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• 251.
Massachusetts General Hospital, Boston, MA.
Massachusetts General Hospital, Boston, MA. Umeå University, Faculty of Science and Technology, Department of Computing Science. Massachusetts General Hospital, Boston, MA.
Development of a Knee Phantom for the Evaluation of Methods for Measuring Knee Joint Kinematics2004In: Transactions of the Orthopaedics Research Society, ORS , 2004, Vol. 29, p. 1385-1385Conference paper (Other academic)
• 252.
Massachusetts General Hospital, Boston, MA.
Massachusetts General Hospital, Boston, MA. Massachusetts General Hospital, Boston, MA. Massachusetts General Hospital, Boston, MA. Sahlgrenska University Hospital. Umeå University, Faculty of Science and Technology, Department of Computing Science. Massachusetts General Hospital, Boston, MA. Massachusetts General Hospital, Boston, MA.
Experimental Assessment of Precision and Accuracy of Radiostereometric Analysis (RSA) for the Determination of Polyethylene Wear in a Total Hip Replacement Model2001In: Proceedings of the 11th annual meeting of AAKHS, AAKHS , 2001, p. 49-49Conference paper (Other academic)
• 253.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Pipelined Messaging Gateway2015Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis

The SMS gateway EMG uses separate threads for each connection. This requires a large number of locks to avoid data corruption, and causes problems when scaling to thousands of connections. The CPU load goes very high, and the amount of addressable memory per thread becomes low.

This report examines an alternative implementation, where each thread instead handles a separate part of the processing. The two architectures are compared based on throughput, resource utilisation, code complexity and more.

The results show what while throughput is about the same, the alternative implementation is better at keeping the CPU load within reasonable limits. However, it also requires more advanced data structure and algorithms to be efficient.

• 254.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Continuous Collision Detection for Wires with Adaptive Resolution2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

For interactive simulations using a physics engine, a fixed time step is often necessary in order to maintain real-time performance. Furthermore, collisions between the simulated geometric objects have to be detected by solving a computational problem called collision detection. In its discrete formulation, the geometric configurations of the bodies are evaluated at each simulation time step, whereas its continuous variant also considers the bodies’ motion in betweenthe time steps. A fixed simulation time step can lead to missed collisions if only discrete collision detection is performed. This problem arises especially when simulating thin objects such as wires, chains, or ropes for applications like heavy lifting or anchor handling. In order to be able to simulate wires interacting with each other in real-time simulations, continuous collision detection is therefore necessary.An existing simulation model for wires, chains, and ropes using adaptive wire resolution has been augmented using continuous collision detection. This addition has been integrated into the physics engine AGX Dynamics. Issues in existing methods for continuous collision detection of moving line segments caused by co-linearity and co-planarity have been identified, classified and addressed. Using this augmented approach to continuous collision detection allows for alarger fixed simulation step size compared to discrete collision detection, and thus decreases the total run time by up to 58.22% in relevant scenarios.

• 255.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
A design study on applications for mobile devices2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

The question of how we should develop mobile software is - with the proliferation of smartphones and HTML5 - an interesting and hot topic. This thesis introduces and compares the different approaches to mobile software development. It focuses on the basic web, native and hybrid approaches but also touches on cross platform tools. The aim of the thesis is to provide a solid understanding of the alternatives and help guide a potential choice between the techniques.

As a guide to making the decision this work is far from complete, it's a fast moving area with a lot of uncertainty and accounting for all (or even most) of the variables involved in the decision is next to impossible. The primary observation is that the native approach continues to dominate when it comes to user experience and functionality, but the other approaches have great potential and are improving at a fast pace. Costwise, native is often the inferior alternative, especially when targeting many platforms. As many existing resources, such as a website and web developers, can be used to make web or hybrid applications, the cost difference increases even more.

• 256. Breitgand, D.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Policy-Driven Service Placement Optimization in Federated Clouds2011Report (Other academic)

Efficient provisioning of elastic services constitutes a significant management challenge for cloud computing providers. We consider a federated cloud paradigm, where one cloud can subcontract workloads to partnering clouds to meet peaks in demand without costly over-provisioning. We propose a model for service placement in federated clouds to maximize profit while protecting Quality of Service (QoS) as specified in the Service Level Agreements (SLA) of the workloads. Our contributions include an Integer Linear Program (ILP) formulation of the generalized federated placement problem and application of this problem to load balancing and consolidation within a cloud, as well as for cost minimization for remote placement in partnering clouds. We also provide a 2-approximation algorithm based on a greedy rounding of a Linear Program (LP) relaxation of the problem. We implement our proposed approach in the context of the RESERVOIR architecture.

• 257.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Real-time DATMO Based on Deep 3D Point Cloud Features3D object detection in point cloud data2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Perception for autonomous drive systems is the most essential task for safe and reliable driving. LiDAR sensors can be used for this and are vying for being crowned as an essentia lelement in this task.In this thesis, we present a novel real-time solution for detection and tracking of moving objects which utilizes deep learning based 3D object detection. On one hand, we present YOLO++, a 3D object detection network on point clouds only. A network that expands YOLOv3, the latest contribution to standard real-time object detector for three channel images. YOLO++ extracts the standard YOLO’s predictions plus an angle and a height from projected point clouds. Our unified architecture is fast. It processes images in 20 frames per second. Our experiments on the KITTI benchmark suite show that we achieve state-of-the-art efficiency but with a mediocre accuracy for car detection comparable to the result of Tiny-YOLOv3 on the COCO dataset.On the other hand, we present a multi-threaded object tracking solution that makes use o fthe detected objects by YOLO++. Each observation is associated to a thread with a novel concurrent data association process where each of the threads contain an Extended Kalman Filter that is used for predicting and estimating the object’s state over time. Futhermore, a LiDAR odometry algorithm is used to obtain absolute information about the movement, since the movement of objects are inherently relative to the sensor perceiving them. We obtain 33 state updates per second with an equal amount of threads to the number of cores inour main workstation.Even if the joint solution has not been tested on a system with enough computational power it is ready for deployment. We expect it to be runtime constrained by the slowest subsystem which happens to be the object detection system. This satisfies our real-time constraint of 10 frames per second of our final system by a large margin. Finally, we show that our system can take advantage of the predicted semantic information from the Kalman Filters in order to enhance the inference process in our YOLO++ architecture.

