Congruent Set Research Articles

A High-Speed and Computational Cost-Effective 3D Recognition Method With 2D-Edges-Based 4-Points Congruent Set Algorithm

A High-Speed and Computational Cost-Effective 3D Recognition Method With 2D-Edges-Based 4-Points Congruent Set Algorithm

A Fast Registration Method for MEMS LiDAR Point Cloud Based on Self-Adaptive Segmentation

The Micro-Electro-Mechanical System (MEMS) LiDAR point cloud in autonomous vehicles has a large deflection range, which results in slow registration speed and poor applicability. To maximize speed, an improved Normal Distribution Transform (NDT) method that integrates point cloud density features has been proposed. First, the point cloud is reduced using a modified voxel filter and a pass-through filter. Next, the Intrinsic Shape Signature (ISS) algorithm is utilized to analyze the point cloud features and extract key points; the Four-Point Congruent Set (4PCS) algorithm is then employed to calculate the initial pose under the constraints of the key point set to complete the coarse registration. Finally, the self-adaptive segmentation model is constructed by using a K-D tree to obtain the density features of key points, and the NDT algorithm is combined with this model to form an SSM-NDT algorithm, which is used for fine registration. Each algorithm was compared on the autonomous vehicle dataset PandaSet and actual collected datasets. The results show that the novel method increases the speed by at least 60% and takes into account good registration accuracy and strong anti-interference.

Efficient co-registration of UAV and ground LiDAR forest point clouds based on canopy shapes

• Time-efficient co-registration of UAV and ground LiDAR data is proposed for plantation forests. • Coarse alignment of forest point clouds is divided into ground alignment and canopy image matching. • Canopy images are matched by two pairs of canopy corner points and the canopy overlap rate. • The runtime of coarse alignment is less than 1 s for millions of forest points. Registration of unmanned aerial vehicle laser scanning (ULS) and ground light detection and ranging (LiDAR) point clouds in forests is critical to create a detailed representation of a forest structure and an accurate retrieval of forest parameters. However, tree occlusion poses challenges for those registration methods used artificial markers, and some automated registration methods have low time-efficiency due to the process of object (e.g., tree, crown) segmentation. In this study, we propose an automated and time-efficient method to register ULS and ground LiDAR (including terrestrial and backpack laser scanning) forest point clouds. Registration involves coarse alignment and fine registration, where the coarse alignment is divided into vertical and horizontal alignment. The vertical alignment is implemented by rotating grounds to the horizontal plane, and the horizontal alignment is achieved by canopy image matching. During image matching, vegetation points are projected onto the horizontal plane to obtain two binary images, and then, canopy shape feature, which is described by a two-point congruent set and canopy overlap, is used to match the binary images. Finally, we implement coarse alignment of ULS and ground LiDAR datasets by combining the results of ground alignment and image matching and finish fine registration in six plantation forest plots with sizes of 0.03 ha to 0.25 ha. Experimental results show that the ULS and ground LiDAR data in different plots are registered, of which the coarse alignment errors are less than 0.20 m in the horizontal direction, the final registration accuracy is less than 0.15 m, and the average runtime is less than 1 s. Our study demonstrates the effectiveness of the proposed strategy and has able to perform accurate and quick registration of ULS and ground LiDAR data from plantation forests with different attributes.

Enhanced Super4PCS Algorithm by Comparing Transformed Normals at Corresponding Points.

In this paper, an enhanced algorithm based on the Super4PCS algorithm was established to address the problem of prolonged congruent set verification of Super4PCS for point clouds with many points or low overlap. By comparing normals of corresponding points in a source point cloud and a tentatively transformed target point cloud, this approach dramatically decreases the time required for candidate transformation verification. This strategy has been shown to improve registration efficiency in experiments.

