| 1. |
- Bergström, Per, et al.
(författare)
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Robust registration of surfaces using a refined iterative closest point algorithm with a trust region approach
- 2017
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Ingår i: Numerical Algorithms. - : Springer. - 1017-1398 .- 1572-9265. ; 74:3, s. 755-779
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Tidskriftsartikel (refereegranskat)abstract
- The problem of finding a rigid body transformation, which aligns a set of data points with a given surface, using a robust M-estimation technique is considered. A refined iterative closest point (ICP) algorithm is described where a minimization problem of point-to-plane distances with a proposed constraint is solved in each iteration to find an updating transformation. The constraint is derived from a sum of weighted squared point-to-point distances and forms a natural trust region, which ensures convergence. Only a minor number of additional computations are required to use it. Two alternative trust regions are introduced and analyzed. Finally, numerical results for some test problems are presented. It is obvious from these results that there is a significant advantage, with respect to convergence rate of accuracy, to use the proposed trust region approach in comparison with using point-to-point distance minimization as well as using point-to-plane distance minimization and a Newton- type update without any step size control.
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| 2. |
- Michelson, Ingrid H., et al.
(författare)
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Autumn senescence in aspen is not triggered by day length
- 2018
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Ingår i: Physiologia Plantarum. - : John Wiley & Sons. - 0031-9317 .- 1399-3054. ; 162:1, s. 123-134
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Tidskriftsartikel (refereegranskat)abstract
- Autumn senescence in mature aspens, grown under natural conditions, is initiated at almost the same date every year. The mechanism of such precise timing is not understood but we have previously shown that the signal must be derived from light. We studied variation in bud set and autumn senescence in a collection of 116 natural Eurasian aspen (Populus tremula) genotypes, from 12 populations in Sweden and planted in one northern and one southern common garden, to test the hypothesis that onset of autumn senescence is triggered by day length. We confirmed that, although bud set seemed to be triggered by a critical photoperiod/day length, other factors may influence it. The data on initiation of autumn senescence, on the other hand, were incompatible with the trigger being the day length per se, hence the trigger must be some other light-dependent factor.
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