| 1. |
- Arcelli, Carlo, et al.
(författare)
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Computing and analysing convex deficiencies to characterise 3D complex objects
- 2005
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Ingår i: Image and Vision Computing: Discrete Geometry for Computer Imagery. ; 23:2, s. 203-211
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Tidskriftsartikel (refereegranskat)abstract
- Entities such as object components, cavities, tunnels and concavities in 3D digital images can be useful in the framework of object analysis. For each object component, we first identify its convex deficiencies, by subtracting the object component from a covering polyhedron approximating the convex hull. Watershed segmentation is then used to decompose complex convex deficiencies into simpler parts, corresponding to individual cavities, concavities and tunnels of the object component. These entities are finally described by means of a representation system accounting for the shape features characterising them.
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| 2. |
- Batstone, Kenneth, et al.
(författare)
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Collaborative merging of radio SLAM maps in view of crowd-sourced data acquisition and big data
- 2019
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Ingår i: ICPRAM 2019 - Proceedings of the 8th International Conference on Pattern Recognition Applications and Methods. - : SCITEPRESS - Science and Technology Publications. - 9789897583513 ; , s. 807-813
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Konferensbidrag (refereegranskat)abstract
- Indoor localization and navigation is a much researched and difficult problem. The best solutions, usually use expensive specialized equipment and/or prior calibration of some form. To the average person with smart or Internet-Of-Things devices, these solutions are not feasible, particularly in large scales. With hardware advancements making Ultra-Wideband devices more accurate and low powered, this unlocks the potential of having such devices in commonplace around factories and homes, enabling an alternative method of navigation. Therefore, indoor anchor calibration becomes a key problem in order to implement these devices efficiently and effectively. In this paper, we present a method to fuse radio SLAM (also known as Time-Of-Arrival self-calibration) maps together in a linear way. In doing so we are then able to collaboratively calibrate the anchor positions in 3D to native precision of the devices. Furthermore, we introduce an automatic scheme to determine which of the maps are best to use to further improve the anchor calibration and its robustness but also show which maps could be discarded. Additionally, when a map is fused in a linear way, it is a very computationally cheap process and produces a reasonable map which is required to push for crowd-sourced data acquisition.
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| 3. |
- Borgefors, Gunilla, et al.
(författare)
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Computing skeletons in three dimensions
- 1999
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Ingår i: Pattern Recognition. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0031-3203 .- 1873-5142. ; 32:7, s. 1225-1236
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Tidskriftsartikel (refereegranskat)abstract
- Skeletonization will probably become as valuable a tool for shape analysis in 3D, as it is in 2D. We present a topology preserving 3D skeletonization method which computes both surface and curve skeletons whose voxels are labelled with the D-6 distance to
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| 4. |
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| 5. |
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| 6. |
- Borgefors, Gunilla, et al.
(författare)
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Discrete Skeletons from Distance Transforms in 2D and 3D
- 2008
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Ingår i: Medial Representations. - Netherlands : Springer Verlag. ; , s. 155-190
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- We present discrete methods to compute the digital skeleton of shapes in 2D and 3D images. In 2D, the skeleton is a set of curves, while in 3D it will be a set of surfaces and curves, the surface skeleton, or a set of curves, the curve skeleton. A general scheme could, in principle, be followed for both 2D and 3D discrete skeletonization. However, we will describe one approach for 2D skeletonization, mainly based on marking in the distance transform the shape elements that should be assigned to the skeleton, and another approach for 3D skeletonization, mainly based on iterated element removal. In both cases, the distance transform of the image will play a key role to obtain skeletons reflecting important shape features such as symmetry, elongation, and width.
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| 7. |
- Borgefors, Gunilla, et al.
