REVIEW 5 major objections 6 minor 1 cited by
VAD-GS recovers missing geometry in dynamic urban scenes through voxel-based visibility reasoning and multi-view stereo densification.
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · deepseek-v4-flash
2026-08-04 10:28 UTC pith:XJBVJZ6M
load-bearing objection The paper has a sensible incremental method and one big unmeasured claim; send it to review with a request for direct geometry evaluation and artifacts. the 5 major comments →
VAD-GS: Visibility-Aware Densification for 3D Gaussian Splatting in Dynamic Urban Scenes
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The paper's central claim is that the quality ceiling of 3D Gaussian splatting in unbounded urban scenes is set by the completeness of initialization, and that this ceiling can be lifted by explicitly detecting and filling missing geometry. VAD-GS voxelizes the initial point cloud, rasterizes visible voxel surfaces with z-buffering to obtain a dense depth and index map, and compares that voxel-derived depth with the depth rendered from current Gaussians. Where the Gaussian depth is absent or too large, the region is flagged as unreliable. A diversity score then selects supporting views from different cameras and times that maximize lateral baseline and angular diversity, and a patch-matching
What carries the argument
The central object is the visible-voxel index map, a per-pixel record of the first voxel surface intersected by each ray after z-buffered rasterization of the voxelized point cloud. This map does three jobs: it provides dense geometric supervision where raw points are sparse, it maps each segmented object's pixels back to the 3D voxels that actually explain them, and it flags unreliable geometry whenever the depth rendered from Gaussian primitives is missing or significantly larger than the voxel depth. The second mechanism is the diversity-aware view-selection score, which rewards view pairs with dense, close voxel coverage, large lateral translation, small longitudinal motion, and large or
Load-bearing premise
The method assumes the initial 3D points are trustworthy enough to tell complete from incomplete geometry, and that missing surfaces are flat enough and consistently textured to be matched across cameras — objects that are entirely unobserved or that bend while moving break both assumptions.
What would settle it
Take a sequence containing a thin, high, low-texture traffic sign and a fast-moving pedestrian, with the sign absent from the LiDAR point cloud. If VAD-GS does not reconstruct the sign's planar surface (or reconstructs the pedestrian with warped, inconsistent patches and degraded depth maps relative to a method that handles non-rigid motion), then the central claim that MVS-guided densification recovers missing dynamic-scene geometry is not general.
If this is right
- Regions with no initial point coverage—such as a traffic sign above LiDAR range—can gain new Gaussian primitives rather than being filled by distorted background Gaussians.
- Dynamic vehicles can be densified by multi-view stereo when their moving observations are transformed into a local rigid coordinate frame and segmentation is accurate.
- Depth and normal supervision from MVS patches, added during optimization, suppresses floaters and produces consistently cleaner rendered geometry, not just better RGB.
- The method's densification is governed by explicit geometric priors instead of photometric gradients, reducing the case where occluded geometry receives erroneous updates.
- On sparser LiDAR data (32-beam scans), the geometry-recovery gains are larger than on dense scans, because the initialization gaps are more severe.
Where Pith is reading between the lines
- A testable extension is to apply the same voxel-visibility flagging to non-rigid objects by decomposing them into locally rigid parts; if that works, the main limitation named in the paper would be directly addressed.
- The view-selection score could be reused as a general sampling strategy in other multi-camera reconstruction pipelines, since it explicitly balances overlap and triangulation quality.
- The pipeline's reliance on instance segmentation and voxel geometry suggests that errors in either—especially for transparent or reflective surfaces—will be the first failure mode to appear in wider deployment, a prediction a reader could check by stress-testing on wire fences and glass.
- One could test whether the improved depth and normal maps translate to downstream autonomy tasks such as occupancy prediction or planning, which would make the geometric gains practically load-bearing.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes VAD-GS, a 3D Gaussian splatting framework for dynamic urban scenes. The method combines voxel-based visibility reasoning over the initialized point cloud, a diversity-aware view-selection score, and patch-match MVS reconstruction to densify Gaussians in regions where the initial geometry is incomplete or unreliable. The recovered MVS depth and normal priors are used both to initialize new Gaussian primitives and to supervise the optimization through additional geometric losses. The authors evaluate on the Waymo Open and nuScenes datasets, reporting PSNR/SSIM/LPIPS gains over prior dynamic-scene 3DGS methods and qualitatively cleaner depth and normal maps, and claim significant improvement in reconstructed geometry for both static and dynamic objects.