• 258.
Swedish Defence Research Agency (FOI).
Umeå University, Faculty of Science and Technology, Department of Computing Science. Swedish Defence Research Agency (FOI). Swedish Defence Research Agency (FOI). Swedish Defence Research Agency (FOI).
Abstraction techniques for social networks2010In: Proceedings of the 2010 International Conference on Advances in Social Networks Analysis and Mining, IEEE, 2010Conference paper (Refereed)
• 259.
University of Bath.
Umeå University, Faculty of Science and Technology, Department of Computing Science. University of Bath, Bath, UK.
How society can maintain human-centric artificial intelligence2019In: Human-centered digitalization and services / [ed] Marja Toivonen and Eveliina Saari, Springer, 2019, p. 305-323Chapter in book (Refereed)

Although not a goal universally held, maintaining human-centric artificial intelligence is necessary for society's long-term stability. Fortunately, the legal and technological problems of maintaining control are actually fairly well understood and amenable to engineering. The real problem is establishing the social and political will for assigning and maintaining accountability for artifacts when these artifacts are generated or used. In this chapter we review the necessity and tractability of maintaining human control and the mechanisms by which such control can be achieved. What makes the problem both most interesting and most threatening is that achieving consensus around any human-centered approach requires at least some measure of agreement on broad existential concerns.

The full text will be freely available from 2021-06-04 11:17
• 260.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Computing network centrality measures on fMRI data using fully weighted adjacency matrices2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

A lot of interesting research is currently being done in the field of neuroscience, a recent subject being the effort to analyse the the human brain connectome and its functional connectivity. One way this is done is by applying graph-theory based network analysis, such as centrality, on data from fMRI measurements. This involves creating a graph representation from a correlation matrix containing the correlations over time between all measured voxels. Since the input data can be very big, this results in computations that are too memory and time consuming for an ordinary computer. Researchers have used different techniques to work around this problem, examples include thresholding correlations when creating the adjacency matrix and using a smaller input data with lower resolution.This thesis proposes three ways to compute two different centrality measures, degree centrality and eigenvector centrality, on fully weighted adjacency matrices that are built from complete correlation matrices computed from high resolution input data. The first is reducing the problem by doing the calculations in optimal order and avoiding the construction of the large correlation matrix. The second solution is to distribute and do the computations in parallel on a large computer cluster using MPI. The third solution is to calculate as large sets as possible on an ordinary laptop using shared-memory parallelism with OpenMP. Algorithms are presented for the different solutions, and the effectiveness of the implementations of them is tested.

• 261.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Automated software testing for cross-platform systems2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

SILK is the preferred audio codec to use in a call between Skype clients. Everytime the source code has been changed there is a risk the code is no longer bit-exact between all the dffierent platforms. The main task for this thesis is to make it possible to test bit-exactness between platforms automatically to save resources for the company.

During this thesis a literature study about software testing has been carried out to find a good way of testing bit-exactness between different platforms. The advantages and disadvantages with the different testing techniques was examined during this study.

The result of the thesis is a framework for testing bit-exactness between several different platforms. Based on the conclusions from the literature study the framework is using a technique called data-driven testing to carry out the bit-exactness tests on SILK.

• 262.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
JavaScript and Web Integration of AgX Multiphysics Engine2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

JavaScript is the de facto language for client-side scripting on the web and has in recent years received a great boost in performance thanks to the `browser wars' where the different browser vendors compete to get higher market shares. AgX is a physics engine developed by Algoryx in Umeå, intended for use in simulations. This thesis explores possible methods of integrating JavaScript with AgX and in extension the possibility of integrating AgX into the web browser as a plugin, effectively enabling AgX for use in different web applications. Efforts were made to combine the embedded JavaScript API with the AgX browser plugin. This was found to be unfeasible for different reasons, although the AgX plugin as a separate piece of software was shown to work well.

• 263.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Supporting Communication and Collaboration in the Process Automation Industry2011Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis

This thesis shows new domains for social media applications. More specifically, it explores how communication and collaboration can be supported in the process automation industry.´A concept demonstrator was implemented using the Sencha Touch framework. The prototype is based on several identified use cases, and has been tested and evaluated with end users.The design and functionality is inspired from social media applications such as Facebook and Stack Overow. These kinds of popular social media platforms have developed an intuitive way of structuring and grouping information. This report shows that these information structures are indeed applicable in non traditional domains, such as the process automation industry.The concept answers to identified problem scenarios, e.g., communicating information between shifts and support of handling alarms. It also approaches personalization in order to support users focus and interest.