(författare)
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Skeletonizing Volume Objects. Part II : From Surface to Curve Skeleton
- 1998
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Ingår i: Advances in Pattern Recognition Joint IAPR International Workshops SSPR'98 and SPR'98 Sydney, Australia, August 11–13, 1998 Proceedings. - : Springer Verlag. - 9783540648581 ; , s. 220-229
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Konferensbidrag (refereegranskat)abstract
- Volume imaging techniques are becoming common and skeletonization has begun to prove valuable for shape analysis also in 3D. In this paper, a method to reduce solid volume objects to their 3D curve skeletons is presented. The method consists of two major steps.
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| 8. |
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| 9. |
- Flood, Gabrielle, et al.
(författare)
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Stochastic Analysis of Time-Difference and Doppler Estimates for Audio Signals
- 2019
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Ingår i: Pattern Recognition Applications and Methods - 7th International Conference, ICPRAM 2018, Revised Selected Papers. - Cham : Springer International Publishing. - 1611-3349 .- 0302-9743. - 9783030054984 ; 11351 LNCS, s. 116-138
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Konferensbidrag (refereegranskat)abstract
- Pairwise comparison of sound and radio signals can be used to estimate the distance between two units that send and receive signals. In a similar way it is possible to estimate differences of distances by correlating two received signals. There are essentially two groups of such methods, namely methods that are robust to noise and reverberation, but give limited precision and sub-sample refinements that are more sensitive to noise, but also give higher precision when they are initialized close to the real translation. In this paper, we present stochastic models that can explain the precision limits of such sub-sample time-difference estimates. Using these models new methods are provided for precise estimates of time-differences as well as Doppler effects. The developed methods are evaluated and verified on both synthetic and real data.
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| 10. |
- Li, Zhongguo, et al.
(författare)
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Template based human pose and shape estimation from a single RGB-D image
- 2019
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Ingår i: ICPRAM 2019 - Proceedings of the 8th International Conference on Pattern Recognition Applications and Methods. - : SCITEPRESS - Science and Technology Publications. - 9789897583513 ; , s. 574-581
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Konferensbidrag (refereegranskat)abstract
- Estimating the 3D model of the human body is needed for many applications. However, this is a challenging problem since the human body inherently has a high complexity due to self-occlusions and articulation. We present a method to reconstruct the 3D human body model from a single RGB-D image. 2D joint points are firstly predicted by a CNN-based model called convolutional pose machine, and the 3D joint points are calculated using the depth image. Then, we propose to utilize both 2D and 3D joint points, which provide more information, to fit a parametric body model (SMPL). This is implemented through minimizing an objective function, which measures the difference of the joint points between the observed model and the parametric model. The pose and shape parameters of the body are obtained through optimization and the final 3D model is estimated. The experiments on synthetic data and real data demonstrate that our method can estimate the 3D human body model correctly.
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| 11. |
- Nyström, Ingela, et al.
(författare)
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2D grey-level convex hull computation: a discrete 3D approach
- 2003
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Konferensbidrag (refereegranskat)abstract
- We compute discrete convex hulls in 2D grey-level images, where we interpret grey-level values as heights in 3D landscapes. For these 3D objects, using a 3D binary method, we compute approximations of their convex hulls. Differently from other grey-level
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| 12. |
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| 13. |
- Nyström, Ingela, et al.
(författare)
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Skeletonization in 3D Discrete Binary Images
- 2005
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Ingår i: Handbook of Pattern Recognition and Computer Vision, 3rd edition. - : World Scientific, Singapore. - 9812561056 ; , s. 137-156
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Bokkapitel (populärvet., debatt m.m.)abstract
- Skeletonization is a way to reduce dimensionality of digital objects. Here, we present in detail an algorithm that computes the curve skeleton of a solid object, i.e., an object without cavities, in a 3D binary image. The algorithm consists of three main steps. During the first step, the surface skeleton is detected, by directly marking in the distance transform of the object the voxels that should be assigned to the surface skeleton. The curve skeleton is then computed by iteratively thinning the surface skeleton, during the second step. Finally, the third step is performed to reduce the curve skeleton to unit width and to prune, in a controlled manner, some of its peripheral branches.
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| 14. |
- Saha, Punam K., et al.
