Graph Drawing Live Challenge

Upward drawings on a fixed grid

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 will be two categories in the challenge that are judged independently:

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 only to change vertex locations. This category is for creating manual solutions without help of an automatic algorithm. Teams in this category will receive smaller challenge graphs. The tool is available in the submission system.

The challenge focuses on minimizing the number of crossings in a straight-line upward drawing on a fixed grid. The input graphs are directed graphs without directed cycles.

A straight-line upward drawing is a drawing in which each directed edge is represented as a line segment such that the target vertex has a strictly higher y-coordinate than the source vertex. Two edges of an embedded graph are said to cross if they do not share an endpoint, but the interiors of their images intersect. The goal is to find a straight-line upward drawing which minimizes the number of crossings.

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 up to three participants each. Each team should 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.
At the start of the challenge, contestants will receive a collection of five to ten graphs. The graphs will have up to a few thousand nodes.
The allowed grid size will be specified in the file format, but will not be larger than 1,000,000 x 1,000,000.
For each graph, the team submitting the drawing with the smallest number of crossings receives the highest score. The graphs do not necessarily have an initial embedding.
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.

File Format

For the GD2020 contest, a JSON format described below will be used. The contest graphs will be provided in this format and the final submissions should be prepared using the same format. A valid JSON file consists of the following entries:

nodes: An array with one element per node of the graph. Each element has the following entries:
- id: The id of the node. Has to be an integer between 0 and #nodes-1.
- x: The x-coordinate of the node. Has to be an integer between 0 and width.
- y: The y-coordinate of the node. Has to be an integer between 0 and height.
edges: An array with one element per edge of the graph. Each element has the following entries:
- source: The id of the source node.
- target: The id of the target node.
width (optional): The maximum x-coordinate of the grid. Has to be a non-negative integer. If unspecified, the width is set to 1,000,000.
height (optional): The maximum y-coordinate of the grid. Has to be a non-negative integer. If unspecified, the height is set to 1,000,000.

Sample File

Below is a simple example:

{ "nodes": [
    { "id": 0, "x": 1, "y": 0 },
    { "id": 1, "x": 1, "y": 1 },
    { "id": 2, "x": 2, "y": 1 },
    { "id": 3, "x": 0, "y": 2 },
    { "id": 4, "x": 2, "y": 2 }],
  "edges": [
    { "source": 0, "target": 1 },
    { "source": 0, "target": 2 },
    { "source": 0, "target": 3 },
    { "source": 1, "target": 4 },
    { "source": 2, "target": 3 }],
  "width": 2,
  "height": 2 }

The left drawing below corresponds to this input file. This layout has on crossing and is not optimal. By moving the nodes 1 and 4 to the left and the node 3 to the right, the graph can be drawn crossing-free; see the middle drawing below. The right drawing is also crossing-free, but it is invalid as the edge between nodes 0 and 3 as well as the edge between nodes 2 and 3 are not upward.

How to participate

The Live Challenge will be part of the 28th International Symposium on Graph Drawing and Network Visualization, and will take place on September 15, 2020, 09:00 PDT (16:00 UTC, 18:00 CEST), this year completely remotely.

Please join us in gather.town for hanging out, forming teams, getting instructions, and asking questions. We will give a brief introduction to the tool 10 minutes before the start of the challenge.

If you wish to participate in the manual category, you will attempt to solve the problems using a supplied tool.

If you wish to participate in the automatic category, you can use any software you wish to solve the problems, including the supplied tool (however, problems instances will be much larger than in the manual category).

You may use at most one computer per team.

The challenge will be run through an online submission system. You can already visit the system and try out some test graphs.