REVIEW 3 major objections 4 minor 30 references
Floor-SP: Inverse CAD for Floorplans by Sequential Room-wise Shortest Path
T0 review · 3 major / 4 minor · reviewed 2026-08-14 · deepseek-v4-flash
Pith's one-line read A floorplan can be reconstructed from RGBD scans as a set of room loops by solving one shortest-path problem per room, and the paper shows this outperforms the prior state of the art.
desk verdict New formulation and dataset, but the headline FloorNet comparison may mix benchmarks and needs verification before the main claim is accepted. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the pixel-graph shortest-path reduction. Every pixel is a node; an edge between pixels carries a weight that collects one half of the corner cost at its two endpoints, the learned edge cost and room-mask penalty along the Bresenham line, a consistency discount that rewards pixels already used by other loops, and a fixed per-corner complexity charge. Fixing a start-edge and forbidding crossings of a perpendicular start-line enforces that the loop surrounds its room mask. Room-wise coordinate descent visits rooms in increasing order of area and solves this shortest-path problem for each, then repeats a second round to fix overlaps. A dominant-direction precomputation restricts candidate edges to a subset of global Manhattan frames, which is how the system extends beyond a single global Manhattan assumption.
What would settle it
Take a test scan and merge two adjacent rooms into a single mask by editing the Mask R-CNN output while keeping all sensor inputs identical, then rerun Floor-SP. The paper's Section 7.3 discussion predicts the final graph will contain one combined room with an incorrect shared-wall topology, because the energy has no term that can split a room proposal; observing a recovered two-room graph would refute the claimed dependence on room-count correctness.
Extended reading notes
Core claim
The central claim is that wall-graph inference for floorplans reduces to joint energy minimization over room loops once room segments are available. Each room's loop is a closed pixel sequence with an unknown number of corners; the paper defines data terms from DNN corner and edge likelihood maps plus a room-mask interior penalty, a consistency term over shared corner and edge pixels across all loops, and a model-complexity term counting corners. Minimizing this objective by room-wise coordinate descent, where each step is a shortest-path problem on a pixel graph with edge weights derived from the energy, yields the floorplan graph after simple loop merging. The paper's evidence is the quantitative comparison on 527 production-quality panorama RGBD scans, with 94 held out for testing: room precision/recall rises to 84.7/83.0 and Room++ to 51.4/50.4, against 81.2/72.1 and 42.3/37.5 for the prior system FloorNet.
Load-bearing premise
The load-bearing premise, conceded in the paper's Section 7.3 discussion, is that the initial room-segmentation step already determined the correct number of rooms and a roughly correct mask for each one; if a room is missed or two rooms are merged into one segment, no later stage can split or create rooms, so the final floorplan topology is wrong regardless of how well the shortest-path optimization runs.
Editorial extensions
If this is right
- If Floor-SP's central claim is right, floorplan reconstruction no longer has to commit to thresholded corner and edge detections; an optimizer can place and connect corners from learned cost maps.
- Because every room proposal is guaranteed a loop, room-level recall no longer collapses when a corner detector fires weakly on occluded walls, which is the mechanism behind the recall gains over FloorNet.
- The ablation table in the paper shows that removing the consistency term lowers Room++ precision/recall from 51.4/50.4 to 49.4/48.5, so shared-wall agreement is a source of the gain rather than an artifact of post-processing.
- The dominant-direction approximation means non-Manhattan rooms do not need one global Manhattan frame; each room can pick its own subset of up to four frames, which is why the system reports strong results on the non-Manhattan rooms in the test set.
- Two rounds of coordinate descent can repair overlaps and holes that a single round leaves, which is why the paper fixes the optimization to two rounds.
Reading between the lines
- A direct extension the paper leaves implicit is to let the optimizer correct the room count, for example by generating candidate loops from the corner and edge likelihood maps and accepting or rejecting them under the same energy; that would attack the dominant failure mode identified in Section 7.3.
- The coordinate-descent plus shortest-path pattern is not tied to floorplans; any reconstruction task whose output is a set of closed contours with learned per-pixel costs could reuse the reduction, such as building footprints, cadastral parcels, or cell boundaries in imagery.
- Because the paper notes that high-resolution panoramas and full 3D points are discarded, an untested extension is to feed those signals into the data terms; the reported corner-recall gap in occluded areas suggests this is where the next gain would come from.
