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  • 1.
    Berglund, Tomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Brodnik, Andrej
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Mrozek, Kent
    Staffansson, Mats
    Luleå tekniska universitet.
    Söderkvist, Inge
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Minimum curvature variation B-splines: validation of a path-planning model2004Report (Other academic)
  • 2.
    Berglund, Tomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Brodnik, Andrej
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Staffansson, Mats
    Luleå tekniska universitet.
    Söderkvist, Inge
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Planning smooth and obstacle-avoiding b-spline paths for autonomous mining vehicles2010In: IEEE Transactions on Automation Science and Engineering, ISSN 1545-5955, E-ISSN 1558-3783, Vol. 7, no 1, 167-172 p.Article in journal (Refereed)
    Abstract [en]

    We study the problem of automatic generation of smooth and obstacle-avoiding planar paths for efficient guidance of autonomous mining vehicles. Fast traversal of a path is of special interest. We consider four-wheel four-gear articulated vehicles and assume that we have an a priori knowledge of the mine wall environment in the form of polygonal chains. Computing quartic uniform B-spline curves, minimizing curvature variation, staying at least at a proposed safety margin distance from the mine walls, we plan high speed paths.

  • 3.
    Berglund, Tomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Erikson, Ulf
    Luleå tekniska universitet.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Mrozek, Kent
    Navigator AB.
    Söderkvist, Inge
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Automatic generation of smooth paths bounded by polygonal chains2001In: CIMCA 2001: 2001 international conference on computational intelligence for modelling, control & automation : 9-11 July 2001, Las Vegas, Nevada, USA : proceedings / [ed] M. Mohammadian, CIMCA , 2001, 528-535 p.Conference paper (Refereed)
  • 4. Berglund, Tomas
    et al.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Söderkvist, Inge
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    An obstacle-avoiding minimum variation B-spline problem2003In: Proceedings: 2003 International Conference on Geometric Modeling and Graphics, GMAG 2003 ; 16 - 18 July 2003, London, England, Los Alamitos, Calif: IEEE Communications Society, 2003, 156-161 p.Conference paper (Refereed)
    Abstract [en]

    We study the problem of computing a planar curve, restricted to lie between two given polygonal chains, such that the integral of the square of arc-length derivative of curvature along the curve is minimized. We introduce the minimum variation B-spline problem, which is a linearly constrained optimization problem over curves, defined by B-spline functions only. An empirical investigation indicates that this problem has one unique solution among all uniform quartic B-spline functions. Furthermore, we prove that, for any B-spline function, the convexity properties of the problem are preserved subject to a scaling and translation of the knot sequence defining the B-spline.

  • 5.
    Berglund, Tomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Söderkvist, Inge
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    The problem of computing an obstacle-avoiding minimum variation B-spline2003Report (Other academic)
    Abstract [en]

    We study the problem of computing a planar curve restricted to lie between two given polygonal chains such that the integral of the square of arc- length derivative of curvature along the curve is minimized. We introduce the Minimum Variation B-spline problem which is a linearly constrained optimization problem over curves defined by B-spline functions only. An empirical investigation indicates that this problem has one unique solution among all uniform quartic B-spline functions. Furthermore, we prove that, for any B-spline function, the convexity properties of the problem are preserved subject to a scaling and translation of the knot sequence defining the B-spline.

  • 6.
    Berglund, Tomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Strömberg, Thomas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Söderkvist, Inge
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Epi-convergence of minimum curvature variation B-splines2003Report (Other academic)
    Abstract [en]

    We study the curvature variation functional, i.e., the integral over the square of arc-length derivative of curvature, along a planar curve. With no other constraints than prescribed position, slope angle, and curvature at the endpoints of the curve, the minimizer of this functional is known as a cubic spiral. It remains a challenge to effectively compute minimizers or approximations to minimizers of this functional subject to additional constraints such as, for example, for the curve to avoid obstacles such as other curves. In this paper, we consider the set of smooth curves that can be written as graphs of three times continuously differentiable functions on an interval, and, in particular, we consider approximations using quartic uniform B- spline functions. We show that if quartic uniform B-spline minimizers of the curvature variation functional converge to a curve, as the number of B-spline basis functions tends to infinity, then this curve is in fact a minimizer of the curvature variation functional. In order to illustrate this result, we present an example of sequences of B-spline minimizers that converge to a cubic spiral.

