GD Challenge: Orthogonal layout with minimal longest edge

We shall hold the Graph Drawing Challenge in a format similar to a typical programming contest. At the start of the challenge, teams of contestants will receive the collection of challenge-graphs. After one hour, the teams will submit their final drawings and the team with the highest cumulative score wins.

Teams will be allowed to use any combination of software and human interaction systems to produce the best drawings. To accommodate both teams wishing to prepare for the challenge and teams wishing simply to participate, with no preparation, we will be providing, in advance, a small set of graph visualization tools. These tools are not necessarily meant to solve the problems at hand but are there to help the teams manually draw and manipulate the graphs. To further the development of new tools and to help promote tools already in existence, teams are also welcome and highly encouraged to create and bring their own software packages.

There exist two categories in the challenge that are judged separately.

  • Automatic - This category is for teams using their own tool. Since we assume that the tool contains special algorithms to solve the challenge automatically, these teams will receive larger challenge graphs. Manual fine-tuning is allowed.
  • Manual - This category is for teams using the provided graph editor. The graph editor does not contain any specific algorithm to solve the challenge. It allows one only to move nodes and to re-route edges. This category is for creating manual solutions without help of an automatic algorithm. Teams in this category will receive smaller challenge graphs.

Following the Graph Drawing Contest tradition, we repeat the same challenge as in year 2010. (For 2012, a new challenge is planned.) The challenge focuses on minimizing the length of the longest edge in a planar orthogonal layout. The challenge graphs will be planar and 4-ary (maximally 4 incident edges per node). Nodes have no dimension, they can essentially be considered as points. All drawings must have the following properties:

  • All nodes and edge bends are placed on distinct integer grid coordinates.
  • Edges must be routed orthogonally, that is, they must consist of segments that are stictly horizontal or strictly vertical.
  • Edge crossings are not allowed: the layout must be planar.
  • Node and edge overlaps are forbidden; in particular, it is not allowed that edges touch each other (except for common endpoints), and that edges touch nodes other than their endpoints.
  • There is no limit on the number of bends.
  • The length of an edge is the sum of its segment lengths.
  • The length of the longest edge of the layout is the only scoring criteria. We are looking for the layout that has the smallest longest edge.

The results are judged solely with respect to the length of the longest edge. The other edges, except the longest edge, are not taken into account for the score. Other aesthetic criteria are also not taken into account. This allows an objective way to evaluate a given drawing qualitatively.

Here is an overview of the rules for the challenge:

  • The challenge will take place for one hour during the Graph Drawing Symposium.
  • Teams may consist of one to three participants each. Each team may bring their own computers and/or software tools to the challenge.
  • Software tools for manually solving the challenge will be provided for each team with time available prior to the challenge to set-up and practice with the system. There will also be computers available with the software already installed.
  • At the start of the challenge, contestants will receive a collection of five to ten graphs. The graphs will be planar with twenty to a few thousand nodes.
  • The graphs will have an initial, planar orthogonal layout. In order to produce the result, the embedding is allowed to be changed.
  • For each graph, the team submitting the drawing with the smallest longest edge receives the highest score. Scores for other submissions of the same graph shall be weighed with respect to this value. The team with the highest total score over all graphs wins.

Remote participation

For those teams that cannot attend the conference but still wish to compete (in the automatic category), we allow remote participation. A few key points:

  • Participants should contact the committee prior to the contest (no later than September 15, 2011), and preferably as early as possible, to help determine the number of remote teams and to coordinate the instructions.
  • At the time of the challenge, remote teams will be able to access an online location (website) to download the data sets and then simply submit the results via email.
  • Detailed submission instructions will be provided on this site at a later time.

File format

For the GD2011 contest, an ASCII format described below will be used. It is the same format that was used in GD2010. The contest graphs will be provided in this format and the final submissions should be prepared using the same format.

  • The first number (N) indicates the number of nodes in the graph.
  • The next 2N numbers contain the coordinates of the nodes. Each coordinate consists of the x and the y value of the node, indicating its position.
  • The remainder of the file contains the edges. For each edge, the first value is the index of the source node, and the second value is the index of the target node. Next follows an array with an even number of values, enclosed by [ ... ], which are the x and y coordinates of the bend points of the edge.
  • An edge that has no bend points is written as an empty bend array [].
  • The nodes are labeled from 0 to N-1 and the order from the input file must be used in the output file as well.
  • Comments are allowed as indicated below.
  • The edge order is not important.
  • The contest graphs will have random start locations for the nodes.
  • All numbers are integers.

Sample file

Below is a simple example:

# Lines starting with # are comments and ignored
# First value is NumNodes(N)
# Next N pairs are x and y coordinate values of each node
4 2  # Node 0
2 4  # Node 1
4 4  # Node 2
6 4  # Node 3
4 6  # Node 4
# Remaining lines are the edges.
# The first value is the source node.
# The second value is the target node.
# The values between [ ... ] are grouped in pairs as bend points (X,Y)
1 0 [ 2 2 ]             # Edge between Node 1 and Node 0 with bend point (2,2)
0 3 [ 6 2 ]             # Edge between Node 0 and Node 3 with bend point (6,2)
2 1 []                  # Edge between Node 2 and Node 1 with no bend points
2 3 []                  # Edge between Node 2 and Node 3 with no bend points
0 2 []                  # Edge between Node 0 and Node 2 with no bend points
1 4 [ 2 6 ]             # Edge between Node 1 and Node 4 with bend point (2,6)
4 3 [ 6 6 ]             # Edge between Node 4 and Node 3 with bend point (6,6)
0 4 [ 4 0 0 0 0 8 4 8 ] # Edge with bend points (4,0), (0,0), (0,8) and (4,8)

The diagram below corresponds to this input file. This layout is not optimal, since it can be compressed so that the longest edge gets shorter. The longest edge is the one between node 0 and node 4. It has the length 20, since it has two segments of length 2, two segments of length 4 and one segment of length 8.

Last year's sample files

Since this is the same challenge as at GD 2010, we provide here the software and the files of the challenge graphs that were used in 2010. These specific graphs, clearly, will not be used in the GD 2011 Challenge. They are only provided as samples. Next to each file link, we are providing the best submitted manual solution, and where available, the optimal solution for the graph. The best submitted automatic solutions are unfortunately only available as a screenshot. Note that "Manual Category Problem 4" and "Automatic Category Problem 1" are the same, as well as "Manual Category Problem 5" and "Automatic Category Problem 2". For "Manual Category Problem 6", we know a better solution than the best submitted solution, but it has not been proven that this solution is optimal.

The software that was used in 2010 for the Manual Category can be downloaded here. To start the program, double click on the jar file, or use java -jar gd2010.jar. This software can be used to view the graphs or for training purposes. However, in 2011, we will provide updated software, which might have differences with the 2010 version.

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Graph Drawing 2011