Significance. If the central claim is substantiated, VAD-GS would be a useful step toward making 3DGS robust to incomplete LiDAR/SfM initialization in unbounded dynamic scenes, and the extension of MVS-style reconstruction to dynamic multi-camera driving settings is a plausible and valuable direction. The paper also introduces a concrete, if heuristic, view-selection criterion and demonstrates a working integration of MVS priors into Gaussian densification. However, the strongest advertised result — improved geometric quality — is currently not directly measured, and several experimental and methodological issues leave the evidence base weaker than the claims. The contribution is potentially significant for the urban NVS community, but the manuscript needs substantial revision before the claims can be accepted at face value.
major comments (5)
- [Experiments — Ablation Study (Table 3)] The abstract and conclusion claim that VAD-GS 'significantly improves the quality of reconstructed geometry,' but no direct geometric metric is reported. The only quantitative support is photometric (PSNR/SSIM/LPIPS) plus qualitative depth/normal images. In Table 3, removing all geometric losses improves PSNR (24.59 vs. 24.51) and LPIPS (0.194 vs. 0.199) relative to the complete model, while the complete model wins only on PSNR* and SSIM. This means the reported photometric metrics do not track the claimed geometric improvement. Please add a direct geometry evaluation (e.g., Chamfer distance or F-score against held-out LiDAR or accumulated points, depth error against LiDAR range images) and discuss why the geometric losses do not improve photometric metrics.
- [MVS Reconstruction from Selected Views / Loss Function (Eq. 5)] There is a bootstrapping loop in the pipeline: patch hypotheses for MVS are initialized using 'real-world images and Gaussian-rendered results,' and the resulting MVS depth/normal maps are then used to supervise and densify the same Gaussian model through L_normal, L_hard, and L_soft. If the current Gaussian renderings contain missing geometry, floaters, or distorted surfaces, the loop can reinforce these errors rather than correct them. No experiment isolates this effect or validates the MVS output against independent geometry (e.g., held-out LiDAR scans). Please provide a non-circular validation, such as initializing MVS from a separately trained model or comparing MVS-produced depth against ground-truth range data, and quantify how much the densified points deviate from the real surfaces.
- [Voxel-Based Visibility Reasoning] The incomplete-region flagging mechanism compares Gaussian-rendered depth with the z-buffered voxel depth computed from the initialized point cloud. In exactly the motivating cases — objects above LiDAR range, sparse 32-beam nuScenes scans, fast-moving targets — the initial point cloud may have no voxels at all in the region that needs densification. The paper does not state how voxel-empty regions are detected or why they would be flagged for MVS reconstruction. Without such a mechanism, the method cannot 'actively evaluate structural completeness' in the hardest settings. Please clarify how the voxel index map handles uninitialized areas and provide statistics on how many MVS-densified regions had no initial voxel support.
- [Experiments — Table 2] Table 2 contains impossible metric values: the EmerNeRF entry for PSNR* is 0.346 and the NSG entry for LPIPS is 21.67; the MARS LPIPS value 0.905 is also implausible. These are outside the valid ranges for these metrics and strongly suggest a formatting or column-alignment error. Since Table 2 is the primary Waymo Open quantitative comparison, the current evidence for the 'consistently outperforms' claim on Waymo is unreliable. Please correct the table and re-run the comparison if needed.
- [Experiments and Limitations (Table 1, Limitations section)] The claim that VAD-GS improves geometry 'for both static and dynamic objects' is weakened by the paper's own limitation statement that MVS-based reconstruction assumes rigidity and 'degrades when handling deformable or non-rigid objects such as pedestrians.' The nuScenes results in Table 1 show that in several scenes, VAD-GS does not achieve the lowest LPIPS precisely because the dynamic objects are mostly pedestrians. Since pedestrians are a major component of urban dynamic scenes and nuScenes is one of only two benchmarks, the scope of the dynamic-object claim is narrower than stated. Please report object-class-conditional results or clearly restrict the claim to rigid dynamic objects such as vehicles.
minor comments (6)
- [Eq. (3)] The view-diversity score formula is ambiguous: the placement of N, the vector dot product, and the terms sqrt(tx^2+ty^2), |tz|, and sin(theta) lacks parentheses. Please define the dimensions of d_R and d_S and state whether higher or lower |tz| is preferred, matching the prose.
- [Supplementary Material] Several references are left as '(?)' placeholders, including 'prior methods such as (?)' in the supplement and '4DGS (?)' and 'SC-GS (?)' in the Limitations section. These must be completed.
- [Loss Function (Eq. 5)] The geometric loss weights lambda_normal, lambda_hard, and lambda_soft are said to follow Yan et al. (2024), but the actual values are not provided. Please report exact settings for reproducibility.
