Lukáš Hruda

Bio: Lukáš Hruda is an academic researcher from University of West Bohemia. The author has contributed to research in topics: Symmetry (geometry) & Reflection symmetry. The author has an hindex of 2, co-authored 5 publications receiving 9 citations.

On Evaluating Consensus in RANSAC Surface Registration

Abstract: The topic of the article is new insights into the load of transformers depending on their own losses. Transformers are among the most common, but important elements of the transmission and distribution networks. This is a reliable device with a guaranteed lifetime at the level of 25 to 30 years. New materials and new technologies for the production of transformers are leading to significantly reduce their own losses. Loss of transformers can be further influenced by both the change in their load and the flow of reactive power over transformers. Managing the overflow of reactive power through the transformers can then also influence the voltage conditions in the network.

Robust, fast and flexible symmetry plane detection based on differentiable symmetry measure

Abstract: Reflectional symmetry is a potentially very useful feature which many real-world objects exhibit. It is instrumental in a variety of applications such as object alignment, compression, symmetrical editing or reconstruction of incomplete objects. In this paper, we propose a novel differentiable symmetry measure, which allows using gradient-based optimization to find symmetry in geometric objects. We further propose a new method for symmetry plane detection in 3D objects based on this idea. The method performs well on perfectly as well as approximately symmetrical objects, it is robust to noise and to missing parts. Furthermore, it works on discrete point sets and therefore puts virtually no constraints on the input data. Due to flexibility of the symmetry measure, the method is also easily extensible, e.g., by adding more information about the input object and using it to further improve its performance. The proposed method was tested with very good results on many objects, including incomplete objects and noisy objects, and was compared to other state-of-the-art methods which it outperformed in most aspects.

Plane Space Representation in Context of Mode-Based Symmetry Plane Detection.

Abstract: This paper describes various representations of the space of planes. The main focus is on the plane space representation in the symmetry plane detection in \(E^3\) where many candidate planes for many pairs of points of the given object are created and then the most often candidate is found as a mode in the candidate space, so-called Mode-based approach. The result depends on the representation used in the mode-seeking process. The most important aspect is how well distances in the space correspond to similarities of the actual planes with respect to the input object. So, we describe various usable distance functions and compare them both theoretically and practically. The results suggest that, when using the Mode-based approach, representing planes by reflection transformations is the best way but other simpler representations are applicable as well. On the other hand, representations using 3D dual spaces are not very appropriate. Furthermore, we introduce a novel way of representing the reflection transformations using dual quaternions.

Robust, fast and flexible symmetry plane detection based on differentiable symmetry measure

Abstract: Reflectional symmetry is a potentially very useful feature which many real-world objects exhibit. It is instrumental in a variety of applications such as object alignment, compression, symmetrical editing or reconstruction of incomplete objects. In this paper, we propose a novel differentiable symmetry measure, which allows using gradient-based optimization to find symmetry in geometric objects. We further propose a new method for symmetry plane detection in 3D objects based on this idea. The method performs well on perfectly as well as approximately symmetrical objects, it is robust to noise and to missing parts. Furthermore, it works on discrete point sets and therefore puts virtually no constraints on the input data. Due to flexibility of the symmetry measure, the method is also easily extensible, e.g., by adding more information about the input object and using it to further improve its performance. The proposed method was tested with very good results on many objects, including incomplete objects and noisy objects, and was compared to other state-of-the-art methods which it outperformed in most aspects.

Combining Appearance and Gradient Information for Image Symmetry Detection

Abstract: This work addresses the challenging problem of reflection symmetry detection in unconstrained environments. Starting from the understanding on how the visual cortex manages planar symmetry detection, it is proposed to treat the problem in two stages: i) the design of a stable metric that extracts subsets of consistently oriented candidate segments, whenever the underlying 2D signal appearance exhibits definite near symmetric correspondences; ii) the ranking of such segments on the basis of the surrounding gradient orientation specularity, in order to reflect real symmetric object boundaries. Since these operations are related to the way the human brain performs planar symmetry detection, a better correspondence can be established between the outcomes of the proposed algorithm and a human-constructed ground truth. When compared to the testing sets used in recent symmetry detection competitions, a remarkable performance gain can be observed. In additional, further validation has been achieved by conducting perceptual validation experiments with users on a newly built dataset.

Plane Space Representation in Context of Mode-Based Symmetry Plane Detection.

Abstract: This paper describes various representations of the space of planes. The main focus is on the plane space representation in the symmetry plane detection in \(E^3\) where many candidate planes for many pairs of points of the given object are created and then the most often candidate is found as a mode in the candidate space, so-called Mode-based approach. The result depends on the representation used in the mode-seeking process. The most important aspect is how well distances in the space correspond to similarities of the actual planes with respect to the input object. So, we describe various usable distance functions and compare them both theoretically and practically. The results suggest that, when using the Mode-based approach, representing planes by reflection transformations is the best way but other simpler representations are applicable as well. On the other hand, representations using 3D dual spaces are not very appropriate. Furthermore, we introduce a novel way of representing the reflection transformations using dual quaternions.

Comparing Direct Measurements and Three-Dimensional (3D) Scans for Evaluating Facial Soft Tissue

Abstract: The inspection of patients’ soft tissues and the effects of various dental procedures on their facial physiognomy are quite challenging. To minimise discomfort and simplify the process of manual measuring, we performed facial scanning and computer measurement of experimentally determined demarcation lines. Images were acquired using a low-cost 3D scanner. Two consecutive scans were obtained from 39 participants, to test the scanner repeatability. An additional ten persons were scanned before and after forward movement of the mandible (predicted treatment outcome). Sensor technology that combines red, green, and blue (RGB) data with depth information (RGBD) integration was used for merging frames into a 3D object. For proper comparison, the resulting images were registered together, which was performed with ICP (Iterative Closest Point)-based techniques. Measurements on 3D images were performed using the exact distance algorithm. One operator measured the same demarcation lines directly on participants; repeatability was tested (intra-class correlations). The results showed that the 3D face scans were reproducible with high accuracy (mean difference between repeated scans <1%); the actual measurements were repeatable to some extent (excellent only for the tragus-pogonion demarcation line); computational measurements were accurate, repeatable, and comparable to the actual measurements. Three dimensional (3D) facial scans can be used as a faster, more comfortable for patients, and more accurate technique to detect and quantify changes in facial soft tissue resulting from various dental procedures.

As-rigid-as-possible volume tracking for time-varying surfaces

Abstract: Surfaces evolving through time are hard to analyze without prior knowledge of the represented deforming shape. Topological noise introduced by inaccuracies during surface capture and reconstruction renders the estimation of time-consistent correspondence an ill-posed problem. It has previously been shown that this problem may be mitigated by tracking the volume within the surface rather than the surface itself. Assuming that the captured phenomenon does not involve sudden appearance or disappearance of volume, it is possible to establish a bijective correspondence of volume elements, which in turn may be used for various purposes, such as extracting a canonical shape and guiding the computation of surface correspondence. In this paper, we discuss an improved volume tracking methodology that provides better results by modifying the energy formulation and by incorporating a notion of volume element affinity, combined with an improved optimization strategy. We also discuss two metrics that, when combined, quantify the quality of the tracking results.