  • 7. Brodnik, Andrej
    et al.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Rossi, P.G.
    Tasso, Carlo
    Interoperability and semantic filtering2006In: Je-LKS: Journal of e-Learning and Knowledge Society, ISSN 1826-6223, E-ISSN 1971-8829, Vol. 2, no 2, 165-175 p.Article in journal (Refereed)
    Abstract [en]

    Interoperability is often seen only as a technological problem related to reusability. We would like to give interoperability a new role in the structure of the learning environment and in collaborative activities. For us interoperability is also connected with didactical, semiotic and cultural aspects. It improves the interaction between the materials produced with different tools, the construction of kaleidoscopic artifacts and the refl ection on the learning process.

  • 8.
    Carlsson, Svante
    et al.
    Luleå tekniska universitet.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    A linear-time approximation to the Zookeeper's Problem2000Report (Other academic)
    Abstract [en]

    An algorithm that computes the exact solution to the general Zookeeper's Problem in O(n^2) time has been published. There is also an algorithm that solves the restricted Zookeeper's Problem in O(n\log n) time. In this paper, we give a simple O(n) time algorithm for computing an approximate solution to both the general and the restricted Zookeeper's Problem. Such an approximation route is at most a factor 6 times longer than the shortest route in the exact solution.

  • 9.
    Carlsson, Svante
    et al.
    Luleå tekniska universitet.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Computing a shortest watchman path in a simple polygon in polynomial-time1995In: Algorithms and Data Structures 4th International Workshop, WADS '95, Proceedings / [ed] Selim G. Akl, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 1995, 122-134 p.Conference paper (Refereed)
    Abstract [en]

    In this paper we present the first polynomial-time algorithm for finding the shortest polygonal chain in a simple polygon such that each point of the polygon is visible from some point on the chain. This chain is called the shortest watchman path, or equivalently, the shortest weakly visible curve of the polygon. In proving this result we also give polynomial time algorithms for finding the shortest aquarium-keeper's path that visits all edges of the polygon, and for finding the shortest postman path that visits all vertices of a polygon.

  • 10.
    Carlsson, Svante
    et al.
    Luleå tekniska universitet.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Nilsson, Bengt
    Department of Computer Science, Lund University.
    Finding the shortest watchman route in a simple polygon1999In: Discrete & Computational Geometry, ISSN 0179-5376, E-ISSN 1432-0444, Vol. 22, no 3, 377-402 p.Article in journal (Refereed)
    Abstract [en]

    We present the first polynomial time algorithm that finds the shortest route in a simple polygon such that all points of the polygon are visible from the route. This route is called the shortest watchman route, and we do not assume any restrictions on the route or on the simple polygon. Our algorithm runs in worst case O(n6) time, but it is adaptive, making it run faster on polygons with a simple structure

  • 11.
    Carlsson, Svante
    et al.
    Luleå tekniska universitet.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Nilsson, Bengt J.
    Department of Computer Science, Lund University.
    Finding the shortest watchman route in a simple polygon1993In: Algorithms and Computation 4th International Symposium, ISAAC '93: Proceedings / [ed] K.W. Ng, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 1993, 58-67 p.Conference paper (Refereed)
    Abstract [en]

    We present the first polynomial-time algorithm that finds the shortest route in a simple polygon such that all points of the polygon is visible from some point on the route. This route is sometimes called the shortest watchman route, and it does not allow any restrictions on the route or on the simple polygon. Our algorithm runs in O(n 3) time.