Voxel Grid-Based Fast Registration of Terrestrial Point Cloud

Terrestrial laser scanning (TLS) is an important part of urban reconstruction and terrain surveying. In TLS applications, 4-point congruent set (4PCS) technology is widely used for the global registration of point clouds. However, TLS point clouds usually enjoy enormous data and uneven density. Obtaining the congruent set of tuples in a large point cloud scene can be challenging. To address this concern, we propose a registration method based on the voxel grid of the point cloud in this paper. First, we establish a voxel grid structure and index structure for the point cloud and eliminate uneven point cloud density. Then, based on the point cloud distribution in the voxel grid, keypoints are calculated to represent the entire point cloud. Fast query of voxel grids is used to restrict the selection of calculation points and filter out 4-point tuples on the same surface to reduce ambiguity in building registration. Finally, the voxel grid is used in our proposed approach to perform random queries of the array. Using different indoor and outdoor data to compare our proposed approach with other 4-point congruent set methods, according to the experimental results, in terms of registration efficiency, the proposed method is more than 50% higher than K4PCS and 78% higher than Super4PCS.

Pairwise Coarse Registration of Indoor Point Clouds Using 2D Line Features

Registration is essential for terrestrial LiDAR (light detection and ranging) scanning point clouds. The registration of indoor point clouds is especially challenging due to the occlusion and self-similarity of indoor structures. This paper proposes a 4 degrees of freedom (4DOF) coarse registration method that fully takes advantage of the knowledge that the equipment is levelled or the inclination compensated for by a tilt sensor in data acquisition. The method decomposes the 4DOF registration problem into two parts: (1) horizontal alignment using ortho-projected images and (2) vertical alignment. The ortho-projected images are generated using points between the floor and ceiling, and the horizontal alignment is achieved by the matching of the source and target ortho-projected images using the 2D line features detected from them. The vertical alignment is achieved by making the height of the floor and ceiling in the source and target points equivalent. Two datasets, one with five stations and the other with 20 stations, were used to evaluate the performance of the proposed method. The experimental results showed that the proposed method achieved 80% and 63% successful registration rates (SRRs) in a simple scene and a challenging scene, respectively. The SRR in the simple scene is only lower than that of the keypoint-based four-point congruent set (K4PCS) method. The SRR in the challenging scene is better than all five comparison methods. Even though the proposed method still has some limitations, the proposed method provides an alternative to solve the indoor point cloud registration problem.

Automated Measurement of Heart Girth for Pigs Using Two Kinect Depth Sensors.

The heart girth parameter is an important indicator reflecting the growth and development of pigs that provides critical guidance for the optimization of healthy pig breeding. To overcome the heavy workloads and poor adaptability of traditional measurement methods currently used in pig breeding, this paper proposes an automated pig heart girth measurement method using two Kinect depth sensors. First, a two-view pig depth image acquisition platform is established for data collection; the two-view point clouds after preprocessing are registered and fused by feature-based improved 4-Point Congruent Set (4PCS) method. Second, the fused point cloud is pose-normalized, and the axillary contour is used to automatically extract the heart girth measurement point. Finally, this point is taken as the starting point to intercept the circumferential perpendicular to the ground from the pig point cloud, and the complete heart girth point cloud is obtained by mirror symmetry. The heart girth is measured along this point cloud using the shortest path method. Using the proposed method, experiments were conducted on two-view data from 26 live pigs. The results showed that the heart girth measurement absolute errors were all less than 4.19 cm, and the average relative error was 2.14%, which indicating a high accuracy and efficiency of this method.

Availability of Recently Described Ptychadena (Anura: Ptychadenidae) Nomina from Ethiopia.

Frogs of the genus Ptychadena (Boulenger, 1917) have long been identified as harboring cryptic diversity and comprising numerous species-complexes (Largen 1997; Zimkus et al. 2017), and many authors have recognized the particularly high hidden richness in the Ethiopian highlands (Largen 1997; see Largen Spawls 2010 and refs. within). This cryptic diversity was confirmed by recent molecular studies (Freilich et al. 2014; Smith et al. 2017a, Reyes-Velasco et al. 2018). Those authors identified a congruent set of evolutionarily distinct candidate species using both mitochondrial and nuclear DNA, and described the geographic and ecological isolation of these species in detail (Freilich et al. 2014; Smith et al. 2017a).