• 264.
Department of Geography, University of Zurich, Switzerland.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Geography, University of Zurich, Switzerland.
Distributing Attention Between Environment and Navigation System to Increase Spatial Knowledge Acquisition During Assisted Wayfinding2018In: Proceedings of Workshops and Posters at the 13th International Conference on Spatial Information Theory (COSIT 2017) / [ed] Fogliaroni P., Ballatore A., Clementini E., Springer, 2018, p. 19-22Conference paper (Refereed)

Travelers happily follow the route instructions of their devices when navigating in an unknown environment. Navigation systems focus on route instructions to allow the user to efficiently reach a destination, but their increased use also has negative consequences. We argue that the limitation for spatial knowledge acquisition is grounded in the system’s design, primarily aimed at increasing navigation efficiency. Therefore, we empirically investigate how navigation systems could guide users’ attention to support spatial knowledge acquisition during efficient route following tasks.

• 265.
University of Zurich, Switzerland.
Umeå University, Faculty of Science and Technology, Department of Computing Science. University of Zurich, Switzerland.
How does navigation system behavior influence human behavior?2019In: Cognitive Research: Principles and Implications, E-ISSN 2365-7464, Vol. 4, no 5Article in journal (Refereed)

• 266.
Department of Mathematics, Faculty of Science, University of Zagreb, Zagreb, Croatia.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Institute of Mathematics, EPFL, Lausanne, Switzerland.
A Householder-Based Algorithm for Hessenberg-Triangular Reduction2018In: SIAM Journal on Matrix Analysis and Applications, ISSN 0895-4798, E-ISSN 1095-7162, Vol. 39, no 3, p. 1270-1294Article in journal (Refereed)

The QZ algorithm for computing eigenvalues and eigenvectors of a matrix pencil $A - \lambda B$ requires that the matrices first be reduced to Hessenberg-triangular (HT) form. The current method of choice for HT reduction relies entirely on Givens rotations regrouped and accumulated into small dense matrices which are subsequently applied using matrix multiplication routines. A nonvanishing fraction of the total flop-count must nevertheless still be performed as sequences of overlapping Givens rotations alternately applied from the left and from the right. The many data dependencies associated with this computational pattern leads to inefficient use of the processor and poor scalability. In this paper, we therefore introduce a fundamentally different approach that relies entirely on (large) Householder reflectors partially accumulated into block reflectors, by using (compact) WY representations. Even though the new algorithm requires more floating point operations than the state-of-the-art algorithm, extensive experiments on both real and synthetic data indicate that it is still competitive, even in a sequential setting. The new algorithm is conjectured to have better parallel scalability, an idea which is partially supported by early small-scale experiments using multithreaded BLAS. The design and evaluation of a parallel formulation is future work.

• 267.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
A Multimodal Approach to Autonomous Document Categorization Using Convolutional Neural Networks2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

When international students apply for the Swedish educational system, they send documents to verify their merits. These documents are categorized and evaluated by administrators. This thesis approach the problem of document classification with a multimodal convolutional network. By looking at both image and text features together, it is examined if the classification is better than any of the sources alone. The best result for single source classification was when the input was text at 85.2% accuracy, this was topped by the multimodal approach with a accuracy of 88.4%.This thesis concludes that there is a gain in accuracy when using a multimodal approach.

• 268.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
How to provide a user friendly search interface based upon a libraries Open Public Access Catalogue2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Today many libraries offer their services via Internet and reach billions of visitors in different ages. The problem is that most of these library web sites are not customized for the users and they don’t deliver a good user experience. In this thesis we have studied both the interface and the users of an Open Public Access Catalog called CS Library. We found out how the users use the current system and how they want to use it. To achieve this we gathered data with different user studies at the Ume°a city library. A new interface was developed from the outcome of our user study. We created a set of guidelines that were followed when a new user customized design was developed for CS Library. The new design offers a better user experience and is customized by the users needs, desires and thoughts. The new design has been implemented as an interactive prototype with HTML, CSS, Javascript and Actionscript to convey a better feeling of the interface.

• 269. Byers, R.
Umeå University, Faculty of Science and Technology, Departement of Computing Science.
Structured condition numbers for invariant subspaces2006In: Siam Journal on Matrix Analysis and Applications, Vol. 28, no 2, p. 326-347Article in journal (Refereed)

Invariant subspaces of structured matrices are sometimes better conditioned with respect to structured perturbations than with respect to general perturbations. Sometimes they are not. This paper proposes an appropriate condition number c(S), for invariant subspaces subject to structured perturbations. Several examples compare c(S) with the unstructured condition number. The examples include block cyclic, Hamiltonian, and orthogonal matrices. This approach extends naturally to structured generalized eigenvalue problems such as palindromic matrix pencils.

• 270.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Hybrid Clouds: Implementation and obstacles2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

Hybrid cloud is the approach companies want to adopt for its future in the cloud since hybrid cloud allows you to boost the capacity or the capability of a cloud service by aggregation, integration or customization with another cloud service. Those services can be both private or public. Implementing a hybrid cloud is a big process and companies have difficulties finding a good standard for it. In this thesis, the key points and obstacles in the implementation of the hybrid cloud are pinpointed. One obstacle, workflows are studied closer. Workflows are the result of cloud orchestration, arrangement and coordination of automated tasks. The thesis covers the implementation process of workflows. The result of the thesis is key findings and motivation for the implementation of hybrid cloud and how workflows should be implemented

• 271.
Dublin City University, Ireland.
Dublin City University, Ireland. Centre for Research and Technology Hellas, Greece. Centre for Research and Technology Hellas, Greece. Dublin City University, Ireland. Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, High Performance Computing Center North (HPC2N). Dublin City University, Ireland. Dublin City University, Ireland.
A review of cloud computing simulation platforms and related environments2017In: Proceedings of the 7th International Conference on Cloud Computing and Services Science: Volume 1: CLOSER, 2017, Vol. 1, p. 679-691Conference paper (Refereed)

