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1.
  • Eriksson, Anders P, et al. (författare)
  • On the bijectivity of thin-plate splines
  • 2012
  • Ingår i: Analysis for Science, Engineering and Beyond, The Tribute Workshop in Honour of Gunnar Sparr held in Lund, May 8-9, 2008. - Springer. - 978-3-642-20235-3 (print) - 978-3-642-20236-0 ; 6, s. 93-141
  • Bokkapitel (övrigt vetenskapligt)abstract
    • The thin-plate spline (TPS) has been widely used in a number of areas such as image warping, shape analysis and scattered data interpolation. Introduced by Bookstein (IEEE Trans. Pattern Anal. Mach. Intell. 11(6):567–585 1989), it is a natural interpolating function in two dimensions, parameterized by a finite number of landmarks. However, even though the thin-plate spline has a very intuitive interpretation as well as an elegant mathematical formulation, it has no inherent restriction to prevent folding, i.e. a non-bijective interpolating function. In this chapter we discuss some of the properties of the set of parameterizations that form bijective thin-plate splines, such as convexity and boundness. Methods for finding sufficient as well as necessary conditions for bijectivity are also presented. The methods are used in two settings (a) to register two images using thin-plate spline deformations, while ensuring bijectivity and (b) group-wise registration of a set of images, while enforcing bijectivity constraints.
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2.
  • Johansson, Karl Henrik, et al. (författare)
  • Fast Switches in Relay Feedback Systems
  • 1999
  • Ingår i: Automatica. ; 35:4, s. 539-552
  • Tidskriftsartikel (refereegranskat)abstract
    • Relays are common in automatic control systems. Even linear systems with relay feedback are, however, far from fully understood. New results are given about the behavior of these systems via a state-space approach. It is proved that there exist multiple fast switches if and only if the sign of the first nonvanishing Markov parameter of the linear system is positive. Fast switches are shown to occur as part of stable limit cycles. An analysis is developed for these limit cycles that illustrates how they can be predicted.
3.
  • Karlsson, Johan, et al. (författare)
  • Shape Modeling by Optimising Description Length Using Gradients and Parameterisation Invariance
  • 2012
  • Ingår i: Analysis for Science, Engineering and Beyond, The Tribute Workshop in Honour of Gunnar Sparr held in Lund, May 8-9, 2008. - Springer. - 978-3-642-20236-0 (online) - 978-3-642-20235-3 (print) ; 6, s. 51-91
  • Bokkapitel (övrigt vetenskapligt)abstract
    • In Statistical Shape Modeling, a dense correspondence between the shapes in the training set must be established. Traditionally this has been done by hand, a process that commonly requires a lot of work and is difficult, especially in 3D. In recent years there has been a lot of work on automatic construction of Shape Models. In recent papers (Davies et al., Medical Image Computing and Computer-Assisted Intervention MICCAI’2001, pp. 57–65, 2001; Davies et al., IEEE Trans. Med. Imaging. 21(5):525–537 2002; Kotcheff and Taylor, Med. Image Anal. 2:303–314 1998) Minimum Description Length, (MDL), is used to locate a dense correspondence between shapes. In this paper the gradient of the description length is derived. Using the gradient, MDL is optimised using steepest descent. The optimisation is therefore faster and experiments show that the resulting models are better. To characterise shape properties that are invariant to similarity transformations, it is first necessary to normalise with respect to the similarity transformations. This is normally done using Procrustes analysis. In this paper we propose to align shapes using the MDL criterion. The MDL based algorithm is compared to Procrustes on a number of data sets. It is concluded that there is improvement in generalisation when using MDL to align the shapes. In this paper novel theory to prevent the commonly occurring problem of clustering under correspondence optimisation is also presented. The problem is solved by calculating the covariance matrix of the shapes using a scalar product that is invariant to mutual reparameterisations. An algorithm for implementing the ideas is proposed and compared to Thodberg’s state of the art algorithm for automatic shape modeling. The suggested algorithm is more stable and the resulting models are of higher quality according to the generalisation measure and according to visual inspection of the specificity.
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5.
  • Anton, J. J., et al. (författare)
  • Expert Control
  • 1986
  • Ingår i: Automatica. ; 22:3, s. 277-286
  • Tidskriftsartikel (refereegranskat)
6.
  • Astrom, K. J., et al. (författare)
  • Design of decoupled PI controller for two-by-two systems
  • 2002
  • Ingår i: IEE Proceedings - Control Theory and Applications. - IET. - 1350-2379 .- 1359-7035. ; 149:1, s. 74-81
  • Tidskriftsartikel (refereegranskat)abstract
    • The design of PI controllers for systems with interacting loops is discussed. It is advantageous to deal with the interaction at the loop level, because supervisory control seldom has sufficient bandwidth. A new scheme based on modified scalar PI design and static decoupling is developed, in which the frequency characteristic of the coupling between the lower-level loops is taken into account. This leads to a design method emphasising the trade-off between the individual loop performances and the interaction indices introduced in the paper. The controller is easily implemented, due to its simple configuration based on standard components. A useful observation is that the interaction can be reduced substantially by using set-point weighting. The method is applied to three examples, including a model of a new laboratory system called the quadruple-tank process
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10.
  • Färnström, Fredrik, et al. (författare)
  • Computer Vision for determination of Fridge Content
  • 2002
  • Ingår i: Proceedings SSAB'02, Symposium on Image Analysis. - Swedish Society for Automated Image Analysis. ; s. 45-48
  • Konferensbidrag (övrigt vetenskapligt)
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