  • 12.
    Johnsson, Helena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Alerby, Eva
    Luleå University of Technology, Department of Arts, Communication and Education, Education, Language, and Teaching.
    Hyyppä, Kalevi
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Karlberg, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Stenberg, Magnus
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science.
    Strömberg, Thomas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    En pedagogisk idé för ingenjörsutbildningarna vid Luleå tekniska universitet2009Conference paper (Refereed)
    Abstract [sv]

    Utmärkande för Luleå tekniska universitet (LTU) har länge varit närheten mellan studenterna och lärarna vilket har manifesterats genom klassrumsundervisning, lärartillgänglighet, mindre studiegrupper, koncentrerade campus etc. Undervisningsformerna har dock ändrats till att idag omfatta dels klassiska föreläsningar i stora studentgrupper, men också projektarbete i team där totalt sett 1/3 av all undervisning vid Luleå tekniska universitet sker i projektform. En fråga har ställts: Har Luleå tekniska universitet idag en gemensam pedagogisk idé för ingenjörsutbildningarna? I så fall är ytterligare en fråga hur denna pedagogiska idé tar sig uttryck i organisationen?Intervjuer med 40 aktiva lärare vid Luleå tekniska universitet har genomförts av projektgruppen (tillika författarna) varpå svaren har grupperats och analyserats i fjorton olika teman. Från dessa teman har sedan fyra hörnstenar i en definition av en pedagogisk idé aggregerats. Formuleringen av den pedagogiska idén lyder: Ett aktivt lärande för yrkeslivet – i branschnära projekt och med god vetenskaplig grund tränas förmågan att arbeta som ingenjör genom coachning från lärare i ett nära och öppet klimat. Idén har antagits av den tekniska fakultetsnämnden vid Luleå tekniska universitet och verifierats på institutionerna. Exempel på implementering och hur den pedagogiska idén aktivt verkar presenteras i artikeln.

  • 13.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    A robust and fast algorithm for computing exact and approximate shortest visiting routes2004In: Computational Science and Its Applications - ICCSA 2004 International Conference, Proceedings, Encyclopedia of Global Archaeology/Springer Verlag, 2004, Vol. Part III, 168-177 p.Conference paper (Refereed)
    Abstract [en]

    Given a simple n-sided polygon in the plane with a boundary partitioned into subchains some of which are convex and colored, we consider the following problem: Which is the shortest route (closed path) contained in the polygon that passes through a given point on the boundary and intersects at least one vertex in each of the colored subchains? We present an optimal algorithm that solves this problem in O(n) time. Previously it was known how to solve the problem optimally when each colored subchain contains one vertex only. Moreover, we show that a solution computed by the algorithm is at most a factor times longer than the overall shortest route that intersects the subchains (not just at vertices) if the minimal distance between vertices of different subchains is at least c times the maximal length of an edge of a subchain. Without such a bound its length can be arbitrarily longer. Furthermore, it is known that algorithms for computing such overall shortest routes suffer from numerical problems. Our algorithm is not subject to such problems.

  • 14.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    An approximative solution to the Zookeeper's Problem2003In: Information Processing Letters, ISSN 0020-0190, E-ISSN 1872-6119, Vol. 87, no 6, 301-307 p.Article in journal (Refereed)
    Abstract [en]

    Consider a simple polygon P containing disjoint convex polygons each of which shares an edge with P. The Zookeeper's Problem then asks for the shortest route in P that visits all convex polygons without entering their interiors. Existing algorithms that solve this problem run in time super-linear in the size of P and the convex polygons. They also suffer from numerical problems. In this paper, we shed more light on the problem and present a simple linear time algorithm for computing an approximate solution. The algorithm mainly computes shortest paths and intersections between lines using basic data structures. It does not suffer from numerical problems. We prove that the computed approximation route is at most 6 times longer than the shortest route in the exact solution.