A Methodology to Estimate Net Proton: Phosphorus Co-Adsorption Ratios for Acidic Soils

Despite extensive research, the behaviour of the key nutrient element, phosphorus (P), in soil is not yet fully understood. This study focussed on the outstanding issue of the co-adsorption of protons (H+) and P by soils. We developed a congruent set of measures to determine the net H+:P co-adsorption ratio and tested it on goethite, for which a ratio of 1.6:1 had been estimated under CO2-free conditions for additions of NaH2PO4. Under our conditions, and using additions of KH2PO4, the net H+:P co-adsorption ratio was estimated to be 1.44:1, i.e., in passable agreement with the published value. Application of the protocol to acidic soils resulted in a net H+:P co-adsorption ratio of 1.92:1, and substitution of H3PO4 for KH2PO4 gave a ratio of 1.96:1. These ratios for soils differ significantly from that for goethite. The soils for which we estimated net H+:P co-adsorption ratios had a wide range of properties and two had received previous applications of P fertiliser (Ca(H2PO4)2), which does not appear to have affected the net H+:P co-adsorption ratios. The H+:P co-adsorption ratio method could benefit from refinement, and further study is required to explore how these findings may apply to commercial P fertilisers under field conditions.

Registration of Terrestrial Laser Scanning Surveys Using Terrain-Invariant Regions for Measuring Exploitative Volumes over Open-Pit Mines

Terrestrial laser scanning (TLS) techniques have been widely used in open-pit mine applications. It is a crucial task to measure the exploitative volume of open-pit mines, within a specific time interval. One major challenge is posed, however, when conducting accurate registrations for temporal TLS surveys in continuously changing areas, created by excavation activities. In this paper, we propose a coarse-to-fine registration method, based on terrain-invariant regions (TIR), for temporal TLS surveys. More specifically, an approximate four-point congruent set (4PCS) of temporal TLS surveys is first identified, based on affine invariant rules. Second, a set of correspondences among temporal TLS surveys were collected by matching multi-scale sparse features of the 3D neighbors, centered at the approximate 4PCS. Third, the correspondences were used to estimate a rigid motion between the overlapping TLS surveys for the coarse registration, according to which the initial TIR from temporal TLS surveys were identified. Finally, the rigid motion between temporal TLS was iteratively optimized, based on the point clouds, only from the TIR. Based on the fine-level registered TLS surveys, Digital Elevation Models (DEMs) can be generated to calculate the exploitative volume, through a DEM differential. We applied the proposed method to two open-pit mines in China, and also compared our method with five state-of-the-art methods for registering temporal TLS surveys. Experimental results indicated that the proposed method achieved a higher registration accuracy than the state-of-the-art methods. Based on the registered result, our method achieved a 98.03% overall accuracy for measuring the exploitative volume, compared to in-situ measurement.

Multiscale Sparse Features Embedded 4-Points Congruent Sets for Global Registration of TLS Point Clouds

The 4-points congruent sets (4PCS) techniques have widely been used for global registration of point clouds in terrestrial laser scanning (TLS) applications. Nevertheless, due to many 4PCS methods adopt a downsampling strategy in the collection of correspondences; it is challenging to obtain a real congruent set of tuples in different point clouds with varying density. This letter embeds multiscale sparse features (MSSF) into 4PCS to enable efficient global registration of TLS clouds. Specifically, multiscale clusters are used to extract point features, among which a sparse coding is performed to obtain the representative MSSF. The obtained MSSF are then embedded into the 4PCS variants, taking both geometrical structure and representative feature similarity into account when performing a four-point congruent tuples matching. Moreover, a normal constraint is considered in the selection of noncoplanar four-point bases rather than coplanar ones in the source cloud. This configuration decreases the number of four-point bases and thus improves the processing efficiency and registration accuracy. The proposed method was applied to two experiments with TLS point clouds from building and hillslope scenarios, respectively. In addition, the proposed MSSF configuration was embedded in two 4PCS variants, and compared with the original methods for global registration. The comparison shows evident improvements in terms of the registration accuracy and efficiency if our embedment is used.