- [Ablation Study (Table 3)] The 'w/o voxel visibility reasoning' variant disables all downstream components (view selection and MVS), so it does not isolate the contribution of visibility reasoning itself. Consider an ablation that keeps view selection and MVS but removes only the visibility-based flagging, to separate the effects.
- [Experimental Setup] No error bars or multiple seeds are reported. With only 6 nuScenes scenes and 8 Waymo sequences, the per-scene comparisons would be more convincing with variance or paired tests. Also, the exclusion of nuScenes Scenes 02 and 07–09 should be justified as pre-registered criteria rather than post hoc selection.
- [Related Work / Baselines] The paper builds directly on GaussianPro and DNGaussian, but neither is included as a baseline. A comparison against these MVS/depth-guided densification methods would help isolate the contribution of the dynamic-scene components and clarify the claimed advantage.
Circularity Check
MVS geometric priors are seeded from the model's own renderings and then used to supervise the same model, so the claimed geometry recovery is partly a self-consistency loop rather than an independent measurement.
specific steps
-
fitted input called prediction
[Methodology > MVS Reconstruction from Selected Views; Eq. (5)]
"Patch hypotheses are initialized using real-world images and Gaussian-rendered results, and are iteratively refined by propagating candidates from neighboring pixels based on the assumption of local hypothesis similarity. ... Lnormal quantifies the angular deviations between the rendered surface normals and those obtained via patch matching, and Lhard and Lsoft quantify depth errors under hard and soft Gaussian opacity settings."
The MVS depth/normal maps are the target of the geometric losses in Eq. (5), but their patch hypotheses are initialized from the very Gaussian-rendered results that those losses are supposed to correct. Thus the 'geometric priors' are not independent of the optimized model: errors such as missing geometry, floaters, or distorted normals present in the current render can seed the MVS estimates and then be reinforced by Lnormal, Lhard, and Lsoft. The paper reports improved rendered depth/normal maps, but no held-out geometry metric (e.g., comparing the new MVS points or rendered depth against LiDAR) isolates the MVS contribution; the loop can therefore masquerade as geometry recovery even when it only re-imitates the current render.
full rationale
The paper's rendering-quality claim is grounded in held-out image comparisons against external baselines on Waymo and nuScenes, so it is not circular. The voxel-visibility reasoning and view-selection components are heuristics evaluated on public datasets and do not reduce to a fitted parameter or self-citation. However, the geometry-improvement claim is weakened by a genuine bootstrapping loop: MVS patch hypotheses are explicitly initialized using Gaussian-rendered results, and the resulting depth/normal priors are then used as supervision in Eq. (5) for the same Gaussian model. This makes the 'geometric priors' partly a function of the current model rather than an independent ground truth. The paper's own ablation (Table 3) shows that removing the geometric losses improves PSNR and LPIPS, underscoring that the photometric metrics do not directly validate the geometry claim. No load-bearing self-citation or imported uniqueness theorem was found; the circularity is partial, not total, because MVS also uses real-world images and multi-view consistency checks. Overall score 4 reflects a partially circular geometry-validation loop while acknowledging the independent photometric core.
Axiom & Free-Parameter Ledger
free parameters (6)
- geometric loss weights λ_normal, λ_hard, λ_soft =
not reported; set following Yan et al. 2024
- voxel resolution for visibility voxelization =
not reported
- number of supporting views k =
not reported
- view-sampling noise scale ε =
not reported
- depth-comparison thresholds for flagging incomplete instances =
not reported
- densification interval =
every 5 complete sampling cycles
axioms (6)
- domain assumption Initialized point cloud (LiDAR/SfM) provides a sufficient base for voxelization and visibility reasoning.
- domain assumption Scene surfaces are locally piecewise planar, and photometric consistency is a valid matching signal.
- domain assumption Dynamic objects are rigid in their local coordinate frame.
- domain assumption Offline instance segmentation produces sufficiently accurate masks for static/dynamic separation.
- domain assumption Z-buffered rasterization of voxelized points yields correct surface visibility and depth.
- standard math 3DGS alpha-blending and covariance parameterization are valid rendering models.