Recent years have seen an increasing trend towards the development of Discrete Event Simulation (DES) platforms to support cloud computing related decision making and research. The complexity of cloud environments is increasing with scale and heterogeneity posing a challenge for the efficient management of cloud applications and data centre resources. The increasing ubiquity of social media, mobile and cloud computing combined with the Internet of Things and emerging paradigms such as Edge and Fog Computing is exacerbating this complexity. Given the scale, complexity and commercial sensitivity of hyperscale computing environments, the opportunity for experimentation is limited and requires substantial investment of resources both in terms of time and effort. DES provides a low risk technique for providing decision support for complex hyperscale computing scenarios. In recent years, there has been a significant increase in the development and extension of tools to support DES for cloud computing resulting in a wide range of tools which vary in terms of their utility and features. Through a review and analysis of available literature, this paper provides an overview and multi-level feature analysis of 33 DES tools for cloud computing environments. This review updates and extends existing reviews to include not only autonomous simulation platforms, but also on plugins and extensions for specific cloud computing use cases. This review identifies the emergence of CloudSim as a de facto base platform for simulation research and shows a lack of tool support for distributed execution (parallel execution on distributed memory systems).

• 272.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
EVALUATION OF MACHINE LEARNING ALGORITHMS FOR SMS SPAM FILTERING2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

The purpose of this thesis is to evaluate different machine learning algorithms and methods for text representation in order to determine what is best suited to use to distinguish between spam SMS and legitimate SMS. A data set that contains 5573 real SMS has been used to train the algorithms K-Nearest Neighbor, Support Vector Machine, Naive Bayes and Logistic Regression. The different methods that have been used to represent text are Bag of Words, Bigram and Word2Vec. In particular, it has been investigated if semantic text representations can improve the performance of classification. A total of 12 combinations have been evaluated with help of the metrics accuracy and F1-score.The results shows that Logistic Regression together with Bag of Words reach the highest accuracy and F1-score. Bigram as text representation seems to work worse then the others methods. Word2Vec can increase the performnce for K-Nearst Neigbor but not for the other algorithms.

• 273.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Collision Detection of TriangleMeshes using GPU2011Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis

Collision detection in physics engines often use primitives such as spheres and boxes since collisions between these objects are straightforward to compute. More complicated objects can then be modeled using compounds of these simpler primitives. However, in the pursuit of making it easier to construct and simulate complicated objects, triangle meshes are a good alternative since it is usually the format used by modeling tools. This thesis demonstrates how triangle meshes can be used directly as collision objects within a physics engine. The collision detection is done using triangle mesh models with tests accelerated using a tree-based bounding volume hierarchy structure. OpenCL is a new open industry framework for writing programs on heterogeneous platforms, including highly parallel platforms such as Graphics Processing Units(GPUs). Through the use of OpenCL, parallelization of triangle mesh collision detection is implemented for the GPU, then evaluated and compared to the CPU implementation

• 274.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Navigating to real life objects in indoor environments using an Augmented Reality headset2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Augmented Reality (AR) headmounts are an rising technology with great chances to be a common gadget used by a lot of people in the near future. With the rise of this technology, new possibilities opens up on how to combine the interaction of the real world together with the virtual world. This thesis meets some of these upcoming interaction questions in terms of indoor navigation. The thesis introduces an approach for designing and implementing an AR-based system that is able to let users navigate around an indoor environment to find various real life objects while using an Augmented Reality headmount. The thesis also discusses how to personalize the navigation to different users in different environments. A proof-of concept was implemented and evaluated with several users inside different indoor environments, e.g., a real food store, where the results showed that users were more effective finding objects while using the AR-based system, compared to when not using the AR-basedsystem.

• 275.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Adaptive least squares matching as a non-linear least squares optimization problem2002In: Proceedings SSAB 2002: symposium on Image Analysis, 2002Conference paper (Other academic)

Adaptive Least Squares Matching (ALSM) is a powerful technique for precisely locating objects in digital images. The method was introduced to the photogrammetric community by Gruen in 1985 and has since been developed further. The purpose of this paper is to study the basic ALSM formulation from a least squares optimization point of view. It turns out that it is possible to describe the basic algorithm as a variation of the Gauss-Newton method for solving weighted non-linear least squares optimization problems. This opens the possibility of applying optimization theory on the ALSM problem. The line-search algorithm for obtaining global convergence is especially described and illustrated

• 276.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Comparison of resection: intersection algorithms and projection geometries in radiostereometry2002In: ISPRS journal of photogrammetry and remote sensing (Print), ISSN 0924-2716, E-ISSN 1872-8235, Vol. 56, no 5-6, p. 390-400Article in journal (Refereed)

Three resection-intersection algorithms were applied to simulated projections and clinical data from radiostereometric patients. On simulated data, the more advanced bundle-adjustment-based algorithms outperformed the classical Selvik algorithm, even if the error reductions were small for some parameters. On clinical data, the results were inconclusive. The two different projection geometries had a much larger influence on the error size and distribution. For the biplanar configuration, the position and motion errors were small and almost isotropic. For the uniplanar configuration, the position errors were comparably high and anisotropic, but still resulted in a high accuracy for some motion parameters at the expense of others. The simplified resection-intersection algorithm by Selvik may still be considered a good and robust algorithm for radiostereometry. More studies will have to be performed to find out how the theoretical advantages of the bundle methods can be utilized in clinical radiostereometry. (C) 2002 Elsevier Science B.V. All rights reserved.