(författare)
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A survey on skeletonization algorithms and their applications
- 2016
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Ingår i: Pattern Recognition Letters. - : Elsevier BV. - 0167-8655 .- 1872-7344. ; 76, s. 3-12
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Tidskriftsartikel (refereegranskat)abstract
- Skeletonization provides an effective and compact representation of objects, which is useful for object description, retrieval, manipulation, matching, registration, tracking, recognition, and compression. It also facilitates efficient assessment of local object properties, e.g., scale, orientation, topology, etc. Several computational approaches are available in literature toward extracting the skeleton of an object, some of which are widely different in terms of their principles. In this paper, we present a comprehensive and concise survey of different skeletonization algorithms and discuss their principles, challenges, and benefits. Topology preservation, parallelization, and multi-scale skeletonization approaches are discussed. Finally, various applications of skeletonization are reviewed and the fundamental challenges of assessing the performance of different skeletonization algorithms are discussed.
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| 15. |
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| 16. |
- Sanniti di Baja, Gabriella, et al.
(författare)
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2D grey-level skeleton computation: A discrete 3D approach
- 2004
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Ingår i: Proceedings of International Conference on Pattern Recognition (ICPR 2004).
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Konferensbidrag (refereegranskat)abstract
- A discrete 3D binary approach to compute the skeleton in 2D grey-level images is presented. The 2D grey-level input image is converted to a 3D binary image and the top surface of the foreground is identified. This discrete surface then undergoes skeletonization. The obtained 3D curve skeleton is pruned, before being projected back to a 2D grey-level image. This is suitably post-processed, since the projection may cause spurious loops and thickening. This algorithm can find applications in optical character recognition and document analysis or in other situations where shape analysis by skeletons is desired. An important property of the suggested method is that no hard segmentation into foreground and background is needed prior to the skeletonization.
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| 17. |
- Sanniti di Baja, Gabriella, et al.
(författare)
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A new shape descriptor for surfaces in 3D images
- 2002
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Ingår i: Pattern Recognition Letters. ; 23:6, s. 703-711
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Tidskriftsartikel (refereegranskat)abstract
- We introduce a linear shape descriptor for (open) surfaces in 3D images. To extract the shape descriptor, the border of the surface is first identified. Then, the distance transform of the surface is computed, where each voxel in the surface is labelled w
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| 18. |
- Sanniti di Baja, Gabriella, et al.
(författare)
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Discrete 3D tools applied to 2D grey-level images
- 2005
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Ingår i: Image Analysis and Processing - ICIAP 2005. - 3540288694 ; , s. 229-236
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Konferensbidrag (refereegranskat)abstract
- 2D grey-level images are interpreted as 3D binary images, where the grey-level plays the role of the third coordinate. In this way, algorithms devised for 3D binary images can be used to analyse 2D grey-level images. Here, we present three such algorithms. The first algorithm smoothes a 2D grey-level image by flattening its geometrical and grey-level peaks while simultaneously filling in geometrical and grey-level valleys, regarded as non significant in the problem domain. The second algorithm computes an approximation of the convex hull of a 2D grey-level object, by building a covering polyhedron closely fitting the corresponding object in a 3D binary image. The result obtained is convex both from the geometrical point of view and as concerns grey-levels. The third algorithm skeletonizes a 2D grey-level object by skeletonizing the top surface of the object in the corresponding 3D binary image.
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| 19. |
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| 20. |
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| 21. |
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| 22. |
- Svensson, Stina and Sanniti di Baja, Gabriella
(författare)
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Simplifying curve skeletons in volume images
- 2003
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Ingår i: Computer Vision and Image Understanding. ; 90, s. 242-257
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The curve skeleton of a 3D solid object provides a useful tool for shape
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| 23. |
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| 24. |
- Svensson, Stina, et al.