Cite this review
Pith. "Pith review of VAD-GS: Visibility-Aware Densification for 3D Gaussian Splatting in Dynamic Urban Scenes." pith.science (2026). https://pith.science/paper/XJBVJZ6M
@misc{pith2026251009364,
author = {Pith},
title = {Pith review of: VAD-GS: Visibility-Aware Densification for 3D Gaussian Splatting in Dynamic Urban Scenes},
year = {2026},
howpublished = {\url{https://pith.science/paper/XJBVJZ6M}},
note = {Machine review of arXiv:2510.09364}
}
read the original abstract
3D Gaussian splatting (3DGS) has demonstrated impressive performance in synthesizing high-fidelity novel views. Nonetheless, its effectiveness critically depends on the quality of the initialized point cloud. Specifically, achieving uniform and complete point coverage over the underlying scene structure requires overlapping observation frustums, an assumption that is often violated in unbounded, dynamic urban environments. Training Gaussian models with partially initialized point clouds often leads to distortions and artifacts, as camera rays may fail to intersect valid surfaces, resulting in incorrect gradient propagation to Gaussian primitives associated with occluded or invisible geometry. Additionally, existing densification strategies simply clone and split Gaussian primitives from existing ones, incapable of reconstructing geometry from missing structures. To address these limitations, we propose VAD-GS, a 3DGS framework tailored for geometry recovery in challenging urban scenes. Our method identifies unreliable geometry structures via voxel-based visibility reasoning, selects informative supporting views through diversity-aware view selection, and recovers missing structures via multi-view stereo reconstruction. This design enables the generation of new Gaussian primitives guided by reliable geometric priors, even in regions lacking initial points. Extensive experiments on the Waymo and nuScenes datasets demonstrate that VAD-GS outperforms state-of-the-art 3DGS approaches and significantly improves the quality of reconstructed geometry for both static and dynamic objects. Our project webpage is at mias.group/VAD-GS.
Figures
Forward citations
Cited by 1 Pith paper
-
Uncertainty-driven 3D Gaussian Splatting Active Mapping via Anisotropic Visibility Field
GAVIS quantifies per-particle anisotropic visibility in 3DGS via spherical harmonics, integrates it into a Bayesian rasterizer for real-time uncertainty, and uses maximum information gain for active mapping.
Reference graph
Works this paper leans on
-
[1]
, " * write output.state after.block = add.period write newline
ENTRY address archivePrefix author booktitle chapter edition editor eid eprint howpublished institution isbn journal key month note number organization pages publisher school series title type volume year label extra.label sort.label short.list INTEGERS output.state before.all mid.sentence after.sentence after.block FUNCTION init.state.consts #0 'before.a...
-
[2]
write newline
" write newline "" before.all 'output.state := FUNCTION n.dashify 't := "" t empty not t #1 #1 substring "-" = t #1 #2 substring "--" = not "--" * t #2 global.max substring 't := t #1 #1 substring "-" = "-" * t #2 global.max substring 't := while if t #1 #1 substring * t #2 global.max substring 't := if while FUNCTION word.in bbl.in capitalize " " * FUNCT...
-
[3]
Aan s, H.; et al. 2016. Large-scale data for multiple-view stereopsis. International Journal of Computer Vision, 120: 153--168
2016
-
[4]
Bao, Y.; et al. 2025. 3D Gaussian splatting: Survey, technologies, challenges, and opportunities. IEEE Transactions on Circuits and Systems for Video Technology, 35: 6832--6852
2025
-
[5]
T.; et al
Barron, J. T.; et al. 2021. Mip-NeRF: A multiscale representation for anti-aliasing neural radiance fields. In Proceedings of the IEEE/CVF International Conference on Computer Vision (ICCV), 5855--5864
2021
-
[6]
T.; et al
Barron, J. T.; et al. 2022. Mip-NeRF 360: Unbounded anti-aliased neural radiance fields. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 5470--5479
2022
-
[7]
Caesar, H.; et al. 2020. nuScenes: A multimodal dataset for autonomous driving. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 11621--11631
2020
-
[8]
Chen, Y.; et al. 2024. Periodic vibration Gaussian: Dynamic urban scene reconstruction and real-time rendering. arXiv:2311.18561
Pith/arXiv arXiv 2024
-
[9]
Chen, Z.; et al. 2025. OmniRe: Omni urban scene reconstruction. In Proceedings of the International Conference on Learning Representations (ICLR), 85508--85527
2025
-
[10]
Cheng, K.; et al. 2024. GaussianPro: 3D Gaussian splatting with progressive propagation. In Proceedings of the International Conference on Machine Learning (ICML), 8123--8140
2024
-
[11]