- A testable prediction following from the paper's own failure analysis: on the subset of test units where the initial room segmentation has the correct number of rooms and roughly correct masks, room-level metrics should be near the top of the table, with almost all residual failures confined to non-Manhattan geometry and segmentation-count errors.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. Floor-SP reconstructs a floorplan from aligned panorama RGBD scans as multiple polygonal loops, one per room, by minimizing an energy that combines DNN-based corner/edge data terms, a consistency term encouraging rooms to share corners and walls, and a model-complexity penalty. The optimization is performed by room-wise coordinate descent, where each step is reduced to a shortest-path problem on a pixel graph. The paper evaluates the approach on 527 production-quality panorama scans (433 training, 94 test), deliberately making the test set challenging with 199 of 667 rooms non-Manhattan, and reports substantial improvements over FloorNet on Room and Room++ precision/recall metrics. Ablation experiments show the contribution of the data term, consistency term, and multiple coordinate-descent rounds.
Significance. If the reported comparison is valid, Floor-SP is a meaningful advance for floorplan reconstruction, particularly for non-Manhattan scenes, which previous optimization-based approaches handled poorly. The formulation is elegant: reducing multi-loop floorplan inference to a sequence of shortest-path problems with data and consistency terms is a creative and potentially influential idea. The release of code and data on the project website is a concrete strength that enables reproducibility and follow-up work. However, the central claim of a significant performance boost over the state of the art is currently undercut by a potentially uncontrolled comparison: the FloorNet baseline in Table 1 may be taken from the original FloorNet paper's 155-unit smartphone-video benchmark rather than re-evaluated on the same 94-unit panorama test split. If so, the reported gains are confounded by dataset, sensor, annotation protocol, and difficulty differences. The paper also explicitly acknowledges that room instance segmentation errors on the number of rooms cannot be recovered, which limits the method's robustness but is at least stated in Section 7.3.
major comments (3)
- [Section 7.2, Table 1] The headline comparison against FloorNet appears to mix benchmarks. The paper states that FloorNet was evaluated on 155 residential units with smartphone RGBD videos (Section 2), while Section 7 evaluates Floor-SP on a deliberately harder test split of 94 panorama scans with 199 of 667 non-Manhattan rooms. The text in Section 7.2 only says 'We follow FloorNet [20] and define metrics'; it never states that FloorNet was retrained or re-run on the same 94-unit test set, nor how FloorNet's video-based pipeline was adapted to the 4-channel top-down input. If the FloorNet row in Table 1 is the original published numbers, then the reported gains (Room 84.7/83.0 vs. 81.2/72.1; Room++ 51.4/50.4 vs. 42.3/37.5) compare different datasets, sensors, and difficulty levels, and do not support the central claim of a significant performance boost. Please clarify the experimental setup and, if the numbers are not from a matched evaluation, re-run a comparable baseline on the same test split or temper the claim accordingly.
- [Section 5, 'Containment constraint satisfaction'] The heuristic that fixes a start-edge and removes all intersecting edges to enforce loop containment breaks the local optimality of the coordinate-descent step, as the paper acknowledges. This means the reported energy minimization is not an exact solver of the stated objective; the claim that Floor-SP 'solves a shortest path problem to optimize the room structure' is therefore qualified. Since the start-edge selection depends on a corner candidates extracted from the likelihood map, the paper should at least analyze sensitivity to this choice (e.g., how often the selected start-edge is a true wall segment) or discuss the impact on the final energy. Without such analysis, the significance of the 'optimization' contribution relative to the prior heuristic system [17] is unclear.
- [Section 5, 'Sequential room-wise shortest path'] The coordinate descent is run for exactly two rounds, with no convergence criterion and no analysis of whether two rounds suffice. The claim that 'room-wise coordinate descent adds a further boost' is based on a single fixed number of iterations, and Figure 7 shows only two energy values. The paper should either run the descent to convergence and report the energy trajectory, or justify the two-round choice with evidence that additional rounds do not change the results. This is directly related to the central claim that the method optimizes the energy rather than merely applying a fixed number of heuristic passes.
minor comments (4)
- [Section 7.2, Table 1] No error bars, variance estimates, or per-unit paired statistics are reported for any metric in Table 1. Given that the reported Room++ differences are roughly 9 percentage points, the paper would be much stronger with confidence intervals or a paired analysis over the 94 test units to show that the differences are not driven by a few outliers.