(författare)
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Curve skeletonization of surface-like objects in 3D images guided by voxel classification
- 2002
-
Ingår i: Pattern Recognition Letters. - 0167-8655 .- 1872-7344. ; 23:12, s. 1419-1426
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Tidskriftsartikel (refereegranskat)abstract
- Skeletonization is a way to reduce dimensionality of digital objects. Here, we present an algorithm that computes the curve skeleton of a surface-like object in a 3D image, i.e., an object that in one of the three dimensions is at most two-voxel thick. A
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| 25. |
- Svensson, Stina, et al.
(författare)
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Finding Cavities and Tunnels in 3D Complex Objects
- 2003
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Konferensbidrag (refereegranskat)abstract
- Topological properties are global features that can be useful for recognition of digital objects. For example, this is the case for objects having complex shape without being decomposable into meaningful simple parts. In the case of 3D binary images, top
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| 26. |
- Svensson, Stina, et al.
(författare)
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Using distance transforms to decompose 3D discrete objects
- 2002
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Ingår i: Image and Vision Computing. ; 20:8, s. 529-
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Tidskriftsartikel (refereegranskat)abstract
- Object decomposition into simpler parts greatly diminishes the complexity of a recognition task. In this paper, we present a method to decompose a 3D discrete object into nearly convex or elongated parts. Object decomposition is guided by the distance tra
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| 27. |
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| 28. |
- Valtonen Örnhag, Marcus, et al.
(författare)
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Enforcing the General Planar Motion Model : Bundle Adjustment for Planar Scenes
- 2020
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Ingår i: Pattern Recognition Applications and Methods - 8th International Conference, ICPRAM 2019, Revised Selected Papers. - Cham : Springer International Publishing. - 0302-9743 .- 1611-3349. - 9783030400132 ; 11996 LNCS, s. 119-135
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Konferensbidrag (refereegranskat)abstract
- In this paper we consider the case of planar motion, where a mobile platform equipped with two cameras moves freely on a planar surface. The cameras are assumed to be directed towards the floor, as well as being connected by a rigid body motion, which constrains the relative motion of the cameras and introduces new geometric constraints. In the existing literature, there are several algorithms available to obtain planar motion compatible homographies. These methods, however, do not minimise a physically meaningful quantity, which may lead to issues when tracking the mobile platform globally. As a remedy, we propose a bundle adjustment algorithm tailored for the specific problem geometry. Due to the new constrained model, general bundle adjustment frameworks, compatible with the standard six degree of freedom model, are not directly applicable, and we propose an efficient method to reduce the computational complexity, by utilising the sparse structure of the problem. We explore the impact of different polynomial solvers on synthetic data, and highlight various trade-offs between speed and accuracy. Furthermore, on real data, the proposed method shows an improvement compared to generic methods not enforcing the general planar motion model.
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| 29. |
- Örnhag, Marcus Valtonen, et al.
(författare)
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Efficient Radial Distortion Correction for Planar Motion
- 2020
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Ingår i: Pattern Recognition Applications and Methods - 9th International Conference, ICPRAM 2020, Revised Selected Papers. - Cham : Springer International Publishing. - 1611-3349 .- 0302-9743. - 9783030661243 ; 12594 LNCS, s. 46-63
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Konferensbidrag (refereegranskat)abstract
- In this paper we investigate simultaneous radial distortion calibration and motion estimation for vehicles travelling parallel to planar surfaces. This is done by estimating the inter-image homography between two poses, as well as the distortion parameter. Radial distortion correction is often performed as a pre-calibration step; however, accurately estimating the distortion profile without special scene requirements may make such procedures obsolete. As many modern day consumer cameras are affected by radial distortion to some degree, there is a great potential to reduce production time, if properly implemented. We devise two polynomial solvers, for radially distorted homographies compatible with different models of planar motion. We show that the algorithms are numerically stable, and sufficiently fast to be incorporated in a real-time frameworks. Furthermore, we show on both synthetic and real data, that the proposed solvers perform well compared to competing methods.
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| 30. |
- Örnhag, Marcus Valtonen, et al.
