Abstract Ground point filtering on national-level datasets is a challenge due to the presence of multiple types of landscapes. This limitation does not simply affect to individual users, but it is in particular relevant for those national institutions in charge of providing national-level Light Detection and Ranging (LiDAR) point clouds. Each type of landscape is typically better filtered by different filtering algorithms or parameters; therefore, in order to get the best quality classification, the LiDAR point cloud should be divided by the landscape before running the filtering algorithms. Despite the fact that the manual segmentation and identification of the landscapes can be very time intensive, only few studies have addressed this issue. In this work, we present a multistage approach to automate the identification of the type of landscape using several metrics extracted from the LiDAR point cloud, matching the best filtering algorithms in each type of landscape. An additional contribution is presented, a parallel implementation for distributed memory systems, using Apache Spark, that can achieve up to $$34\times$$ 34 × of speedup using 12 compute nodes.

GPU-embedded systems have gained popularity across various domains due to their efficient power consumption. However, in order to meet the demands of real-time or time-consuming applications running on these systems, it is crucial for them to be tuned to exhibit high performance. This paper addresses the issue by developing and comparing two tuning methodologies on GPU-embedded systems, and also provides performance insights for developers and researchers seeking to optimize applications running on these architectures. We focus on parallel prefix operations, such as FFT, scan primitives, and tridiagonal system solvers, which are performance-critical components in many applications. The study introduces an analytical model-driven tuning methodology and a Machine Learning (ML)-based tuning methodology. We evaluate the performance of the two tuning methodologies for different parallel prefix implementations of the BPLG library in an NVIDIA Jetson system, and compare their performance to the ones achieved through an exhaustive search. The findings shed light on the best strategies for handling the open challenge of performance portability for major computational patterns among server and embedded devices, providing practical guidance for offline and online tuning. We also address the existing gap in performance studies for parallel computational patterns in GPU-embedded systems by comparing the BPLG performance against other state-of-the-art libraries, including CUSPARSE, CUB, and CUFFT.

Abstract Due to the increasingly large amount of data acquired into point clouds, from LiDAR (Light Detection and Ranging) sensors and 2D/3D sensors, massive point clouds processing has become a topic with high interest for several fields. Current client-server applications usually use multiresolution out-of-core proposals; nevertheless, the construction of the data structures required is very time-consuming. Furthermore, these multiresolution approaches present problems regarding point density changes between different levels of detail and artifacts due to the rendering of elements entering and leaving the field of view. We present an autotuning multiresolution out-of-core strategy to avoid these problems. Other objectives are reducing loading times while maintaining low memory requirements, high visualization quality and achieving interactive visualization of massive point clouds. This strategy identifies certain parameters, called performance parameters, and defines a set of premises to obtain the goals mentioned above. The optimal parameter values depend on the number of points per cell in the multiresolution structure. We test our proposal in our web-based visualization software designed to work with the structures and storage format used and display massive point clouds achieving interactive visualization of point clouds with more than 27 billion points.

Abstract Land consolidation is an essential tool for public administrations to reduce the fragmentation of land ownership. In particular, parcel exchange shows promising potential for restructuring parcel holdings, even more when the number of parcels and owners involved is large. Unfortunately, the number of possible exchange combinations grows very quickly with the number of participating landowners and parcels, with the associated challenge of finding an acceptable solution. In this paper, we present a high-performance solution for parcel exchange based on genetic algorithms. Our proposal, using Apache Spark framework, is based on the exploiting of distributed-memory systems with effortless access in order to reduce the execution time. This also allows increasing the search width through multiple populations that share their advances. This can be achieved without compromising the search depth thanks to the higher amount of resources available from using distributed-memory systems. Our proposal is capable of achieving better solutions in lower amounts of time compared to previous works, showing that genetic algorithms on a high performance system can be used to propose fair parcel exchanges under strict time constraints, even in complex scenarios. The performance achieved allows for fast trial of several options, reducing the time usually needed to perform administrative procedures associated with land fragmentation problems. Specifically, our proposal is capable of combining the benefits of both depth-focused and width-focused multithreaded parallelization. It matches the speedup gains of depth-focused multithreaded parallelization. The width-focused parallelization provides local minimum resilience and fitness value reduction potential. In this paper, multithreading solutions and Spark-based solutions are tested.