Reassembling fractured sand particles using fracture-region matching algorithm

Characterizing the fracture surfaces within a single sand particle precisely and describing it quantitatively plays an essential role in understanding the breakage behavior of sands. This paper presents a novel method to obtain the realistic fracture surface from 3D particle fragment reassembly. Firstly, a few sets of 2D slices of a fractured particle were collected by using a self-designed mini-loading apparatus combined with the nano-focus X-ray computed tomography. Then the de-noising and watershed segmentation algorithms were applied to the 2D images before the reconstruction work which aimed to acquire 3D digital models of the broken fragments. After separating the 3D fractured particle into pieces, we used the minimum spanning tree to construct the feature curve networks of the fragments that has a higher curvature compared with other locations and to identify all simple chordless cycles in this feature curve networks. The Hausdorff distance and the modified 4-points congruent set algorithms were adopted to identify potential simple chordless cycles for matching and to match them. To avoid the substantial penetration effects, we used the ray-triangle intersection algorithm to detect whether the matched points are within triangulated volume or not. The matching result shows that the proposed method is capable of reassembling fractured particles and it will facilitate the better prediction of particle fracture in numerical modelling.

4-Plane congruent sets for automatic registration of as-is 3D point clouds with 3D BIM models

Abstract Construction quality and progress control are demanding, yet critical construction activities. Building Information Models and as-built scanned data can be used in Scan-vs-BIM processes to effectively and comprehensively support these activities. This however requires accurate registration of scanned point clouds with 3D (BIM) models. Automating such registration remains a challenge in the context of the built environment, because as-built can be incomplete and/or contain data from non-model objects, and construction buildings and other structures often present symmetries and self-similarities that are very challenging to registration. In this paper, we present a novel automatic coarse registration method that is an adaptation of the ‘4 Points Congruent Set’ algorithm to the use of planes; we call it the ‘4-Plane Congruent Set’ (4-PlCS) algorithm. The approach is further integrated in a software system that delivers not one but a ranked list of the most likely transformations, so to allow the user to quickly select the correct transformation, if need be. Two variants of the method are also considered, in particular one in the case when the vertical axis is known a priori; we call that method the 4.5-PlCS method. The proposed algorithm is tested using five different datasets, including three simulated and two real-life ones. The results show the effectiveness of the proposed method, where the correct transformation always ranks very high (in our experiments, first or second), and is extremely close to the ground-truth transformation. Experimental comparison of the proposed approach with a standard, more intuitive approach based on finding 3-plane congruent sets shows the discriminatory power of 4-plane bases over 3-plane bases, albeit at no clear benefits in terms of computational time. The experimental results for the 4.5-PlCS method show that it delivers a non-negligible reduction in computational time (approx. 20%), but at no additional benefit in terms of effectiveness in finding the correct transformation.

A G-Super4PCS Registration Method for Photogrammetric and TLS Data in Geology

Photogrammetry and Terrestrial laser scanning (TLS) are the two primary non-contact active measurement techniques in geology. Integrating TLS data with digital images may achieve complementary advantages of spatial information as well as spectrum information, which would be very valuable for automatic rock surface extraction. In order to extract accurate and comprehensive geological information with both digital images and TLS point cloud, the registration problem for different sensor sources should be solved first. This paper presents a Generalized Super 4-points Congruent Sets (G-Super4PCS) algorithm to register the TLS point cloud as well as Structure from Motion (SfM) point cloud generated from disordered digital images. The G-Super4PCS algorithm mainly includes three stages: (1) key-scale rough estimation for point clouds; (2) extraction for the generalized super 4-points congruent base set and scale adaptive optimization; and (3) fine registration with Iterative Closest Point (ICP) algorithm. The developed method was tested with the columnar basalt data acquired in Guabushan National Geopark in Jiangsu Province, China. The results indicate that the proposed method could be used for indirect registration between digital images and TLS point cloud, and the result of which would be prepared for further integration research.