(författare)
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Fast Non-minimal Solvers for Planar Motion Compatible Homographies
- 2019
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Ingår i: ICPRAM 2019 - Proceedings of the 8th International Conference on Pattern Recognition Applications and Methods. - : SCITEPRESS - Science and Technology Publications. - 9789897583513 ; , s. 40-51
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Konferensbidrag (refereegranskat)abstract
- This paper presents a novel polynomial constraint for homographies compatible with the general planar motion model. In this setting, compatible homographies have five degrees of freedom-instead of the general case of eight degrees of freedom-and, as a consequence, a minimal solver requires 2.5 point correspondences. The existing minimal solver, however, is computationally expensive, and we propose using non-minimal solvers, which significantly reduces the execution time of obtaining a compatible homography, with accuracy and robustness comparable to that of the minimal solver. The proposed solvers are compared with the minimal solver and the traditional 4-point solver on synthetic and real data, and demonstrate good performance, in terms of speed and accuracy. By decomposing the homographies obtained from the different methods, it is shown that the proposed solvers have future potential to be incorporated in a complete Simultaneous Localization and Mapping (SLAM) framework.
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| 31. |
- Örnhag, Marcus Valtonen, et al.
(författare)
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Planar motion bundle adjustment
- 2019
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Ingår i: ICPRAM 2019 - Proceedings of the 8th International Conference on Pattern Recognition Applications and Methods. - : SCITEPRESS - Science and Technology Publications. - 9789897583513 ; , s. 24-31
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Konferensbidrag (refereegranskat)abstract
- In this paper we consider trajectory recovery for two cameras directed towards the floor, and which are mounted rigidly on a mobile platform. Previous work for this specific problem geometry has focused on locally minimising an algebraic error between inter-image homographies to estimate the relative pose. In order to accurately track the platform globally it is necessary to refine the estimation of the camera poses and 3D locations of the feature points, which is commonly done by utilising bundle adjustment; however, existing software packages providing such methods do not take the specific problem geometry into account, and the result is a physically inconsistent solution. We develop a bundle adjustment algorithm which incorporates the planar motion constraint, and devise a scheme that utilises the sparse structure of the problem. Experiments are carried out on real data and the proposed algorithm shows an improvement compared to established generic methods.
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| 32. |
- Örnhag, Marcus Valtonen, et al.
(författare)
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Radially distorted planar motion compatible homographies
- 2020
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Ingår i: Proceedings of the 9th International Conference on Pattern Recognition Applications and Methods : ICPRAM 2020 - ICPRAM 2020. - : SCITEPRESS - Science and Technology Publications. - 9789897583971 ; 1, s. 280-288
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Konferensbidrag (refereegranskat)abstract
- Fast and accurate homography estimation is essential to many computer vision applications, including scene degenerate cases and planarity detection. Such cases arise naturally in man-made environments, and failure to handle them will result in poor positioning estimates. Most modern day consumer cameras are affected by some level of radial distortion, which must be compensated for in order to get accurate estimates. This often demands calibration procedures, with specific scene requirements, and off-line processing. In this paper a novel polynomial solver for radially distorted planar motion compatible homographies is presented. The proposed algorithm is fast and numerically stable, and is proven on both synthetic and real data to work well inside a RANSAC loop.
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| 33. |
- Örnhag, Marcus Valtonen, et al.
(författare)
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Relative pose estimation in binocular vision for a planar scene using inter-image homographies
- 2018
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Ingår i: ICPRAM 2018 - Proceedings of the 7th International Conference on Pattern Recognition Applications and Methods. - : SCITEPRESS - Science and Technology Publications. - 9789897582769 ; 2018-January, s. 568-575
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Konferensbidrag (refereegranskat)abstract
- In this paper we consider a mobile platform with two cameras directed towards the floor mounted the same distance from the ground, assuming planar motion and constant internal parameters. Earlier work related to this specific problem geometry has been carried out for monocular systems, and the main contribution of this paper is the generalization to a binocular system and the recovery of the relative translation and orientation between the cameras. The method is based on previous work on monocular systems, using sequences of inter-image homographies. Experiments are conducted using synthetic data, and the results demonstrate a robust method for determining the relative parameters.
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