  • 15.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Användning av MOOC-verktyg i en campuskurs om objektorienterad programmering och design2014In: NU 2014: Umeå 8-10 oktober : abstracts, Umeå: Umeå universitet. Pedagogiska institutionen , 2014, 202- p.Conference paper (Refereed)
  • 16.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Guarding art galleries with one guard1995Licentiate thesis, comprehensive summary (Other academic)
  • 17.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Motivating and Preparing First-Year Students in Computer and Engineering Science2013In: 2013 Frontiers in Education Conference (FIE 2013): Oklahoma City, Olöahoma, USA, 23-26 October 2013, Piscataway, NJ: IEEE Communications Society, 2013, 1096-1102 p.Conference paper (Refereed)
    Abstract [en]

    During recent years the interest in Engineering Studies has declined at universities both in the United States and in many Western European countries including Sweden. In addition, among those students that do enroll, an increasing number drop-out. This paper presents an attempt to mitigate these worrying problems in the form of a new kind of intro- ductory course for first-year engineering students studying on a 5-year long Master of Science program in Computer Science and Engineering. The course is novel in that it takes a holistic approach to motivate and prepare students for their further studies. Core subjects and useful tools are mixed together into an intense 10-week course with 12 separate course modules on different topics, often running in parallel. The course has a total of 21 individual examinations to take, tasks to carry out, and deadlines to meet. The examinations and tasks are chosen among those common in our School of Engineering. Evaluations show that, although demanding for the students, the course works well and fulfills its goals.

  • 18.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    The Euclidean traveling salesman problem with neighborhoods and a connecting fence2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    An important class of problems in robotics deals with the planning of paths. In this thesis, we study this class of problems from an algorithmic point of view by considering cases where we have complete knowledge of the environment and each solution must ensure that a point-sized robot capable of moving continuously and turning arbitrarily accomplishes the following: (1) visits a given set of objects attached to an impenetrable simple polygon in the plane, and (2) travels along a path of minimum length over all the possible paths that visit the objects without crossing the polygon. In its general form, this is The (Euclidean) Traveling Salesman Problem with Neighborhoods and a Connecting Fence. We make several contributions. One is an algorithm that computes a shortest watchman path in a rectilinear polygon in time polynomial in the size of the polygon. Each point in the polygon is visible from some point along the computed path, which is a shortest visiting path for a set of convex polygons, each of which is bounded by a chord in the interior of the polygon. For the special case of computing a shortest watchman route, where the end points of the resulting path must coincide, we give a polynomial-time algorithm for general simple polygons. We also give substantially faster and more practical algorithms for computing provably short approximations, that is watchman paths/routes with lengths guaranteed to be at most a constant times longer than the length of a shortest watchman path/route only. To achieve one of these approximations, we develop a linear-time algorithm for computing a constant factor approximation in the case where the convex polygons are impenetrable. For this problem, which is called the Zookeeper's Problem, we show how an exact solution can be computed in linear time when the number of convex polygons is constant. We also present an application of our results to the computation of both exact and approximate solutions to the problem of computing a shortest visiting route for a set of lines in the plane.

  • 19.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    The Traveling Salesman Problem for lines in the plane2002In: Information Processing Letters, ISSN 0020-0190, E-ISSN 1872-6119, Vol. 82, no 3, 137-142 p.Article in journal (Refereed)
    Abstract [en]

    We present an algorithm that computes the shortest route that intersects n lines in the plane in time polynomial in n; the time complexity is dominated by the time it takes to compute a shortest watchman route in a simple polygon of size n. We also present a simple O(n) time algorithm for computing a route that intersects the lines but which is guaranteed to have a length at most √2 times longer than the shortest route.

  • 20.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Using flipped classroom, peer discussion, and just-in-time teaching to increase learning in a programming course2016In: 2015 IEEE Frontiers in Education Conference: FIE 2015, El Paso, TX 21-24 Oct. 2015, Piscataway, NJ: IEEE Communications Society, 2016Conference paper (Refereed)
    Abstract [en]

