ESCAPE: Equivariant Shape Completion via Anchor Point Encoding
Burak Bekci, Nassir Navab, Federico Tombari, Mahdi Saleh

TL;DR
ESCAPE introduces a rotation-equivariant shape completion framework using anchor point encoding and transformers, enabling accurate 3D shape reconstruction under arbitrary rotations without pose estimation.
Contribution
The paper proposes a novel anchor point encoding strategy combined with transformers to achieve rotation-equivariant shape completion, improving robustness to orientation variations.
Findings
Achieves high-quality shape reconstructions under arbitrary rotations.
Outperforms existing methods in robustness and accuracy.
Operates effectively without pose estimation modules.
Abstract
Shape completion, a crucial task in 3D computer vision, involves predicting and filling the missing regions of scanned or partially observed objects. Current methods expect known pose or canonical coordinates and do not perform well under varying rotations, limiting their real-world applicability. We introduce ESCAPE (Equivariant Shape Completion via Anchor Point Encoding), a novel framework designed to achieve rotation-equivariant shape completion. Our approach employs a distinctive encoding strategy by selecting anchor points from a shape and representing all points as a distance to all anchor points. This enables the model to capture a consistent, rotation-equivariant understanding of the object's geometry. ESCAPE leverages a transformer architecture to encode and decode the distance transformations, ensuring that generated shape completions remain accurate and equivariant under…
Peer Reviews
Decision·ICLR 2025 Conference Withdrawn Submission
**Significance**: 1. Point cloud completion is a significant task with extended literature. 2. The authors show cases where the shape completion is better than some compared methods. **Novelty**: 1. **High curvature anchor point selection**: The authors's approach to select the anchor points is novel to my knowledge. 2. **Distance Representation**: The reduction of absolute coordinates to distances w.r.t. invariantly selected anchor points is novel to my knowledge. **Clarity**: The paper
**Significance**: 1. For the authors's approach significance to be evaluated I would require a more extended discussion in the limitations about the sparsity of the point clouds and other failure cases of the method. 2. "Proper Experimental evaluation missing": The performance of the method by a simple adaptation of the base network is much worse in the canonical frame. The authors have not properly compared performance with 1) PCA canonicalization of the rotated point clouds 2) noisy versions
- The proposed invariant point cloud encoding can be easily used to modify current non-equivariant architectures into equivariant ones while retaining the expressivity required for the challenging task of point-cloud completion. - The experimental results highlight both the limitations of non-equivariant point-cloud completion methods when dealing with randomly rotated input-point clouds, as well as the benefits of utilizing the proposed equivariant alternative.
- This work does not compare or reference previous works on equivariant point cloud completion, specifically the work: [1] H. Wu and Y. Miao, "SO(3) Rotation Equivariant Point Cloud Completion using Attention-based Vector Neurons," 3DV (2022) - In the experimental evaluation, the non-equivariant methods are trained without using rotations as data augmentations. Since data augmentations are a commonly used alternative to equivariant networks, excluding them during training makes it harder to co
+ The paper addresses the impactful and challenging problem of 3D shape completion, under unknown orientation. + The proposed method is straightforward and easy to implement. + Compared to the baseline, the results are robust to rotation without requiring augmentation during training. + Introduces a rotation-invariant adaptation of AdaPointTr. + Proposes an anchor selection mechanism based on point curvature in the point cloud.
**Weaknesses:** - The claim that this is the first rotation-equivariant shape completion method is exaggerated. Other rotation-equivariant shape completion methods exist, such as [1], and [2] and [3] can also be easily adapted for shape completion. These methods should be addressed in the related work, and comparisons with [1] are necessary. - The usage of curvature for anchor point selection lacks motivation. - Given a partial point cloud, with large missing regions, such as a half aiplane; it
Simple orientation agnostic point cloud representation.
* The Transformer-Architecture is not described in the paper. It is necessary to rely on the descriptions of the AdaPoinTr and FoldNet papers to understand what is happening. I'd like to see a method section where first the things that are built upon are described concisely and then the exact changes are highlighted. This would allow the reader to see what is new and what has been around already. * As far as I can see the only new idea is to represent the input and output point clouds in the dis
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Taxonomy
TopicsMedical Image Segmentation Techniques · Image Processing and 3D Reconstruction · 3D Shape Modeling and Analysis
