Blog

• Skeletons and offsetting: A topological point of view

  Update: A conference paper on this topic appeared at EuroCG 2018. Abstract. We investigate topological properties of skeleton structures of shapes like Voronoi diagrams and straight skeletons. We show that these skeleton structures are homotopy-equivalent to the original shape and discuss the homology of skeletons in arbitrary dimensions. Motivated by applications in NC-machining, we investigate offset curves and their evolution and put it into context of persistent homology. One application is the generalization of maximum inscribed circles.

  Posted: Sat, 21 Oct 2017

• Persistent Topology for Peak Detection

  This is a little story of how an abstract mathematical theory like persistent homology can be a practical tool for a usual task in industry.

  Posted: Thu, 28 Sep 2017

• Raspberry Pi Home Server

  This year’s project during xmas vacation was to replace the old Raspberry Pi 1 by a new Raspberry Pi 3 with the official touch display and to increase the functional range.

  Posted: Thu, 05 Jan 2017

• E-Banking in Österreich: Status quo zu TLS & DNSSEC

  Nach etwas mehr als einem Jahr werfen wir erneut einen Blick auf die Sicherheit von E-Banking Internetseiten österreichischer Kreditinstitute in Bezug auf das SSL-Setup und dem Einsatz von DNSSEC.

  Posted: Sat, 28 Mar 2015

• Steuerreform 2015: Lohnsteuer

  Vor wenigen Tagen wurde das Lohnsteuermodell vorgestellt, auf das sich SPÖ und ÖVP geeinigt haben. Im Folgendem wird illustriert, wie sich das Reformmodell vom bisherigen Modell und den ursprünglichen Vorschlägen von SPÖ und ÖVP unterscheidet.

  Posted: Sun, 15 Mar 2015

• Lohnsteuermodelle der SPÖ und ÖVP im Vergleich

  SPÖ und ÖVP haben im Dezember des vergangenen Jahres deren Modellvorschläge für eine Anpassung der Lohnsteuer veröffentlicht. Hier ist der Versuch einer einfachen vergleichenden Analyse.

  Posted: Fri, 23 Jan 2015

• Plots of the data of the SoCG-ACM voting

  Jeff Erickson organized the recent vote for the computational geometry community to decide whether the Symposium on Computational Geometry (SoCG) should stay with ACM or whether it should be organized independently. In addition to asking whether to stay with or leave ACM, he also asked whether one is willing to help organizing SoCG. A few days ago, he presented interesting numerical data of this vote, grouped by country and affiliation of the voters. In the following we present plots from this data.

  Posted: Sun, 20 Jul 2014

• Cryptographic setups of e-banking websites in Austria

  E-banking users rely fundamentally on the security level established by HTTPS connections between their browser and the web server. The actual level of security depends on the proper setup of multiple cryptographic components. In this little survey, we have a look on the different settings of e-banking websites of various banks in Austria.

  Posted: Sun, 16 Feb 2014

• Video surveillance registrations in Austria

  Abstract. Austrian law requires private video surveillance to be registered at the so-called data processing register. Since September 2012 public, anonymous online access is provided to this register. I wrote a little program that requests all datasets from this database and allows one to gain interesting statistical insight into video surveillance registrations in Austria. In particular, I created maps of all video surveillance registrations in Austria.

  Posted: Sat, 18 Jan 2014

• Insecure DNS for internet banking

  The Internet’s domain name service (DNS) was originally designed three decades ago. Back then no security mechanism were included into the specification of DNS, which would guarantee the authenticity of DNS query responses. This deficiency is exploited by widely known DNS cache poisoning and DNS hijacking attacks. DNSSEC is a security extension to DNS, which uses cryptographic signatures in oder to protect against forged DNS data.

  Posted: Sat, 16 Nov 2013

• Voronoi diagram of a convex polyhedron

  In this little blog article, we will show how the Voronoi diagram of a convex polyhedron in -dimensional Euclidean space can be computed in time. As the attentive reader might guess by the time complexity, this is done by intersecting half-spaces in .

  Posted: Wed, 13 Nov 2013

• Brutto- und Netto-Gehälter

  Zu welchem Netto-Zuverdienst führt eine Brutto-Gehaltserhöhung? Steigt das Netto-Gehalt monoton mit dem Brutto-Gehalt? Ist die Steuerbelastung global progressiv? Diesen Fragen wollen wir uns widmen und zu diesem Zweck muss der funktionale Zusammenhang zwischen Brutto- und Nettogehalt erfasst werden.

  Posted: Tue, 28 May 2013

• EGC: a simple case study

  Abstract. This blog article investigates Exact Geometric Computation libraries in general and CORE and LEDA in particular. The starting point is a simple toy problem of testing whether the sum of numbers equals zero and the question whether the way we build the sum significantly influences the runtime and memory costs. The results obtained question the practical implications of complexity analysis w.r.t. the RealRAM model and motivate optimization strategies for EGC libraries. This article also sheds light on runtime, memory and correctness issues that were raised by benchmarks.

  Posted: Thu, 16 May 2013

• The new website is online

  The new website is online. The old one became kind of unhandy and did not fit the requirements anymore. So I decided to give my website a facelift. Well, it turned out to be a bit more. I switched from writing php files by hand to a static website generator, namely Hyde.

  Posted: Mon, 18 Mar 2013