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Direct derivations of certain surface integral formulae for the mean projections of a convex set

Published online by Cambridge University Press:  01 July 2016

R. E. Miles
R. E. Miles*
Affiliation:
The Australian National University, Canberra
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Abstract

A simple direct proof is given of Minkowski's result that the mean length of the orthogonal projection of a convex set in E3 onto an isotropic random line is (2π)–1 times the integral of mean curvature over its surface. This proof is generalised to a correspondingly direct derivation of an analogous formula for the mean projection of a convex set in En onto an isotropic random s-dimensional subspace in En. (The standard derivation of this, and a companion formula, to be found in Bonnesen and Fenchel's classic book on convex sets, is most indirect.) Finally, an alternative short inductive derivation (due to Matheron) of both formulae, by way of Steiner's formula, is presented.

Keywords

GEOMETRICAL PROBABILITYINTEGRAL GEOMETRYSTEREOLOGYISOTROPIC RANDOM SUBSPACEMEAN PROJECTIONQUERMASSINTEGRALCONVEX SETMIXED VOLUMESURFACE INTEGRAL
Type
Research Article
Information
Advances in Applied Probability , Volume 7 , Issue 4 , December 1975 , pp. 818 - 829
Copyright
Copyright © Applied Probability Trust 1975 

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