- [Abstract and Section 1] The claim that the approach 'does not require corner/edge detection with thresholds' is overstated. The system uses a DRN to estimate corner and edge likelihoods, then extracts corner candidates and a start-edge using those maps (Section 5), and Mask R-CNN with a lowered detection threshold (Section 6). While the method avoids explicit threshold-based corner/edge detection as a final representation, threshold-like decisions are present in the pipeline.
- [Figure 7] The figure reports energy values after each coordinate-descent round, but the y-axis is not labeled and the absolute scale of the energy is not defined. Please clarify what energy is plotted (the total objective from Section 4?) and include units or a scale so the reader can interpret the claimed improvement.
- [Section 7.3] The paper should explicitly state in the conclusion that the method inherits the room-instance-segmentation errors and cannot split or create rooms, as it already does in the discussion. This is a known limitation, but it also means that the reported room-level metrics are partly determined by Mask R-CNN performance, so the paper should cite the Mask R-CNN room detection accuracy (e.g., how often the number of rooms is correct) to help the reader disentangle the contribution of the proposed optimization.
Circularity Check
No significant circularity: the room-wise shortest-path derivation and held-out evaluation are self-contained.
full rationale
The paper's derivation chain is self-contained. Section 4 defines a multi-loop energy as a sum of DNN-derived unary data terms, a consistency term, and a corner-count complexity term. Section 5 shows a direct algebraic reduction of this energy to shortest-path edge weights: the weights are exactly the pixel-wise costs plus lambda6 per corner, with the consistency terms rewritten as one-minus-indicator costs. No equation is identical to its input by construction; the containment constraint and EI_data penalty use the Mask R-CNN room segments as an upstream proposal, but the output loop is optimized over sensor-data likelihoods, and the paper explicitly acknowledges in Section 7.3 that errors in the number of room segments cannot be recovered. The DNN data terms are trained on 433 units and evaluated on a held-out 94-unit split, so room-level precision/recall is not a fitted quantity. Self-citations to [2], [17], and [20] provide conceptual inspiration and a baseline, but none is load-bearing: the shortest-path reduction, the coordinate-descent scheduling, and the consistency term are derived in the paper rather than imported. The FloorNet comparison in Table 1 may raise a benchmark-comparability concern, but that is an experimental-control issue, not a circularity of the derivation.
Assumptions & free parameters
free parameters (6)
- Energy weights λ1-λ6 =
λ1=0.2, λ2=0.2, λ3=100.0, λ4=0.2, λ5=0.1, λ6=1.0
- Mask R-CNN detection threshold =
0.2 (lowered from default 0.7)
- Room mask erosion iterations =
2 (8-connected)
- SPA bounding box dilation and margin =
10 dilation iterations, 5-pixel margin
- Number of dominant direction frames =
4 frames (8 directions)
- Coordinate descent rounds =
2
assumptions (6)
- domain assumption Floorplan boundaries can be represented as polygonal loops with pixel-aligned corners and straight edges.
- domain assumption The room segmentation provides the correct room partition (count and rough shape).
- domain assumption All wall directions can be captured by four Manhattan frames extracted globally and assigned per room.
- ad hoc to paper The start-line constraint enforces the containment of the room mask well enough.
- standard math Dijkstra's algorithm with non-negative edge weights solves every coordinate-descent subproblem exactly.
- domain assumption DNN likelihood models trained on the same dataset generalize to the test scans.
Cite this review
Pith. "Pith review of Floor-SP: Inverse CAD for Floorplans by Sequential Room-wise Shortest Path." pith.science (2026). https://pith.science/paper/P3REAOBJ
@misc{pith2026190806702,
author = {Pith},
title = {Pith review of: Floor-SP: Inverse CAD for Floorplans by Sequential Room-wise Shortest Path},
year = {2026},
howpublished = {\url{https://pith.science/paper/P3REAOBJ}},
note = {Machine review of arXiv:1908.06702}
}
read the original abstract
This paper proposes a new approach for automated floorplan reconstruction from RGBD scans, a major milestone in indoor mapping research. The approach, dubbed Floor-SP, formulates a novel optimization problem, where room-wise coordinate descent sequentially solves dynamic programming to optimize the floorplan graph structure. The objective function consists of data terms guided by deep neural networks, consistency terms encouraging adjacent rooms to share corners and walls, and the model complexity term. The approach does not require corner/edge detection with thresholds, unlike most other methods. We have evaluated our system on production-quality RGBD scans of 527 apartments or houses, including many units with non-Manhattan structures. Qualitative and quantitative evaluations demonstrate a significant performance boost over the current state-of-the-art. Please refer to our project website http://jcchen.me/floor-sp/ for code and data.