    In this paper we report on an experiment conducted in an attempt to improve further the learning environment in a basic campus course on Object-Oriented Programming and Design given to first-year engineering students studying Computer Science and Engineering. This course has for years had the same traditional set-up that is common also in other engineering schools around the world including lectures, mandatory programming assignments, and a final written exam. What we did was to substitute the lectures for in-class sessions based on a variant of the teaching method known as 'flipping the classroom' combined with certain elements of Peer Discussion and Just-in-time teaching. To make all this work, we introduced a web-based MOOC tool into the course. To be able to investigate the quantitative effects of our experiment, we had an experiment class consisting of 70 students taking the course in this new way and a control class of 57 students taking the course in the traditional way. On the final written exam, which was identical for the two classes and marked the same way, 81% of the students in the experiment class passed compared to 60% in the control class. Moreover, the share of students passing with good grades was 58% in the experiment class compared to 32% in the control class. So, not only did the share of students passing the course increase by a third, but also the share of students passing with good grades almost doubled

  • 21.
    Jonsson, Håkan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Sundberg, Sofia
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    On the problem of computing zookeeper routes2004Report (Other academic)
    Abstract [en]

    The Zookeeper's Problem is a shortest-path problem that, given a simple polygon (a zoo) containing a set of disjoint convex polygons (cages) attached to the boundary of the zoo, asks for a shortest route (closed path) in the zoo that intersects the boundaries of all cages without entering their interiors. The literature contains several algorithms for variants of this problem some of which compute exact and some approximate solutions. However, no implementations have been reported. Moreover, concerns have also been raised about the numerical properties of the algorithms that compute exact solutions. In this paper we present a study of two algorithms for the Zookeeper's Problem. One of them compute exact solutions and the other provably good approximations. We give observations about the algorithms and the solutions they compute. We also present an experimental study based on an implementation of the algorithms in Java.

  • 22.
    Kikhia, Basel
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Boytsov, Andrey
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Hallberg, Josef
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Sani, Zaheer ul Hussain
    Luleå University of Technology, Department of Health Sciences.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Synnes, Kåre
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Structuring and presenting lifelogs based on location data2012Report (Other academic)
    Abstract [en]

    Lifelogging techniques help individuals to log their life and retrieve important events, memories and experiences. Structuring lifelogs is a major challenge in lifelogging systems since the system should present the logs in a concise and meaningful way to the user. In this article the authors present a novel approach for structuring lifelogs as places and activities based on location data. The structured lifelogs are achieved using a combination of density-based clustering algorithms and convex hull construction to identify the places of interest. The periods of time where the user lingers at the same place are then identified as possible activities. In addition to structuring lifelogs the authors present an application in which images are associated to the structuring results and presented to the user for reviewing. The proposed approach allows automatic inference of information about significant places and activities, which generates structured image-annotated logs of everyday life.

  • 23.
    Kikhia, Basel
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Boytsov, Andrey
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Hallberg, Josef
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Sani, Zaheer ul Hussain
    Luleå University of Technology, Department of Health Sciences.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Synnes, Kåre
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Structuring and Presenting Lifelogs based on Location Data2014In: Pervasive Computing Paradigms for Mental Health: 4th International Symposium, MindCare 2014, Tokyo, Japan, May 8-9, 2014, Revised Selected Papers / [ed] Pietro Cipresso; Alaksandar Matic; Guillaume Lopez, Cham: Encyclopedia of Global Archaeology/Springer Verlag, 2014, 133-144 p.Conference paper (Refereed)
    Abstract [en]

    Lifelogging techniques help individuals to log their life and retrieve important events, memories and experiences. Structuring lifelogs is a major challenge in lifelogging systems since the system should present the logs in a concise and meaningful way to the user. In this paper the authors present an approach for structuring lifelogs as places and activities based on location data. The structured lifelogs are achieved using a combination of density-based clustering algorithms and convex hull construction to identify the places of interest. The periods of time where the user lingers at the same place are then identified as possible activities. In addition to structuring lifelogs the authors present an application in which images are associated to the structuring results and presented to the user for reviewing. The system is evaluated through a user study consisting of 12 users, who used the system for 1 day and then answered a survey. The proposed approach in this paper allows automatic inference of information about significant places and activities, which generates structured image-annotated logs of everyday life.