In recent years, the evolution and improvement of LiDAR (Light Detection and Ranging) hardware has increased the quality and quantity of the gathered data, making the storage, processing and management thereof particularly challenging. In this work we present a novel, multi-resolution, out-of-core technique, used for web-based visualization and implemented through a non-redundant, data point organization method, which we call Hierarchically Layered Tiles (HLT), and a tree-like structure called Tile Grid Partitioning Tree (TGPT). The design of these elements is mainly focused on attaining very low levels of memory consumption, disk storage usage and network traffic on both, client and server-side, while delivering high-performance interactive visualization of massive LiDAR point clouds (up to 28 billion points) on multiplatform environments (mobile devices or desktop computers). HLT and TGPT were incorporated and tested in ViLMA (Visualization for LiDAR data using a Multi-resolution Approach), our own web-based visualization software specially designed to work with massive LiDAR point clouds.

Solving tridiagonal linear-equation systems is a fundamental computing kernel in a wide range of scientific and engineering applications, and its computation can be modeled with parallel algorithms. These parallel solvers are typically designed to compute problems whose data fit in a common shared-memory space where all the cores taking part in the computation have access. However, when the problem size is large, data cannot be entirely stored in the common shared-memory space, and a high number of high-latency communications are performed. One alternative is to partition the problem among different memory spaces. At this point, conventional parallel algorithms do not facilitate the partition of computation in independent tiles, since each reduction depends on equations that may be in different tiles. This article proposes an algorithm based on a tree reduction, called the Tree Partitioning Reduction (TPR) method, which partitions the problem into independent slices that can be partially computed in parallel within different common shared-memory spaces. The TPR method can be implemented for any parallel and distributed programming paradigm. Furthermore, in this work, TPR is efficiently implemented for CUDA GPUs to solve large size problems, providing highly competitive performance results with respect to existing packages, being, on average, 22.03× faster than CUSPARSE.

Big data technologies have been growing up quickly during past years. New storage and computing solutions appear while those already established in the market are improved with new features and better performance. Along with this growth also rises the number of applications and fields where the inclusion of big data technologies provides a large number of benefits, from the reduction in computational costs and economic resources to the improvement in the quality of the services provided which has a direct impact on the customers satisfaction. LiDAR (Light Detection and Ranging) data processing is one of the topics that could benefit from the adoption of these kind of technologies due to the massive datasets that are being gathered nowadays, with applications in archaeology, geography, geology or forestry, among many others. An efficient management of this volume of data becomes a key point especially in visualization, computing and analytic processes. In this paper, we analyse how web applications for the visualization of LiDAR data can benefit from the adoption of big data storage technologies, as well as the advantages and disadvantages that may determine the choice of one of them.

GPUs fulfill high computation demands, but it is necessary to develop code carefully, selecting algorithms well suited to the GPU architecture and applying different optimizations. This article presents a GPU-suitable algorithm and a tuning strategy for performing the scan primitive over large problem sizes in CUDA. This tuning strategy defines different performance premises to find the GPU execution parameters that maximize performance. Taking these premises into consideration, we easily develop the kernels using CUDA skeletons to ensure efficiency and portability. Based on this, we describe an optimal proposal analyzed over different multiple GPU environments, the first multiple-GPU batch scan proposal to the best of our knowledge. The resulting implementations outperform other well-known libraries in most cases, such as CUDPP, ModernGPU, Thrust, CUB and LightScan.

This work describes an efficient implementation for solving tridiagonal systems on Graphics Processing Units (GPUs). The Wang and Mou algorithm has a computation and communication pattern that matches very well to the GPU features. Thus, an implementation of this algorithm is presented here for solving large problem sizes, i.e., larger than CUDA GPU's shared memory capacity, in a Multiple-GPU environment. Also, small and medium problem sizes can take advantage of this implementation. Finally, this proposal has been tuned in order to obtain the maximum performance, resulting in a compact implementation that outperforms the CUSPARSE library (6.33x).

