HA 65

A symposium in honor of Helmut Alt's 65th birthday.

When? June, 20 2015, 13:00–18:00
Where? Department of Computer Science, Freie Universität Berlin


We have managed to upload the pictures. You can find them here.


  • 13:00–13:30


  • 13:30–13:35

    Welcome Address

  • 13:35–14:20

    Sue Whitesides

    Helmut Alt, a Perspective from Canada

    Here we review some of the research themes, collaborations, and common interests of Helmut Alt and his Canadian colleagues.
  • 14:25–15:10

    Emo Welzl

    Order on Order Types

    Given P and P', equally sized planar point sets in general position, we call a bijection from P to P' crossing-preserving if crossings of connecting segments in P are preserved in P' (extra crossings may occur in P'). If such a mapping exists, we say that P' crossing-dominates P, and if such a mapping exists in both directions, P and P' are called crossing-equivalent.
    We argue that either the maximal or the minimal point sets are sufficient for answering many combinatorial (existential or extremal) questions on planar point sets. Motivated by this we consider basic properties of the relation.
    (Joint work with Alexander Pilz.)
  • 15:10–15:50

    Cakes, Coffee, and Tea

  • 15:50–16:35

    Maike Buchin

    Many ways to search the Free Space Diagram

    In 1992 Helmut Alt and Michael Godau introduced the Free Space Diagram as a means to compute the Fréchet distance between two polygonal curves. This was the starting point for a long line of research on variants and extensions of the Fréchet distance. In this talk we will focus on different ways of searching the Free Space Diagram in order to compute the classical Fréchet distance. Specifically, we will look at how to search for a unique path in the free space, how to search the free space faster after preprocessing, how to directly search in the so-called Free Space terrain, and how to search the non-free space instead.
  • 16:40–17:10

    Joint presentation by Helmut's students

  • 17:10–17:30

    Closing Words

  • 18:00–???


About Helmut Alt

Helmut Alt was born in 1950 in Wolfersweiler, Saarland. He received his PhD under the supervision of Kurt Mehlhorn from Saarland University in 1976. Helmut Alt is a pioneer of computational geometry and coined the German term “Algorithmische Geometrie.”. Helmut has inspired generations of researchers in Germany and around the world with his work. He was involved in establishing such community forums as the European Workshop on Computational Geometry and the Dagstuhl Workshop on Computational Geometry. Throughout his career, Helmut has advised more than 14 PhD students, many of whom went on to become distinguished scientists.


There is no official registration and no registration fee. However, if you are interested in attending, please write a short e-mail to pseiferth@inf.fu-berlin.de so that we can estimate the number of participants.


The symposium will be held at the Department of Computer Science of Freie Universität Berlin, Takustraße 9, 14195 Berlin. Click here for directions.

To get there (and around in Berlin) we recommend public transportation. You need only one ticket for all kinds of public transport: U-Bahn, S-Bahn, bus, tram, regional trains, and ferry. There is a zone system with three zones (A, B, and C), but it is very unlikely that you will need C. The only two notable exceptions are going to and from Schönefeld Airport and visiting Potsdam. A single ticket costs about 2.70 EUR and a day ticket (Tageskarte) is about 6.90 EUR. Don't forget to stamp the ticket before using it. More on public transport can be found here.

To navigate you can either use the “offline” itineraries at each station or a suitable app (e.g., Google Maps, Öffi, BVG App, etc.). Here are three example connections from the two airports and from the central train station (Hauptbahnhof): Schönefeld Airport → CS Department, Tegel Airport → CS Department, Hauptbahnhof → CS Department.


The Seminaris Hotel is very conveniently located on campus about 3 mins from the department. Please let us book it for you in order to get reduced rates. Otherwise, please book accommodation on your own, e.g., an inexpensive hotel in walking distance (20 mins) is Il Molino. There are also smaller pensions and holiday apartments in the area.

Child Care

We plan to organize a child care service for the Saturday of the symposium. In particular we will hire one (or more, depending on the demand) child minder. If you’re interested in making use of this offer, please write a short mail until April, 26th, 2015 with the number and the approximative age of your children to pseiferth@inf.fu-berlin.de . This will help us making the necessary arrangements.