  • 24.
    Landström, Anders
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Nellros, Frida
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Thurley, Matthew
    Image reconstruction by prioritized incremental normalized convolution2011In: Image analysis: 17th Scandinavian conference, SCIA 2011, Ystad, Sweden, May 2011 ; proceedings / [ed] Anders Heyden; Fredrik Kahl, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 2011, 176-185 p.Conference paper (Refereed)
    Abstract [en]

    A priority-based method for pixel reconstruction and incrementalhole filling in incomplete images and 3D surface data is presented.The method is primarily intended for reconstruction of occluded areasin 3D surfaces and makes use of a novel prioritizing scheme, based on apixelwise defined confidence measure, that determines the order in whichpixels are iteratively reconstructed. The actual reconstruction of individualpixels is performed by interpolation using normalized convolution.The presented approach has been applied to the problem of reconstructing3D surface data of a rock pile as well as randomly sampled imagedata. It is concluded that the method is not optimal in the latter case,but the results show an improvement to ordinary normalized convolutionwhen applied to the rock data and are in this case comparable to thoseobtained from normalized convolution using adaptive neighborhood sizes.

  • 25.
    Landström, Anders
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Simonsson, Arne
    Ericsson Research, Luleå.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Voronoi-based ISD and site density characteristics for mobile networks2012In: 2012 IEEE 76th Vehicular Technology Conference: VTC2012-Fall: Towards Sustainable Mobility; Proceedings, Piscataway, NJ: IEEE Communications Society, 2012Conference paper (Refereed)
    Abstract [en]

    Inter-Site Distance (ISD) is a common measure for characterizing the site density in a mobile network However, obtaining a good estimation of the ISD for a real world network is not trivial since the physical layout is usually quite more complex than a perfect theoretical hexagonal grid, due to a number of unavoidable factors such as site availability and traffic density. Voronoi diagrams have been suggested for approximating cells from network layouts, providing a method for partitioning the covered area into cells defined by the proximity to the given set of sites. This yields a framework for site coverage approximation based on the actual site distribution, rather than an underlying theoretical model.We present a novel measure, based on Voronoi diagrams, for characterizing the site density of a cellular network and provide a comparison to the more traditional ISD measure. This measure improves capacity assessments and modeling of real networks.

  • 26.
    Landström, Anders
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Thurley, Matthew
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Adaptive Morphological Filtering of Incomplete Data2014In: 2013 International Conference on Digital Image Computing: Techniques and Applications (DICTA 2013): Hobart, Australia, 26-28 Nov. 2013, Piscataway, NJ: IEEE Communications Society, 2014, 6691479Conference paper (Refereed)
    Abstract [en]

    We demonstrate how known convolution techniques for uncertain data can be used to set the shapes of structuring elements in adaptive mathematical morphology, enabling robust morphological processing of partially occluded or otherwise incomplete data. Results are presented for filtering of both gray-scale images containing missing data and 3D profile data where information is missing due to occlusion effects. The latter demonstrates the intended use of the method: enhancement of crack signatures in a surface inspection system for casted steel.The presented method is able to disregard unreliable data in a systematic and robust way, enabling adaptive morphological processing of the available information while avoiding any false edges or other unwanted features introduced by the values of faulty pixels.

  • 27.
    Landström, Anders
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Thurley, Matthew
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Sub-millimeter crack detection in casted steel using color photometric stereo2014In: 2013 International Conference on Digital Image Computing Techniques and Applications (DICTA 2013: Hobart, Australia, 26-28 November 2013, Piscataway, NJ: IEEE Communications Society, 2014, 6691532Conference paper (Refereed)
    Abstract [en]

    A novel method for automated inspection of small corner cracks in casted steel is presented, using a photometric stereo setup consisting of two light sources of different colors in conjunction with a line-scan camera. The resulting image is separated into two different reflection patterns which are used to cancel shadow effects and estimate the surface gradient. Statistical methods are used to first segment the image and then provide an estimated crack probability for each segmented region. Results show that true cracks are successfully assigned a high crack probability, while only a minor proportion of other regions cause similar probability values. About 80% of the cracks present in the segmented regions are given a crack probability higher than 70%, while the corresponding number for other non-crack regions is only 5%. The segmented regions contain over 70% of the manually identified crack pixels. We thereby provide proof-of-concept for the presented method.