Figures
Figures from the paper (5 more)
Reference graph
Works this paper leans on
-
[20]
Floornet: A unified framework for floorplan reconstruction from 3d scans
Chen Liu, Jiaye Wu, and Yasutaka Furukawa. Floornet: A unified framework for floorplan reconstruction from 3d scans. In European Conference on Computer Vision (ECCV), 2018
work page 2018
-
[17]
Satoshi Ikehata, Hang Yang, and Yasutaka Furukawa. Struc- tured indoor modeling. In IEEE International Conference on Computer Vision (ICCV), 2015
work page 2015
-
[1]
3d semantic parsing of large-scale indoor spaces
Iro Armeni, Ozan Sener, Amir R Zamir, Helen Jiang, Ioannis Brilakis, Martin Fischer, and Silvio Savarese. 3d semantic parsing of large-scale indoor spaces. In IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 2016
work page 2016
-
[2]
Piecewise planar and compact floorplan reconstruction from images
Ricardo Cabral and Yasutaka Furukawa. Piecewise planar and compact floorplan reconstruction from images. In IEEE Conference on Computer Vision and Pattern Recognition (CVPR). IEEE, 2014
work page 2014
-
[3]
Realtime multi-person 2d pose estimation using part affinity fields
Zhe Cao, Tomas Simon, Shih-En Wei, and Yaser Sheikh. Realtime multi-person 2d pose estimation using part affinity fields. In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 2017
work page 2017
-
[4]
Angel X. Chang, Angela Dai, Thomas A. Funkhouser, Ma- ciej Halber, Matthias Nießner, Manolis Savva, Shuran Song, Andy Zeng, and Yinda Zhang. Matterport3d: Learning from rgb-d data in indoor environments. In 2017 International Conference on 3D Vision (3DV), 2017
work page 2017
-
[5]
Layout estimation of highly cluttered in- door scenes using geometric and semantic cues
Yu-Wei Chao, Wongun Choi, Caroline Pantofaru, and Sil- vio Savarese. Layout estimation of highly cluttered in- door scenes using geometric and semantic cues. In In- ternational Conference on Image Analysis and Processing (ICIAP), 2013
work page 2013
-
[6]
Scannet: Richly-annotated 3d reconstructions of indoor scenes
Angela Dai, Angel X Chang, Manolis Savva, Maciej Hal- ber, Thomas Funkhouser, and Matthias Nießner. Scannet: Richly-annotated 3d reconstructions of indoor scenes. In IEEE Conference on Computer Vision and Pattern Recog- nition (CVPR), 2017
work page 2017
Show all 30 references
-
[7]
https://github.com/multimodallearning/ pytorch-mask-rcnn
pytorch-mask-rcnn. https://github.com/multimodallearning/ pytorch-mask-rcnn
-
[8]
A dynamic programming approach to reconstructing build- ing interiors
Alex Flint, Christopher Mei, David Murray, and Ian Reid. A dynamic programming approach to reconstructing build- ing interiors. In European Conference on Computer Vision (ECCV), 2010
2010
-
[9]
Manhattan scene understanding using monocular, stereo, and 3d features
Alex Flint, David Murray, and Ian Reid. Manhattan scene understanding using monocular, stereo, and 3d features. In IEEE International Conference on Computer Vision (ICCV), 2011
2011
-
[10]
Deep ordinal regression net- work for monocular depth estimation
Huan Fu, Mingming Gong, Chaohui Wang, Kayhan Bat- manghelich, and Dacheng Tao. Deep ordinal regression net- work for monocular depth estimation. In IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 2018
2018
-
[11]
Seitz, and Richard Szeliski
Yasutaka Furukawa, Brian Curless, Steven M. Seitz, and Richard Szeliski. Manhattan-world stereo. In IEEE Com- puter Society Conference on Computer Vision and Pattern Recognition (CVPR), 2009
2009
-
[12]
Girshick
Kaiming He, Georgia Gkioxari, Piotr Doll ´ar, and Ross B. Girshick. Mask r-cnn. In IEEE International Conference on Computer Vision (ICCV), 2017
2017
-
[13]
Varsha Hedau, Derek Hoiem, and David A. Forsyth. Recov- ering the spatial layout of cluttered rooms. In IEEE Interna- tional Conference on Computer Vision (ICCV), 2009
2009
-
[14]
Learning structured inference neural networks with label relations