• 277.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Improving the robustness of least squares template matching with a line-search algorithm2002In: Close-range imaging, long-range vision: proceedings of the Commission V symposium, ISPRS , 2002, Vol. 34, no 5, p. 7-11Conference paper (Other academic)

The Adaptive Least Squares Matching (ALSM) problem of Gruen is conventionally described as a statistical estimation problem. This paper shows that the ALSM problem may also be interpreted as a weighted non-linear least squares problem. This enables optimization theory to be applied to the ALSM problem. The ALSM algorithm may be interpreted as an instance of the well-known Gauss-Newton algorithm. A problem-independent termination criteria is introduces based on angles in high-dimensional vector spaces. The line-search modification of the Gauss-Newton method is explained and applied to the ALSM problem. The implications of the line-search modification is an increased robustness, reduced oscillations, and increased pull-in range. A potential drawback is the increased number of convergences toward side minima in images with repeating patterns.

• 278.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Metod och anordning för identifikation och orientering av stereoröntgenbilder2002Patent (Other (popular science, discussion, etc.))
• 279.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
UmRSA Digital Measure — A Measurement Program for Digital Radiostereometry1998In: Proceedings of the SSAB Symposium on Image Analysis, SSAB , 1998, p. 69-71Conference paper (Other academic)
• 280.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
INSA Strasbourg, France.
Bundle adjustment with and without damping2013In: Photogrammetric Record, ISSN 0031-868X, E-ISSN 1477-9730, Vol. 28, no 144, p. 396-415Article in journal (Refereed)

The least squares adjustment (LSA) method is studied as an optimisation problem and shown to be equivalent to the undamped Gauss-Newton (GN) optimisation method. Three problem-independent damping modifications of the GN method are presented: the line-search method of Armijo (GNA); the Levenberg-Marquardt algorithm (LM); and Levenberg-Marquardt-Powell (LMP). Furthermore, an additional problem-specific "veto" damping technique, based on the chirality condition, is suggested. In a perturbation study on a terrestrial bundle adjustment problem the GNA and LMP methods with veto damping can increase the size of the pull-in region compared to the undamped method; the LM method showed less improvement. The results suggest that damped methods can, in many cases, provide a solution where undamped methods fail and should be available in any LSA software package. Matlab code for the algorithms discussed is available from the authors.

• 281.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
INSA Strasbourg, France.
Camera Calibration using the Damped Bundle Adjustment Toolbox2014In: ISPRS Annals - Volume II-5, 2014: ISPRS Technical Commission V Symposium 23–25 June 2014, Riva del Garda, Italy / [ed] F. Remondino and F. Menna, Copernicus GmbH , 2014, Vol. II-5, p. 89-96Conference paper (Refereed)

Camera calibration is one of the fundamental photogrammetric tasks. The standard procedure is to apply an iterative adjustment to measurements of known control points. The iterative adjustment needs initial values of internal and external parameters. In this paper we investigate a procedure where only one parameter - the focal length is given a specific initial value. The procedure is validated using the freely available Damped Bundle Adjustment Toolbox on five calibration data sets using varying narrow- and wide-angle lenses. The results show that the Gauss-Newton-Armijo and Levenberg-Marquardt-Powell bundle adjustment methods implemented in the toolbox converge even if the initial values of the focal length are between 1/2 and 32 times the true focal length, even if the parameters are highly correlated. Standard statistical analysis methods in the toolbox enable manual selection of the lens distortion parameters to estimate, something not available in other camera calibration toolboxes. A standardised camera calibration procedure that does not require any information about the camera sensor or focal length is suggested based on the convergence results. The toolbox source and data sets used in this paper are available from the authors.

• 282.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
INSA Strasbourg, France.
Experiments with Metadata-derived Initial Values and Linesearch Bundle Adjustment in Architectural Photogrammetry2013Conference paper (Refereed)

According to the Waldhäusl and Ogleby (1994) "3x3 rules", a well-designed close-range architetural photogrammetric project should include a sketch of the project site with the approximate position and viewing direction of each image. This orientation metadata is important to determine which part of the object each image covers. In principle, the metadata could be used as initial values for the camera external orientation (EO) parameters. However, this has rarely been used, partly due to convergence problem for the bundle adjustment procedure.

In this paper we present a photogrammetric reconstruction pipeline based on classical methods and investigate if and how the linesearch bundle algorithms of Börlin et al. (2004) and/or metadata can be used to aid the reconstruction process in architectural photogrammetry when the classical methods fail. The primary initial values for the bundle are calculated by the five-point algorithm by Nistér (Stewénius et al., 2006). Should the bundle fail, initial values derived from metadata are calculated and used for a second bundle attempt.

The pipeline was evaluated on an image set of the INSA building in Strasbourg. The data set includes mixed convex and non-convex subnetworks and a combination of manual and automatic measurements.

The results show that, in general, the classical bundle algorithm with five-point initial values worked well. However, in cases where it did fail, linesearch bundle and/or metadata initial values did help. The presented approach is interesting for solving EO problems when the automatic orientation processes fail as well as to simplify keeping a link between the metadata containing the plan of how the project should have become and the actual reconstructed network as it turned out to be.