Current Graphics Processing Units (GPUs) are capable of obtaining high computational performance in scientific applications. Nevertheless, programmers have to use suitable parallel algorithms for these architectures and usually have to consider optimization techniques in the implementation in order to achieve said performance. There are many efficient proposals for limited-size problems which fit directly in the shared memory of CUDA GPUs, however, there are few GPU proposals that tackle the design of efficient algorithms for large problem sizes that exceed shared memory storage capacity. In this work, we present a tuning strategy that addresses this problem for some parallel prefix algorithms that can be represented according to a set of common permutations of the digits of each of its element indices [1], denoted as Index-Digit (ID) algorithms. Specifically, our strategy has been applied to develop flexible Multi-Stage (MS) algorithms for the Fast Fourier Transform (FFT) algorithm (MS-ID-FFT) and a tridiagonal system solver (MS-ID-TS) on the GPU. The resulting implementation is compact and outperforms other well-known and commonly used state-of-the-art libraries, with an improvement of up to 1.47x with respect to NVIDIA's complex CUFFT, and up to 33.2x in comparison with NVIDIA's CUSPARSE for real data tridiagonal systems.

Hybrid terrain models combine large regular data sets and high-resolution irregular meshes [triangulated irregular network (TIN)] for topographically and morphologically complex terrain features such as man-made microstructures or cliffs. In this paper, a new method to generate and visualize this kind of 3D hybrid terrain models is presented. This method can integrate geographic data sets from multiple sources without a remeshing process to combine the heterogeneous data of the different models. At the same time, the original data sets are preserved without modification, and, thus, TIN meshes can be easily edited and replaced, among other features. Specifically, our approach is based on the utilization of the external edges of convexified TINs as the fundamental primitive to tessellate the space between both types of meshes. Our proposal is eminently parallel, requires only a minimal preprocessing phase, and minimizes the storage requirements when compared with the previous proposals.

Modern graphics processing units (GPUs) offer very high computing power at relatively low cost. Nevertheless, designing efficient algorithms for the GPUs normally requires additional time and effort, even for experienced programmers. In this work we present a tuning methodology that allows the design for CUDA-enabled GPU architectures of index-digit algorithms, that is, algorithms where the data movement can be described as the permutations of the digits comprising the indices of the data elements. This methodology, based on two-stages identified as GPU resource analysis and operators string manipulation, is applied to FFT and tridiagonal systems solver algorithms, analyzing the performance features and the most adequate solutions. The resulting implementation is compact and outperforms other well-known and commonly used state-of-the-art libraries, with an improvement of up to 19.2 percent over NVIDIA's complex CUFFT , and more than 3000 percent over the NVIDIA'sCUDPP for real data tridiagonal systems.

Modern GPUs (Graphics Processing Units) offer very high computing power at relatively low cost. Nevertheless, designing efficient algorithms for the GPUs usually requires additional time and effort, even for experienced programmers. On the other hand, tridiagonal systems solvers are an important building block for a wide range of applications. In this paper, we present a new tuning parallel proposal in order to generate new tridiagonal systems solvers. This proposal is based on the combination of a new reduction algorithm (Redundant Reduction-RR) with a tuning proposal to generate efficient parallel prefix algorithms on the GPU. Specifically, we present two new solvers combining RR with two GPU efficient parallel prefix patterns. The performance of the resulting proposals was analyzed using three different CUDA GPUs, obtaining an improvement of up to 20.5x over the CUSPARSE library and 28.9x over CUDPP.

Current GPUs (Graphics Processing Units) offer high computational power at relatively low cost, nonetheless, this enhanced performance often comes at the expenses of flexibility and code complexity. Efficient GPU programming requires detailed knowledge on certain hardware aspects. The scan operator is an important building block for a wide range of algorithms. In this paper, we present a number of parallel scan methods based on the traditional cyclic reduction tridiagonal solver and the Ladner-Fischer parallel prefix adder. Futhermore, we analyze a set of new features introduced in the Kepler Nvidia architecture such as read-only data cache and shuffle instructions. Our methods provide an excellent performance in many cases, up to 48% improvement over the CUDA Data Parallel Primitives (CUDPP) library.