Cheng, S.; et al. 2020. Deep stereo using adaptive thin volume representation with uncertainty awareness. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 2524--2534
2020
-
[12]
Dai, A.; et al. 2017. ScanNet: Richly-annotated 3D reconstructions of indoor scenes. In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 5828--5839
2017
-
[13]
Dosovitskiy, A.; et al. 2017. CARLA: An open urban driving simulator. In Conference on Robot Learning (CoRL), 1--16
2017
-
[14]
Hou, Y.; Kannala, J.; and Solin, A. 2019. Multi-view stereo by temporal nonparametric fusion. In Proceedings of the IEEE/CVF International Conference on Computer Vision (ICCV), 2651--2660
2019
-
[15]
Jiang, H.; et al. 2024. GeoTexDensifier: Geometry-texture-aware densification for high-quality photorealistic 3D Gaussian splatting. arXiv:2412.16809
arXiv 2024
-
[16]
Kerbl, B.; et al. 2023. 3D Gaussian splatting for real-time radiance field rendering. ACM Transactions on Graphics, 42(4): 1--14
2023
-
[17]
Kerbl, B.; et al. 2024. A hierarchical 3D Gaussian representation for real-time rendering of very large datasets. ACM Transactions on Graphics, 43(4): 1--15
2024
-
[18]
Kirillov, A.; et al. 2023. Segment anything. In Proceedings of the IEEE/CVF International Conference on Computer Vision (ICCV), 4015--4026
2023
-
[19]
Li, J.; et al. 2024. DNGaussian: Optimizing sparse-view 3D Gaussian radiance fields with global-local depth normalization. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 20775--20785
2024
-
[20]
Mildenhall, B.; et al. 2021. NeRF: Representing scenes as neural radiance fields for view synthesis. Communications of the ACM, 65(1): 99--106
2021
-
[21]
M \"u ller, T.; et al. 2022. Instant neural graphics primitives with a multiresolution hash encoding. ACM Transactions on Graphics, 41(4): 1--15
2022
-
[22]
Ost, J.; et al. 2021. Neural scene graphs for dynamic scenes. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 2856--2865
2021
-
[23]
Ranftl, R.; et al. 2021. Vision Transformers for dense prediction. In Proceedings of the IEEE/CVF International Conference on Computer Vision (ICCV), 12179--12188
2021
-
[24]
L.; and Frahm, J.-M
Schonberger, J. L.; and Frahm, J.-M. 2016. Structure-from-motion revisited. In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 4104--4113
2016
-
[25]
Schops, T.; et al. 2017. A multi-view stereo benchmark with high-resolution images and multi-camera videos. In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 3260--3269
2017
-
[26]
Sun, P.; et al. 2020. Scalability in perception for autonomous driving: Waymo Open dataset. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 2446--2454
2020
-
[27]
Wang, F.; et al. 2021. PatchmatchNet: Learned multi-view patchmatch stereo. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 14194--14203
2021
-
[28]
Wang, F.; et al. 2024. Learning-based Multi-View Stereo: A Survey. arXiv:2408.15235
arXiv 2024
-
[29]
Wei, D.; Li, Z.; et al. 2025. Omni-Scene: Omni-Gaussian representation for ego-centric sparse-view scene reconstruction. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 22317--22327
2025
-
[30]
Wu, G.; et al. 2024. 4D Gaussian splatting for real-time dynamic scene rendering. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 20310--20320
2024
-
[31]
Wu, Z.; et al. 2023. MARS: An instance-aware, modular and realistic simulator for autonomous driving. In Proceedings of the CAAI International Conference on Artificial Intelligence (CICAI), 3--15. Springer
2023
-
[32]
Xu, Q.; and Tao, W. 2020. Planar prior assisted patchmatch multi-view stereo. In Proceedings of the AAAI conference on artificial intelligence (AAAI), 12516--12523
2020
-
[33]
Yan, Y.; et al. 2024. Street Gaussians: Modeling dynamic urban scenes with Gaussian splatting. In Proceedings of the European Conference on Computer Vision (ECCV), 156--173. Springer
2024
-
[34]
Yang, J.; et al. 2022. Non-parametric depth distribution modelling based depth inference for multi-view stereo. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 8626--8634
2022
-
[35]
Yang, J.; et al. 2023. EmerNeRF: Emergent spatial-temporal scene decomposition via self-supervision. arXiv:2311.02077
Pith/arXiv arXiv 2023
-
[36]
Yao, Y.; et al. 2018. MVSNet: Depth inference for unstructured multi-view stereo. In Proceedings of the European Conference on Computer Vision (ECCV), 767--783
2018
-
[37]
Zhang, Z.; et al. 2024. Pixel-GS: Density control with pixel-aware gradient for 3D Gaussian splatting. In Proceedings of the European Conference on Computer Vision (ECCV), 326--342. Springer
2024
-
[38]
Zhou, X.; et al. 2024. DrivingGaussian: Composite Gaussian splatting for surrounding dynamic autonomous driving scenes. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 21634--21643
2024
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.