Hexiang Hu, Guang-Tong Zhou, Zhiwei Deng, Zicheng Liao, and Greg Mori. Learning structured inference neural networks with label relations. In IEEE Conference on Com- puter Vision and Pattern Recognition (CVPR), 2016
2016
-
[15]
Scenenn: A scene meshes dataset with annotations
Binh-Son Hua, Quang-Hieu Pham, Duc Thanh Nguyen, Minh-Khoi Tran, Lap-Fai Yu, and Sai-Kit Yeung. Scenenn: A scene meshes dataset with annotations. In 2016 Fourth International Conference on 3D Vision (3DV), 2016
2016
-
[16]
Learning to parse wireframes in images of man-made environments
Kun Huang, Yifan Wang, Zihan Zhou, Tianjiao Ding, Shenghua Gao, and Yi Ma. Learning to parse wireframes in images of man-made environments. In IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 2018
2018
-
[18]
Roomnet: End-to-end room layout estimation
Chen-Yu Lee, Vijay Badrinarayanan, Tomasz Malisiewicz, and Andrew Rabinovich. Roomnet: End-to-end room layout estimation. In IEEE International Conference on Computer Vision (ICCV), 2017
2017
-
[19]
Manhattan- world urban reconstruction from point clouds
Minglei Li, Peter Wonka, and Liangliang Nan. Manhattan- world urban reconstruction from point clouds. In European Conference on Computer Vision (ECCV), 2016
2016
-
[21]
Raster-to-vector: Revisiting floorplan transforma- tion
Chen Liu, Jiajun Wu, Pushmeet Kohli, and Yasutaka Fu- rukawa. Raster-to-vector: Revisiting floorplan transforma- tion. In IEEE International Conference on Computer Vision (ICCV), 2017
2017
-
[22]
Brostow, and Niloy Jyoti Mitra
Aron Monszpart, Nicolas Mellado, Gabriel J. Brostow, and Niloy Jyoti Mitra. Rapter: rebuilding man-made scenes with regular arrangements of planes. ACM Trans. Graph., 34:103:1–103:12, 2015
2015
-
[23]
Polyfit: Polygonal sur- face reconstruction from point clouds
Liangliang Nan and Peter Wonka. Polyfit: Polygonal sur- face reconstruction from point clouds. In IEEE International Conference on Computer Vision (ICCV), 2017
2017
-
[24]
Sch¨onberger, Silvano Galliani, Torsten Sattler, Konrad Schindler, Marc Pollefeys, and An- dreas Geiger
Thomas Sch ¨ops, Johannes L. Sch¨onberger, Silvano Galliani, Torsten Sattler, Konrad Schindler, Marc Pollefeys, and An- dreas Geiger. A multi-view stereo benchmark with high- resolution images and multi-camera videos. InIEEE Confer- ence on Computer Vision and Pattern Recognit...
2017
-
[25]
Efficient structured prediction for 3d indoor scene understanding
Alexander G Schwing, Tamir Hazan, Marc Pollefeys, and Raquel Urtasun. Efficient structured prediction for 3d indoor scene understanding. In IEEE Conference on Computer Vi- sion and Pattern Recognition (CVPR). IEEE, 2012
2012
-
[26]
Chang, Manolis Savva, and Thomas A
Shuran Song, Fisher Yu, Andy Zeng, Angel X. Chang, Manolis Savva, and Thomas A. Funkhouser. Semantic scene completion from a single depth image. In2017 IEEE Confer- ence on Computer Vision and Pattern Recognition (CVPR) , 2016
2016
-
[27]
Reconstructing the world’s museums.International Journal of Computer Vision, 110(3):243–258, 2014
Jianxiong Xiao and Yasutaka Furukawa. Reconstructing the world’s museums.International Journal of Computer Vision, 110(3):243–258, 2014
2014
-
[28]
Scene graph generation by iterative message passing
Danfei Xu, Yuke Zhu, Christopher B Choy, and Li Fei-Fei. Scene graph generation by iterative message passing. InPro- ceedings of the IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 2017
2017
-
[29]
Funkhouser
Fisher Yu, Vladlen Koltun, and Thomas A. Funkhouser. Di- lated residual networks. In IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 2017
2017
-
[30]
Bighand2
Shanxin Yuan, Qi Ye, Bjorn Stenger, Siddhant Jain, and Tae- Kyun Kim. Bighand2. 2m benchmark: Hand pose dataset and state of the art analysis. In IEEE Conference on Com- puter Vision and Pattern Recognition (CVPR), 2017
2017
Reviewed August 14, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.