In order to increase the efficiency of existing software many works are incorporating GPU processing. However, despite the current advances in GPU languages and tools, taking advantage of their parallel architecture is still far more complex than programming standard multi-core CPUs. Performance profiling and analysis of known applications provides a useful insight of the hardware architecture and memory hierarchy. Afterwards, this analysis can be used to identify potential bottlenecks and tune other software so it can make a more efficient usage of the available resources. In this work we implement a small signal processing library which will be used to characterize the performance of most recent NVIDIA GPU architectures. The methodology used in our signal processing library is based on a series of building blocks that enable us to easily design several well-known algorithms with little effort. The library was built paying special attention to flexibility and adaptability. In this work we also show how a generic approach can be used to easily design these GPU algorithms while obtaining competitive performance, which results specially interesting from the productivity standpoint.

In this paper, we present a meshing scheme for the implementation of an adaptive tessellation of triangular meshes on the graphics processing unit (GPU). Tessellation is performed according to a local test to generate primitives dynamically. The refinement procedure does not require the pre-computation of any refinement pattern. The resulting adaptive procedure is efficient and simple, and generates the tessellation pattern of each triangle dynamically. The non-recursive strategy simplifies mesh reconstruction, avoids irregular memory access patterns and uses a simple control flow to make it a good candidate to guide the evolution of tessellation algorithms on future graphics cards. To test our proposal, we have used the geometry shader of current GPUs to generate primitives dynamically.

SUMMARY This special issue contributes to this promising field with extended and carefully reviewed versions of selected papers from two workshops, namely the 2nd Minisymposium on GPU Computing, which was held as part of the 9th International Conference on Parallel Processing and Applied Mathematics (PPAM 2011) in Torun (Poland); and the Workshop on Exploitation of Hardware Accelerators (WEHA 2011), which was held in conjunction with The 2011 International Conference on High Performance Computing & Simulation in Istanbul (Turkey). Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY This work presents cost‐effective multi‐graphics processing unit (GPU) parallel implementations of a finite‐volume numerical scheme for solving pollutant transport problems in bidimensional domains. The fluid is modeled by 2D shallow‐water equations, whereas the transport of pollutant is modeled by a transport equation. The 2D domain is discretized using a first‐order Roe finite‐volume scheme. Specifically, this paper presents multi‐GPU implementations of both a solution that exploits recomputation on the GPU and an optimized solution that is based on a ghost cell decoupling approach. Our multi‐GPU implementations have been optimized using nonblocking communications, overlapping communications and computations and the application of ghost cell expansion to minimize communications. The fastest one reached a speedup of 78 × using four GPUs on an InfiniBand network with respect to a parallel execution on a multicore CPU with six cores and two‐way hyperthreading per core. Such performance, measured using a realistic problem, enabled the calculation of solutions not only in real time but also in orders of magnitude faster than the simulated time.Copyright © 2012 John Wiley & Sons, Ltd.

Hybrid terrains are a convenient approach for the representation of digital terrain models, integrating heterogeneous data from different sources. In this article, we present a general, efficient scheme for achieving interactive level-of-detail rendering of hybrid terrain models, without the need for a costly preprocessing or resampling of the original data. The presented method works with hybrid digital terrains combining regular grid data and local high-resolution triangulated irregular networks. Since grid and triangulated irregular network data may belong to different datasets, a straightforward combination of both geometries would lead to meshes with holes and overlapping triangles. Our method generates a single multiresolution model integrating the different parts in a coherent way, by performing an adaptive tessellation of the region between their boundaries. Hence, our solution is one of the few existing approaches for integrating different multiresolution algorithms within the same terrain model, achieving a simple interactive rendering of complex hybrid terrains.

Fast Fourier Transform (FFT) is a useful tool for applications requiring signal analysis and processing. However, its high computational cost requires efficient implementations, specially if real time applications are used, where response time is a decisive factor. Thus, the computational cost and wide application range that requires FFT transforms has motivated the research of efficient implementations. Recently, GPU computing is becoming more and more relevant because of their high computational power and low cost, but due to its novelty there is some lack of tools and libraries. In this paper we propose an efficient implementation of the FFT with AMD's Brook+ language. We describe several features and optimization strategies, analyzing the scalability and performance compared to other well-known existing solutions.

