Indexing involves identifying Bragg spots (reflections) observed in frames containing a diffraction pattern and using them to infer the crystal orientation. The process begins by mapping the positions of Bragg spots on the detector to a set of vectors in three-dimensional reciprocal space lying on the Ewald sphere . Such mapping can be computed based on the experimental setup (i.e., detector geometry, position of the sample, wavelength and incident direction of beam, etc). The resulting set of points in three-dimensional reciprocal space, denoted as Q, is a subset of a rotated version of the reciprocal lattice which is initially unknown. We refer to the points in Q as reciprocal spots. We formalize the mathematical problem of indexing a set of points Q in reciprocal space.