• 283.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
INSA Strasbourg, France.
External Verification of the Bundle Adjustment in Photogrammetric Software Using the Damped Bundle Adjustment Toolbox2016In: XXIII ISPRS Congress, Commission V: Volume XLI-B5 / [ed] L. Halounova, V. Šafář, F. Remondino, J. Hodač, K. Pavelka, M. Shortis, F. Rinaudo, M. Scaioni, J. Boehm, and D. Rieke-Zapp, International Society of Photogrammetry and Remote Sensing , 2016, Vol. XLI-B5, p. 7-14Conference paper (Refereed)

The aim of this paper is to investigate whether the Matlab-based Damped Bundle Adjustment Toolbox (DBAT) can be used to provide independent verification of the BA computation of two popular software—PhotoModeler (PM) and PhotoScan (PS).

For frame camera data sets with lens distortion, DBAT is able to reprocess and replicate subsets of PM results with high accuracy. For lens-distortion-free data sets, DBAT can furthermore provide comparative results between PM and PS. Data sets for the discussed projects are available from the authors.

The use of an external verification tool such as DBAT will enable users to get an independent verification of the computations of their software. In addition, DBAT can provide computation of quality parameters such as estimated standard deviations, correlation between parameters, etc., something that should be part of best practice for any photogrammetric software. Finally, as the code is free and open-source, users can add computations of their own.

• 284.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
National Institute of Applied Sciences of Strasbourg. Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science.
Pros and cons of constrained and unconstrained formulation of the bundle adjustment problem2004In: ISPRS Congress Istanbul 2004, Proceedings of Commission III, ISPRS , 2004, Vol. XXXV, no B3, p. 589-594Conference paper (Other academic)

Two implementations of the bundle adjustment problem were applied to a subset of the Zurich City Hall reference data set. One implementation used the standard Euler angle parameterisation of the rotation matrix. The second implementation used all nine elements of the rotation matrix as unknowns and six functional constraints. The second formulation was constructed to reduce the non-linearity of the optimisation problem. The hypothesis was that a lower degree of non-linearity would lead to faster convergence. Furthermore, each implementation could optionally use the line search damping technique known from optimisation theory. The algorithms were used to solve the relative orientation problem for a varying number of homologous points from 33 different camera pairs. The results show that the constrained formulation has marginally better convergence properties, with or without damping. However, damping alone halves the number of convergence failures at a minor computational cost. The conclusion is that except to avoid the singularities associated with the Euler angles, the preferred use of the constrained formulation remains an open question. However, the results strongly suggest that the line search damping technique should be included in standard implementations of the bundle adjustment algorithm.

• 285.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
3D measurements of buildings and environment for harbor simulators2009Report (Other academic)

Oryx Simulations develops and manufactures real-time physics simulators for training of harbor crane operator in several of the world’s major harbors. Currently, the modelling process is labor-intensive and a faster solution that can produce accurate, textured models of harbor scenes is desired. The accuracy requirements vary across the scene, and in some areas accuracy can be traded for speed. Due to the heavy equipment involved, reliable error estimates are important throughout the scene. This report surveys the scientific literature of 3D reconstruction algorithms from aerial and terrestrial imagery and laser scanner data. Furthermore, available software solutions are evaluated. The conclusion is that the most useful data source is terrestrial images, optionally complemented by terrestrial laser scanning. Although robust, automatic algorithms exist for several low-level subproblems, no automatic high-level 3D modelling algorithm exists that satisfy all the requirements. Instead, the most successful high-level methods are semi-automatic, and their respective success depend on how well user input is incorporated into an efficient workflow. Furthermore, the conclusion is that existing software cannot handle the full suite of varying requirements within the harbor reconstruction problem. Instead we suggest that a 3D reconstruction toolbox is implemented in a high-level language, Matlab. The toolbox should contain state-of-the-art low-level algorithms that can be used as “building blocks” in automatic or semi-automatic higher-level algorithms. All critical algorithms must produce reliable error estimates. The toolbox approach in Matlab will be able to simultaneously support basic research of core algorithms, evaluation of problem-specific high-level algorithms, and production of industry-grade solutions that can be ported to other programming languages and environments.

• 286.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
University of Western Australia. Massachusetts General Hospital, Boston, MA.
Validation of marker-based X-ray measurements of joint kinematics2006In: Proceedings SSBA 2006: symposium on image analysis / [ed] Fredrik Georgsson, Niclas Börlin, Umeå: Umeå University, Department of Computing Science, Umeå University , 2006, p. 113-116Conference paper (Other academic)

Radiostereometric Analysis (RSA) is an established method for measuring the motion of the skeleton. However, in order to measure dynamic joint kinematics, RSA requires expensive, custom-built hardware. Furthermore, the working volume is restricted to the region around where the beams intersect.

The Single-plane RSA Flouroscopy (SPRSAF) has the potential to overcome these limitations. This paper is the first validation of SPRSAF versus RSA on images with clinical image quality.

The results say that SPRSAF has a rotational error of (1.3,2.9, 11.6) degrees for rotation about the three primary axes. The corresponding translation results are (8.5, 1.0, 1.5) mm. This indicates that SPRSAF has the precision needed to be clinically useful in at least four of the six degrees of freedom.

