11 papers
Bivariate quaternionic factorizations and surfaces that decompose into two circles
Johanna Frischauf, Niels Lubbes, Hans-Peter Schröcker
We present an algebraic and geometric condition for bivariate quaternionic polynomials of arbitrary bidegree to have a univariate linear left or right factor. We apply this quatern…
Self-intersections of surfaces that contain two circles through each point
Niels Lubbes
We classify the singular loci of real surfaces in three-space that contain two circles through each point. We characterize how a circle in such a surface meets this loci as it move…
Irreducible components of sets of points in the plane that satisfy distance conditions
Niels Lubbes, Mehdi Makhul, Josef Schicho +1
For a given graph whose edges are labeled with general real numbers, we consider the set of functions from the vertex set into the Euclidean plane such that the distance between th…
Calibrating Figures
Niels Lubbes, Josef Schicho
It is known that a camera can be calibrated using three pictures of either squares, spheres, or surfaces of revolution. We give a new method to calibrate a camera with the picture…
Calligraphs and sphere realizations
Matteo Gallet, Georg Grasegger, Niels Lubbes +1
We introduce a recursive procedure for computing the number of realizations of a minimally rigid graph on the sphere up to rotations. We accomplish this by combining two ingredient…
Reconstruction of surfaces with ordinary singularities from their silhouettes
Matteo Gallet, Niels Lubbes, Josef Schicho +1
We present algorithms for reconstructing, up to unavoidable projective automorphisms, surfaces with ordinary singularities in three dimensional space starting from their silhouette…