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**Convergence of algorithms for reconstructing convex bodies and directional measures.**
*(English)*
Zbl 1097.52503

Summary: We investigate algorithms for reconstructing a convex body \(K\) in \(\mathbb R^n\) from noisy measurements of its support function or its brightness function in \(k\) directions \(u_1,\dots,u_k\). The key idea of these algorithms is to construct a convex polytope \(P_k\) whose support function (or brightness function) best approximates the given measurements in the directions \(u_1,\dots,u_k\) (in the least squares sense). The measurement errors are assumed to be stochastically independent and Gaussian.

It is shown that this procedure is (strongly) consistent, meaning that, almost surely, \(P_k\) tends to \(K\) in the Hausdorff metric as \(k\to\infty\). Here some mild assumptions on the sequence \((u_i)\) of directions are needed. Using results from the theory of empirical processes, estimates of rates of convergence are derived, which are first obtained in the \(L_2\) metric and then transferred to the Hausdorff metric. Along the way, a new estimate is obtained for the metric entropy of the class of origin-symmetric zonoids contained in the unit ball.

Similar results are obtained for the convergence of an algorithm that reconstructs an approximating measure to the directional measure of a stationary fiber process from noisy measurements of its rose of intersections in \(k\) directions \(u_1,\dots,u_k\). Here the Dudley and Prohorov metrics are used. The methods are linked to those employed for the support and brightness function algorithms via the fact that the rose of intersections is the support function of a projection body.

It is shown that this procedure is (strongly) consistent, meaning that, almost surely, \(P_k\) tends to \(K\) in the Hausdorff metric as \(k\to\infty\). Here some mild assumptions on the sequence \((u_i)\) of directions are needed. Using results from the theory of empirical processes, estimates of rates of convergence are derived, which are first obtained in the \(L_2\) metric and then transferred to the Hausdorff metric. Along the way, a new estimate is obtained for the metric entropy of the class of origin-symmetric zonoids contained in the unit ball.

Similar results are obtained for the convergence of an algorithm that reconstructs an approximating measure to the directional measure of a stationary fiber process from noisy measurements of its rose of intersections in \(k\) directions \(u_1,\dots,u_k\). Here the Dudley and Prohorov metrics are used. The methods are linked to those employed for the support and brightness function algorithms via the fact that the rose of intersections is the support function of a projection body.

### MSC:

52A20 | Convex sets in \(n\) dimensions (including convex hypersurfaces) |

62M30 | Inference from spatial processes |

65D15 | Algorithms for approximation of functions |

52A21 | Convexity and finite-dimensional Banach spaces (including special norms, zonoids, etc.) (aspects of convex geometry) |

60D05 | Geometric probability and stochastic geometry |

60G10 | Stationary stochastic processes |

### Keywords:

convex body; convex polytope; support function; brightness function; surface area measure; least squares; set-valued estimator; cosine transform; algorithm; geometric tomography; stereology; fiber process; rose of intersections
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\textit{R. J. Gardner} et al., Ann. Stat. 34, No. 3, 1331--1374 (2006; Zbl 1097.52503)

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