• 287.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Sahlgrenska University Hospital.
Radiostereometry Based On Digitized Radiographs1997In: Proceedings of the 43rd Annual Meeting of The Orthopaedic Research Society, 1997, p. 626-626Conference paper (Other academic)
• 288.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Medicine, Department of Odontology, Prosthetic Dentistry.
An Implant-oriented method for dental digital subtraction radiography1999In: Computer Methods in Biomechanics & Biomedical Engineering — 2 / [ed] Middleton, J., Gordon and Breach Science Publishers , 1999, p. 705-712Conference paper (Other academic)
• 289.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Medicine, Department of Odontology, Prosthetic Dentistry.
﻿The threaded dental implant as a reference object for image alignment2001In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 4, no 5, p. 421-431Article in journal (Refereed)

This paper presents a method that uses the threaded dental implant as a reference object for the inter-image alignment necessary for digital subtraction radiography. The implant is furthermore used to define a measurement coordinate system and to automate the placement of reference areas used for contrast correction. The method is intended for studies of diffuse bone density changes in the vicinity of the implant. The method is shown to be insensitive to large variations in exposure time and geometry, and is together with the contrast correction method of Ruttimann et al., able to detect clinically invisible simulated bone density changes.

• 290.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science.
A globally convergent gauss-newton algorithm for the bundle adjustment problem with functional constraints2003In: Optical 3-D measurement techniques: applications in GIS, mapping, manifactoring, quality control, robotics, navigation, mobile mapping, medical imaging, VR generation and animation / [ed] A. Gruen, H. Kahmen, Wichmann-Verlag , 2003, Vol. 2, p. 269-276Chapter in book (Other academic)

This paper describes a Gauss-Newton-based algorithm for the bundle adjustment problem with functional constraints (GNC). The GNC algorithm has superior theoretical convergence properties compared to the conventional bundle algorithm. Both algorithms were applied to simulated measurements of a sphere with 2-3 cameras and 4-9 points. For 2 cameras and 4-5 points, the GNC converged in substantially more cases. For the other configurations, the convergence properties were similar. The added cost for the GNC algorithm was less than 0.01 iterations on average. The GNC algorithm need to be evaluated on real-world problems, but the results suggest that the algorithm will be more reliable for minimum data problems and have a minimal overhead for easy problems.

• 291.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
INSA Strasbourg, France. INSA Strasbourg, France.
Implementing Functional Modularity for Processing of General Photogrammetric Data with the Damped Bundle Adjustment Toolbox (DBAT)2019In: Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci., XLII-2/W17, 69–75, 2019 / [ed] P. Grussenmeyer, A. Murtiyoso, H. Macher, and R. Assi, 2019, Vol. XLII-2/W17, p. 69-75Conference paper (Refereed)

The Damped Bundle Adjustment Toolbox (DBAT) is a free, open-source, toolbox for bundle adjustment. The purpose of DBAT is to provide an independent, open-source toolkit for statistically rigorous bundle adjustment computations. The capabilities include bundle adjustment, network analysis, point filtering, forward intersection, spatial intersection, plotting functions, and computations of quality indicators such as posterior covariance estimates and parameter correlations. DBAT is written in the high-level Matlab language and includes several processing example files. The input formats have so far been restricted to PhotoModeler export files and Photoscan (Metashape) native files. Fine-tuning of the processing has so far required knowledge of the Matlab language.

This paper describes the development of a scripting language based on the XML (eXtensible Markup Language) language that allow the user a fine-grained control over what operations are applied to the input data, while keeping the needed programming skills at a minimum. Furthermore, the scripting language allows a wide range of input formats. Additionally, the XML format allows simple extension of the script file format both in terms of adding new operations, file formats, or adding parameters to existing operations. Overall, the script files will in principle allow DBAT to process any kind of photogrammetric input and should extend the usability of DBAT as a scientific and teaching tool for photogrammetric computations.

• 292.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Photogrammetry and Geomatics Group, ICube Laboratory UMR 7357, INSA Strasbourg, France. Photogrammetry and Geomatics Group, ICube Laboratory UMR 7357, INSA Strasbourg, France. 3D Optical Metrology (3DOM) unit, Bruno Kessler Foundation (FBK), Trento, Italy; COMEX SA–Innovation Department, COMEX, Marseille, France. LIS, I&M Team, Aix-Marseille Université, Polytech Luminy, Marseille, France; Institute of Theoretical Physics, ETH Zurich, Zurich, Switzerland.
Flexible Photogrammetric Computations Using Modular Bundle Adjustment: The Chain Rule and the Collinearity Equations2019In: Photogrammetric Engineering and Remote Sensing, ISSN 0099-1112, Vol. 85, no 5, p. 361-368Article in journal (Refereed)

The main purpose of this article is to show that photogrammetric bundle-adjustment computations can be sequentially organized into modules. Furthermore, the chain rule can be used to simplify the computation of the analytical Jacobians needed for the adjustment. Novel projection models can be flexibly evaluated by inserting, modifying, or swapping the order of selected modules. As a proof of concept, two variants of the pinhole projection model with Brown lens distortion were implemented in the open-source Damped Bundle Adjustment Toolbox and applied to simulated and calibration data for a nonconventional lens system. The results show a significant difference for the simulated, error-free, data but not for the real calibration data. The current flexible implementation incurs a performance loss. However, in cases where flexibility is more important, the modular formulation should be a useful tool to investigate novel sensors, data-processing techniques, and refractive models.

