Discrete tomography:

Determination of finite sets by X-rays

Authors:
R. J. Gardner and Peter Gritzmann

Journal:
Trans. Amer. Math. Soc. **349** (1997), 2271-2295

MSC (1991):
Primary 52C05, 52C07; Secondary 52A20, 52B20, 68T10, 68U05, 82D25, 92C55

MathSciNet review:
1376547

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Abstract | References | Similar Articles | Additional Information

Abstract: We study the determination of finite subsets of the integer lattice , , by X-rays. In this context, an X-ray of a set in a direction gives the number of points in the set on each line parallel to . For practical reasons, only X-rays in lattice directions, that is, directions parallel to a nonzero vector in the lattice, are permitted. By combining methods from algebraic number theory and convexity, we prove that there are four prescribed lattice directions such that convex subsets of (i.e., finite subsets with ) are determined, among all such sets, by their X-rays in these directions. We also show that three X-rays do not suffice for this purpose. This answers a question of Larry Shepp, and yields a stability result related to Hammer's X-ray problem. We further show that any set of seven prescribed mutually nonparallel lattice directions in have the property that convex subsets of are determined, among all such sets, by their X-rays in these directions. We also consider the use of orthogonal projections in the interactive technique of successive determination, in which the information from previous projections can be used in deciding the direction for the next projection. We obtain results for finite subsets of the integer lattice and also for arbitrary finite subsets of Euclidean space which are the best possible with respect to the numbers of projections used.

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Additional Information

**R. J. Gardner**

Affiliation:
Department of Mathematics, Western Washington University, Bellingham, Washington 98225-9063

Email:
gardner@baker.math.wwu.edu

**Peter Gritzmann**

Affiliation:
Fb IV, Mathematik, Universität Trier, D-54286 Trier, Germany

Email:
gritzman@dm1.uni-trier.de

DOI:
http://dx.doi.org/10.1090/S0002-9947-97-01741-8

Keywords:
Tomography,
discrete tomography,
X-ray,
projection,
lattice,
lattice polygon,
convex body,
$p$-adic valuation

Received by editor(s):
October 3, 1995

Additional Notes:
First author supported in part by the Alexander von Humboldt Foundation and by National Science Foundation Grant DMS-9501289; second author supported in part by the Deutsche Forschungsgemeinschaft and by a Max Planck Research Award.

Article copyright:
© Copyright 1997
American Mathematical Society