearnable tokens, which make up about ~1% of the parameters, and inject them into a completelyfrozen backboneviaasymmetric attention. This setup queries poses relative to multiple past keyframes. An onlinepose-graph optimizationsystem withloop closuresuppresses long-range drift. Scal3R reaches convergence in 8 hours on a single GPU. It reduces the averageATEby over 60% on KITTI compared to the online baseline. It also achieves state-of-the-art performance across Virtual KITTI, Sintel, TUM-Dynamic, ScanNet, and 7-Scenes. Project page: https://linjohnss.github.io/scal3r/

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