HRoPE: Homography Relative Positional Encoding

Hugging Face Daily Papers Papers

Summary

HRoPE introduces a surface-aware positional encoding that models each patch as a slanted 3D plane and injects plane-induced homographies as relative transformations into attention, improving cross-view alignment and novel view synthesis without ground-truth geometry. Experiments on RealEstate10K, CO3Dv2, and DL3DV show it outperforms existing geometric positional encodings.

Geometric Relative Positional Encoding has become the primary mechanism for injecting spatial inductive biases into multi-view transformers. Existing designs condition attention on camera-level frustums or ray-marched depth, associating cross-view tokens through the sensor geometry. Such sensor-centric formulations, however, describe only where a token is observed from, leaving the rich surface geometry of the scene region depicted by the token. In this paper, we advocate a shift toward surface-aware positional encoding that explicitly grounds patch tokens in the geometry of physical surfaces. We introduce HRoPE, which represents the local geometry of each patch as a slanted 3D plane, following the slanted support-window assumption of classical multi-view stereo. We inject token-level, plane-induced homographies into attention as relative transformations. This equips the transformer with a geometric prior for rectifying perspective distortions and aligning patch features across viewpoints. Our encoding requires no ground-truth geometry: the plane parameters can be predicted end-to-end under a view-synthesis objective alone, or derived from foundation models. Extensive experiments on RealEstate10K, CO3Dv2, and DL3DV show that our best variant of HRoPE consistently outperforms the evaluated geometric positional encodings for novel view synthesis. Extensive ablations and analysis show the effectiveness of the proposed encoding. Please refer to our project page at: https://gaohchen.github.io/HRoPE
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Source: https://huggingface.co/papers/2610.28284

Abstract

HRoPE introduces surface-aware positional encoding using slanted 3D planes and homographies to improve cross-view alignment and novel view synthesis without requiring ground-truth geometry.

Geometric Relative Positional Encodinghas become the primary mechanism for injecting spatial inductive biases intomulti-view transformers. Existing designs condition attention on camera-level frustums or ray-marched depth, associatingcross-view tokensthrough the sensor geometry. Such sensor-centric formulations, however, describe only where a token is observed from, leaving the rich surface geometry of the scene region depicted by the token. In this paper, we advocate a shift toward surface-aware positional encoding that explicitly grounds patch tokens in the geometry of physical surfaces. We introduceHRoPE, which represents the local geometry of each patch as aslanted 3D plane, following the slanted support-window assumption of classical multi-view stereo. We inject token-level,plane-induced homographiesinto attention asrelative transformations. This equips the transformer with a geometric prior for rectifying perspective distortions and aligning patch features across viewpoints. Our encoding requires no ground-truth geometry: the plane parameters can be predicted end-to-end under a view-synthesis objective alone, or derived from foundation models. Extensive experiments on RealEstate10K, CO3Dv2, and DL3DV show that our best variant ofHRoPEconsistently outperforms the evaluated geometric positional encodings fornovel view synthesis. Extensive ablations and analysis show the effectiveness of the proposed encoding. Please refer to our project page at: https://gaohchen.github.io/HRoPE

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