  • 28.
    Nellros, Frida
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Thurley, Matthew
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Andersson, Charlotte
    LKAB.
    Forsmo, Seija
    LKAB.
    Automated measurement of sintering degree in optical microscopy through image analysis of particle joins2015In: Pattern Recognition, ISSN 0031-3203, E-ISSN 1873-5142, Vol. 48, no 11, 3451-3465 p.Article in journal (Refereed)
    Abstract [en]

    In general terms, sintering describes the bonding of particles into a more coherent structure, where joins form between packed particles, usually as a result of heating. Characterization of sintering is an important topic in the fields of metallurgy, steel, iron ore pellets, ceramics, and snow for understanding material properties and material strength. Characterization using image analysis has been applied in a number of these fields but is either semi-automatic, requiring human interaction in the analysis, or based on statistical sampling and stereology to characterize the sample. This paper presents a novel fully automatic image analysis algorithm to analyze and determine the degree of sintering based on analysis of the particle joins and structure. Quantitative image analysis of the sintering degree is demonstrated for samples of iron ore pellets but could be readily applied to other packed particle materials. Microscope images of polished cross-sections of iron ore pellets have been imaged in their entirety and automated analysis of hundreds of images has been performed. Joins between particles have been identified based on morphological image processing and features have been calculated based on the geometric properties and curvature of these joins. The features have been analyzed and determined to hold discriminative power by displaying properties consistent with sintering theory and results from traditional pellet diameter measurements on the heated samples, and a statistical evaluation using the Welch t-test.

  • 29.
    Thurley, Matthew
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Landström, Anders
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Project: VSB - Vision Systems Business Development Platform2012Other (Other (popular science, discussion, etc.))
  • 30.
    Thurley, Matthew
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Nellros, Frida
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Project: HLRC PIA - Automated Image Analysis for Quantitative Characterisation of Iron Ore Pellet Structures2012Other (Other (popular science, discussion, etc.))
  • 31.
    Wiss, Ulrika
    et al.
    Luleå tekniska universitet.
    Carr, David
    Luleå tekniska universitet.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Evaluating 3-dimensional information visualizaton designs1998Report (Other academic)
    Abstract [en]

    A number of three-dimensional information visualization designs have been invented during the last years. However, comparisons of such designs have been scarce, making it difficult for application developers to select a suitable design. This paper reports on a case study where three existing visualization designs have been implemented and evaluated. We found that the three visualization designs have inherent problems when used for visualizing different data sets, and that certain tasks can not be supported by the designs. We propose a multi-visualization view to overcome these problems. Finally, the paper also introduces heuristics for selecting information visualization designs

  • 32.
    Wiss, Ulrika
    et al.
    Luleå tekniska universitet.
    Carr, David
    Luleå tekniska universitet.
    Jonsson, Håkan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Evaluating three-dimensional information visualization designs: a case study of three designs1998In: Proceedings: 1998 IEEE Conference on Information Visualization, July 29 - 31, 1998, London, England : an international conference on computer visualization & graphics / [ed] Ebad Banissi, Los Alamitos, Calif: IEEE Communications Society, 1998, 137-144 p.Conference paper (Refereed)
    Abstract [en]

    A number of 3D information visualization designs have been invented during the last few years. However, comparisons of such designs have been scarce, making it difficult for application developers to select a suitable design. This paper reports on a case study where three existing visualization designs have been implemented and evaluated. We found that the three information visualization designs have inherent problems when used for visualizing different data sets, and that certain tasks cannot be supported by the designs. A general methodology for evaluation is presented, which comprises the evaluation of suitability for different data sets as well as the evaluation of support for user tasks

1 - 32 of 32
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