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Statistics of shape, direction and cylindrical variables. (English) Zbl 1121.62434

Summary: In statistical shape analysis, the shape of an object is understood to be what remains after the effects of location, scale and rotation are removed. We consider the distributional problem of triangular shape and an associated direction; motivated by a data set of microscopic fossils. We begin by constructing a parallel transport system such that the data transform onto the space \(\mathbb S^{2} \times \mathbb S^{2}\). A joint shape distribution on \(\mathbb S^{2} \times \mathbb S^{1}\) is proposed based on Jupp & Mardia’s bivariate distribution on \(\mathbb S^{2} \times \mathbb S^{1}\). For concentrated data, an approximation to the distribution on \(\mathbb S^{2} \times \mathbb S^{1}\) is given by a distribution on \(\mathbb R^{1} \times \mathbb S^{1}\), and we explore a distribution on this space by extending Mardia & Sutton’s distribution on \(\mathbb R^{2} \times \mathbb S^{1}\). In this distribution, the expected edgel direction varies linearly in the shape coordinates. This is found to be a useful model for the microfossil data.

MSC:

62-XX Statistics
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