The hierarchical radiosity algorithm provides high-quality illumination and the view-independent results obtained can be re-employed for different camera positions. On the other hand, the utilization of multiresolution models is a common solution for the real-time rendering of complex scenes. In this case, the level of detail of each object depends on the specific camera position. Unfortunately, global illumination computations may present an important performance loss in this context. In this paper we present a new solution for hierarchical radiosity for multiresolution systems. Our proposal is based on the application of an enriched hierarchical radiosity algorithm to an input scene with low-resolution objects (represented by coarse meshes) and the efficient data management of the resulting values. The representation of the information we use permits the application of the radiosity values obtained for the coarse version of an object to finer resolution versions of that object. Results of our implementation show that our algorithm produces high-quality images with an important reduction in computational costs.

Physically-based illumination is an essential factor for realistic rendering. In this context, hierarchical radiosity is one of the most accurate global illumination methods. One of the key features of the radiosity approach is that it obtains view-independent global illumination results. Unfortunately, global illumination has high computational and memory requirements, and hierarchical radiosity, though more efficient than other radiosity solutions, is not an exception. The progressive popularization of multiprocessor and multi-core processor systems makes the design and implementation of efficient parallel algorithms an appealing alternative in this field. In this paper we present a novel parallel radiosity method addressing the hierarchical radiosity computation on current homogeneous multi-core environments. One of the main contributions of our work is the use of different tasks to exploit the independent interactions among the geometric elements in the scene. Our parallel solution leads to a versatile radiosity implementation that takes advantage of the multiple computational resources in the system, such as multi-core processors and SMT (Simultaneous Multithreading) capabilities. Good results in terms of performance have been achieved.

Nowadays, one of the most active areas of research in computer graphics is focused on improving the performance of global illumination methods. In this paper we present a new parallel method for hierarchical radiosity computation. Contrary to usual solutions in the literature our approach carries out an effective partitioning and distribution of the input geometry among the processors. Thus, the memory constraint is reduced when processing large scenes. The method presented in this paper also introduces a multi-thread scheduling to improve interaction between processors. This solution replaces the polling strategy usually used in parallel computing, when several independent tasks need to establish asynchronous communication. The great flexibility of our parallel implementation has been demonstrated by the good results achieved on a testbed with different computing systems and test scenes

The demand for high quality and speed in graphical representations of 3D scenes is continuously increasing. An important aspect of visual realism is real-time processing of transparent objects. In order to provide a realistic solution to be considered for future graphics cards, proposed extensions to the hardware need to be small. In this paper, we propose two new hardware oriented proposals for computing order independent transparency for any number of layers. The first proposal is based on the precomputation of the contribution factor of each element to the final colour of the pixel. This permits the evaluation of the transparent objects without requiring their previous sorting. The second proposal is based on the utilization of a pre-sorting stage so that the transparent objects are organized in a back to front order. In both proposals, time requirements are reduced with respect to previous solutions.

Point based rendering techniques have recently become a promising alternative for high quality rendering of complex scenes. In order to handle a high number of points, the current graphics cards structure has to be analyzed for efficient exploitation of the hardware resources available. In this context, the real time perspective projections become a challenge because of the reduced number of dividers available in the graphics cards and their recursive structure. In this paper, we present a point projection algorithm that avoids the division operations. The technique we propose is based on the identification of the candidate pixels on the screen, and the selection of the correct one through simple comparison operations. The simplicity of the algorithm we propose permits the utilization of different projection units operating in parallel. We also present a scheduling that permits the introduction and efficient exploitation of a pipelined system. The algorithm is regular, simple, and characterized by efficient data management so that the processing rate is directly associated with the number of projection units employed. As a result, real time performance for the projection operations, even for critical scenes, can be achieved.

This paper presents a general data-parallel formulation for a class of problems based on the divide and conquer strategy. A combination of three techniques—mapping vectors, index-digit permutations and space-filling curves—are used to reorganize the algorithmic dataflow, providing great flexibility to efficiently exploit data locality and to reduce and optimize communications. In addition, these techniques allow the easy translation of the reorganized dataflows into HPF (High Performance Fortran) constructs. Finally, experimental results on the Cray T3E validate our method.