Phylogenetic position of Geitleribactron purpureum (Synechococcales, Cyanobacteria / Cyanophyceae) and its implications for the taxonomy of Chamaesiphonaceae and Leptolyngbyaceae

Over the last decades, the taxonomy of cyanobacteria has been considerably improved and restructured due to the increase in data output from molecular phylogeny. Recently, a new protocol was developed that enables reliable sequencing of 16S rRNA genes in cultivation-resistant cyanobacteria using analysis of single cells, filaments, or colonies. In the current study, we examined a sample of a heteropolar unicellular cyanobacterium, Geitleribactron purpureum, from the holotype material (deep epilithon of Lake Tovel, Western Dolomites, Italy). We isolated and purified single colonies of G. purpureum, and subjected them to direct PCR and 16S rRNA gene sequencing. We obtained a congruent set of sequences that formed a unique, isolated cyanobacterial lineage, showing phylogenetic clustering among simple filamentous genera of the family Leptolyngbyaceae. We provide evidence for deep polyphyly in Chamaesiphonaceae, and suggest that Geitleribactron should be re-classified in the Leptolyngbyaceae.

Congruence of decay chains of elements 113, 115, and 117

Superheavy element research relies heavily on the detection of correlated decay chains. When several chains have been detected, it is natural to ask whether they form one congruent set, or whether they should be further divided into subsets. To statistically assess the congruence between the chains in a data set, we developed a procedure to calculate a Figure-of-Merit for low-number statistics. In this work, the method is applied to the world data set of odd-Z superheavy nuclei with Z ≥ 113. Some of the postulated sets of chains are found to be congruent, while others are not. The findings are of relevance for the IUPAC and IUPAP approvals of the new elements Z = 113, 115, and 117.

Fully Automatic Registration of Image Sets on Approximate Geometry

The photorealistic acquisition of 3D objects often requires color information from digital photography to be mapped on the acquired geometry, in order to obtain a textured 3D model. This paper presents a novel fully automatic 2D/3D global registration pipeline consisting of several stages that simultaneously register the input image set on the corresponding 3D object. The first stage exploits Structure From Motion (SFM) on the image set in order to generate a sparse point cloud. During the second stage, this point cloud is aligned to the 3D object using an extension of the 4 Point Congruent Set (4PCS) algorithm for the alignment of range maps. The extension accounts for models with different scales and unknown regions of overlap. In the last processing stage a global refinement algorithm based on mutual information optimizes the color projection of the aligned photos on the 3D object, in order to obtain high quality textures. The proposed registration pipeline is general, capable of dealing with small and big objects of any shape, and robust. We present results from six real cases, evaluating the quality of the final colors mapped onto the 3D object. A comparison with a ground truth dataset is also presented.

Evolutionary method of construction of solutions of polynomials and related generalized dynamics

Invariant theory as a study of properties of polynomials under translational transformations is developed. Class of polynomials with congruent set of eigenvalues is introduced. Evolution equations for eigenvalues and coefficients remaining the polynomial within proper class of polynomials are formulated. The connection with equations for hyper-elliptic Weierstrass and hyper-elliptic Jacobian functions is found. Algorithm of calculation of eigenvalues of the polynomials based on the evolution process is elaborated. Elements of the generalized dynamics with n-order characteristic polynomials are built.

Improving land‐surface model hydrology: Is an explicit aquifer model better than a deeper soil profile?