• 293.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
INSA Strasbourg, France. INSA Strasbourg, France. 3D Optical Metrology (3DOM) unit, Bruno Kessler Foundation (FBK), Trento, Italy. 3D Optical Metrology (3DOM) unit, Bruno Kessler Foundation (FBK), Trento, Italy.
Modular Bundle Adjustment for Photogrammeric Computations2018In: ISPRS Technical Commission II Symposium 2018, ISPRS , 2018, Vol. XLII-2, p. 133-140Conference paper (Refereed)

In this paper we investigate how the residuals in bundle adjustmentcan be split into a composition of simple functions. According to thechain rule, the Jacobian (linearisation) of the residual can be formedas a product of the Jacobians of the individual steps. Whenimplemented, this enables a modularisation of the computation of thebundle adjustment residuals and Jacobians where each component haslimited responsibility. This enables simple replacement of componentsto e.g. implement different projection or rotation models byexchanging a module. The technique has previously been used toimplement bundle adjustment in the open-source package DBAT (Borlinand Grussenmeyer, ¨ 2013) based on the Photogrammetric and ComputerVision interpretations of Brown (1971) lens distortion model. In thispaper, we applied the technique to investigate how affine distortionscan be used to model the projection of a tilt-shift lens. Two extendeddistortion models were implemented to test the hypothesis that theordering of the affine and lens distortion steps can be changed toreduce the size of the residuals of a tilt-shift lens calibration.Results on synthetic data confirm that the ordering of the affine andlens distortion steps matter and is detectable by DBAT. However, whenapplied to a real camera calibration data set of a tilt-shift lens, nodifference between the extended models was seen. This suggests thatthe tested hypothesis is false and that other effects need to bemodelled to better explain the projection. The relatively lowimplementation effort that was needed to generate the models suggestthat the technique can be used to investigate other novel projectionmodels in photogrammetry, including modelling changes in the 3Dgeometry to better understand the tilt-shift lens.

• 294.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Katholieke Universiteit Nijmegen, Nijmegen, Holland. Sahlgrenska University Hospital, Göteborg, Sweden.
The precision of radiostereometric measurements: manual vs. digital measurements2002In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 35, no 1, p. 69-79Article in journal (Refereed)

The precision of digital vs. manual radiostereometric measurements in total hip arthroplasty was evaluated using repeated stereoradiographic exposures with an interval of 10–15 min. Ten Lubinus SP2 stems cemented into bone specimens and 12 patients with the same stem design were used to evaluate the precision of stem translations and rotations. The precision of translations and rotations of the cup and femoral head penetration was studied in 12 patients with whole polyethylene cups.

The use of a measurement method based on digitised radiographs improved the precision for some of the motion parameters, whereas many of them did not change. A corresponding pattern was observed for both the intra- and interobserver error. Of the wear parameters, the most pronounced improvements were the 3D wear and in the proximal-distal direction, although the anterior-posterior precision was also improved. The mean errors of rigid body and elliptic fitting decreased in all evaluations but one, consistent with a more reproducible identification of the markers centres and the edge of the femoral head.

Increased precision of radiostereometric measurements may be used to increase the statistical power of future randomised studies and to study new fields in orthopaedics requiring higher precision than has been available with RSA based on manual measurements.

• 295. Börstler, Jurgen
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Beauty and the Beast: on the readability of object-oriented example programs2016In: Software quality journal, ISSN 0963-9314, E-ISSN 1573-1367, Vol. 24, no 2, p. 231-246Article in journal (Refereed)

Some solutions to a programming problem are more elegant or more simple than others and thus more understandable for students. We review desirable properties of example programs from a cognitive and a measurement point of view. Certain cognitive aspects of example programs are captured by common software measures, but they are not sufficient to capture a key aspect of understandability: readability. We propose and discuss a simple readability measure for software, SRES, and apply it to object-oriented textbook examples. Our results show that readability measures correlate well with human perceptions of quality. Compared with other readability measures, SRES is less sensitive to commenting and whitespace. These results also have implications for software maintainability measures.

• 296.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science. Umeå University, Faculty of Science and Technology, Department of Computing Science.
Evaluating OO Example Programs for CS12008In: Proceedings of the 13th annual conference on Innovation and technology in computer science education, 2008, p. 47-52Conference paper (Refereed)
• 297.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science. Glasgow Caledonian University, Scotland, UK.
On the quality of examples in introductory Java textbooksIn: Transactions on Computing EducationArticle in journal (Refereed)

Example programs play an important role in the teaching and learning of programming. Students as well as teachers rank examples as the most important resources for learning to program. Ex- ample programs work as role models and must therefore always be consistent with the principles and rules we are teaching.

However, it is difficult to find or develop examples that are fully faithful to all principles and guidelines of the object-oriented paradigm and also follow general pedagogical principles and practices. Unless students are able to engage with good examples, they will not be able to tell desirable from undesirable properties in their own and others’ programs.

In this paper we report on a study in which experienced educators evaluated the quality of object-oriented example programs for novices from popular Java textbooks. The evaluation was accomplished using an on-line checklist that elicited responses on the technical, object-oriented, and didactic quality of examples.

In total 25 reviewers contributed 215 reviews to our data set, based on 38 example programs from 13 common introductory programming textbooks. Results show that the evaluation instru- ment is reliable in terms of inter-rater agreement. Overall, example quality was not as good as one might expect from common textbooks, in particular regarding certain object-oriented properties.

We conclude that educators should be careful when taking examples straight out of a textbook.

• 298.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Classes or Objects? CRC-cards Considered Harmful: Extended Abstract2004In: First Workshop of the Scandinavian Pedagogy of Programming Network, 2004Conference paper (Refereed)
• 299.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
CRC-Cards and Roleplay Diagrams--Informal Tools to Teach OO Thinking2007In: 2nd Workshop on Computer Science Education, 2007Conference paper (Refereed)
• 300.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Improving CRC-Card Role-Play with Role-Play Diagrams2005In: OOPSLA'05 Addendum to the Proceedings (Educators' Syposium), 2005, p. 356-364Conference paper (Refereed)
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