We use Monte Carlo analysis to show that explicit representation of an aquifer within a land‐surface model (LSM) decreases the dependence of model performance on accurate selection of subsurface hydrologic parameters. Within the National Center for Atmospheric Research Community Land Model (CLM) we evaluate three parameterizations of vertical water flow: (1) a shallow soil profile that is characteristic of standard LSMs; (2) an extended soil profile that allows for greater variation in terrestrial water storage; and (3) a lumped, unconfined aquifer model coupled to the shallow soil profile. North American Land Data Assimilation System meteorological forcing data (1997–2005) drive the models as a single column representing Illinois, USA. The three versions of CLM are each run 22,500 times using a random sample of the parameter space for soil texture and key hydrologic parameters. Other parameters remain constant. Observation‐based monthly changes in state‐averaged terrestrial water storage (dTWS) are used to evaluate the model simulations. After single‐criteria parameter exploration, the schemes are equivalently adept at simulating dTWS. However, explicit representation of groundwater considerably decreases the sensitivity of modeled dTWS to errant parameter choices. We show that approximate knowledge of parameter values is not sufficient to guarantee realistic model performance: because interaction among parameters is significant, they must be prescribed as a congruent set.

Systematic review on embracing cultural diversity for developing and sustaining a healthy work environment in healthcare

Objectives The objective of this review was to evaluate evidence on the structures and processes that support development of effective culturally competent practices and a healthy work environment. Culturally competent practices are a congruent set of workforce behaviours, management practices and institutional policies within a practice setting resulting in an organisational environment that is inclusive of cultural and other forms of diversity. Inclusion criteria This review included quantitative and qualitative evidence, with a particular emphasis on identifying systematic reviews and randomised controlled trials. For quantitative evidence, other controlled, and descriptive designs were also included. For qualitative evidence, all methodologies were considered. Participants were staff, patients, and systems or policies that were involved or affected by concepts of cultural competence in the nursing workforce in a healthcare environment. Types of interventions included any strategy that had a cultural competence component, which influenced the work environment, and/or patient and nursing staff in the environment. The types of outcomes of interest to this review included nursing staff outcomes, patient outcomes, organisational outcomes and systems level outcomes. Search strategy The search sought both published and unpublished literature written in the English language. A comprehensive three-step search strategy was used, first to identify appropriate key words, second to combine all optimal key words into a comprehensive search strategy for each database and finally to review the reference lists of all included reviews and research reports. The databases searched were CINAHL, Medline, Current Contents, the Database of Abstracts of Reviews of Effectiveness, The Cochrane Library, PsycINFO, Embase, Sociological Abstracts, Econ lit, ABI/Inform, ERIC and PubMed. The search for unpublished literature used Dissertation Abstracts International. Methodological quality Methodological quality was independently established by two reviewers, using standardised techniques from the Joanna Briggs Institute (JBI) System for the Unified Management, Assessment and Review of Information (SUMARI) package. Discussion with a third reviewer was initiated where a low level of agreement was identified for a particular paper. Following inclusion, data extraction was conducted using standardised data extraction tools from the JBI SUMARI suite for quantitative and qualitative research. Data synthesis was performed using the JBI Qualitative Assessment and Review Instrument and JBI Narrative, Opinion and Text Assessment and Review Instrument software to aggregate findings by identifying commonalities across texts. Quantitative data were presented in narrative summary, as statistical pooling was not appropriate with the included studies. Results Of the 659 identified papers, 45 were selected for full paper retrieval, and 19 were considered to meet the inclusion criteria for this review. The results identified a number of processes that would contribute to the development of a culturally competent workforce. Appropriate and competent linguistic services, and intercultural staff training and education, were identified as key findings in this review. Conclusions The review recommends that health provider agencies establish links with organisations that can address needs of culturally diverse groups of patients, include cultural competence in decision support systems and staff education as well as embed them in patient brochures and educational materials. The review also concluded that staff in-service programs consider the skills needed to foster a culturally competent workforce, and recruitment strategies that also explicitly address this need.