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Posted 10 Aug 2005


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Fortune's Voronoi algorithm implemented in C#

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2.91/5 (30 votes)
21 Apr 2013MPL2 min read
A C# implementation of the Fortune algorithm to compute 2D Voronoi graphs.

NOTE: Code has moved to Google Code! 


Given a set of two dimensional vectors (or data points), a Voronoi graph is a separation of those points into compartments where all points inside one compartment are closer to the contained data point than to any other data point. I won't give any demonstration here, but if you want to know more about Voronoi graphs, check out this.

The applications of Voronoi graphs are quite broad. Very useful for a lot of optimization problems (in most cases, the Delaunay Triangulation which can be easily derived from a Vononoi graph is used there), it ranges to computing topological maps from bitmaps.

[This is an article for freaks. After a rather painful experience writing the thing I hope it will benefit everyone who is looking for this algorithm in a civilized language (or simply does not want to use Fortune's original C implementation).]

In 1987, Steve Fortune described an algorithm to compute such a graph by using a sweep line in combination with a binary tree. A PowerPoint explanation of the algorithm (the one I used to implement it) can be found here. Note that I did not use the linked data structure to represent a graph - I think that is an unnecessary difficulty in the age of ArrayLists and HashSets.

The Implementation

Data points are represented by my own Vector class. It can do much more than needed here (but there was no reason to strip it before bringing it) but I won't explain it here. The most important fact is that although working with doubles the Vector class automatically rounds values to 10 digits (or whatever is set in the Vector.Precision field). Yes, sadly, this is very important if you want to sort of compare doubles.

A VoronoiGraph is a class that only contains a HashSet of vertices (as 2D vectors) and a HashSet of VoronoiEdges - each with references to the left and right data point and (of course) the two vertices that bound the edge. If the edge is (partially or completely) unbounded, the vector Fortune.VVUnknown is used.

BinaryPriorityQueue is used for the sweep line event queue.


The algorithm itself (Fortune.ComputeVoronoiGraph(IEnumerable)) takes any IEnumerable containing only two dimensional vectors. It will return a VoronoiGraph. The algorithm's complexity is O(n ld(n)) with a factor of about 10 microseconds on my machine (2GHz).


This article, along with any associated source code and files, is licensed under The Mozilla Public License 1.1 (MPL 1.1)

Written By
Software Developer (Senior)
Germany Germany
I did my diploma in Dresden and Sydney where I dealt with algorithms, agents and other cool AI stuff. Now I moved to Frankfurt to work on my PhD dealing with software structures for artificial intelligence systems. If I can, I do things in C# and ASP.NET, but if I have to, my C++, Java and SQL are not that bad.
Long Live .NET.

Comments and Discussions

QuestionUpdate license Pin
Vermillion Wizard15-Jul-18 6:30
MemberVermillion Wizard15-Jul-18 6:30 
Questionan error with fortune's sweepline Pin
Member 1358600019-Dec-17 22:04
MemberMember 1358600019-Dec-17 22:04 
QuestionThe link has been invalid,would you send it to my e-mail Pin
Member 1194025111-Jul-16 7:28
MemberMember 1194025111-Jul-16 7:28 
QuestionCode exported to github for storing purposes, as google-code ceases to exist Pin
Bartosz Nowak10-Sep-15 10:41
MemberBartosz Nowak10-Sep-15 10:41 
GeneralMy vote of 5 Pin
Kristian Lindberg Vinther9-Jan-15 10:42
professionalKristian Lindberg Vinther9-Jan-15 10:42 
QuestionInteresting Pin
Member 1083802822-May-14 12:58
MemberMember 1083802822-May-14 12:58 
AnswerRe: Interesting Pin
Kristian Lindberg Vinther5-Jan-15 5:32
professionalKristian Lindberg Vinther5-Jan-15 5:32 
QuestionHow to get a Polygon list asociated to seed Points Pin
marceloarguello70012-Jan-14 10:17
Membermarceloarguello70012-Jan-14 10:17 
QuestionSmall example code would be very much appreciated Pin
pan05417-Dec-13 5:20
Memberpan05417-Dec-13 5:20 
Questionvoronoy bad link Pin
Giovanni Cuccureddu21-Sep-13 22:22
MemberGiovanni Cuccureddu21-Sep-13 22:22 
Questiondivide and conquer . Pin
rizikandry23-Jul-13 4:02
Memberrizikandry23-Jul-13 4:02 
QuestionMESSAGE FROM THE OWNER: Help improve this project on Google Code! Pin
BenDi21-Apr-13 7:59
MemberBenDi21-Apr-13 7:59 
QuestionRounding error when creating circles for new nodes Pin
Bwd Yeti19-Apr-13 1:50
MemberBwd Yeti19-Apr-13 1:50 
AnswerRe: Rounding error when creating circles for new nodes Pin
BenDi21-Apr-13 7:56
MemberBenDi21-Apr-13 7:56 
QuestionDon't know where to start Pin
Member 998975818-Apr-13 17:58
MemberMember 998975818-Apr-13 17:58 
GeneralMy vote of 4 Pin
PehGuevara7-Mar-13 22:40
MemberPehGuevara7-Mar-13 22:40 
QuestionGetting regions from graph Pin
Bixel6-Feb-13 15:14
MemberBixel6-Feb-13 15:14 
AnswerRe: Getting regions from graph Pin
BenDi7-Feb-13 0:50
MemberBenDi7-Feb-13 0:50 
GeneralRe: Getting regions from graph Pin
Bixel7-Feb-13 13:06
MemberBixel7-Feb-13 13:06 
QuestionSeparating braches of a medial axis sampled from inner voronoi points of a polygon Pin
Member 917583217-Jul-12 17:19
MemberMember 917583217-Jul-12 17:19 
QuestionFinding distance for VoronoiGraph vertizes representing Medial Axis of closed boundary Pin
Member 917583214-Jul-12 6:02
MemberMember 917583214-Jul-12 6:02 
GeneralRe: Finding distance for VoronoiGraph vertizes representing Medial Axis of closed boundary Pin
BenDi15-Jul-12 1:27
MemberBenDi15-Jul-12 1:27 
AnswerRe: Finding distance for VoronoiGraph vertizes representing Medial Axis of closed boundary Pin
Kenneth Haugland17-Jul-12 10:31
mvaKenneth Haugland17-Jul-12 10:31 
GeneralRe: Finding distance for VoronoiGraph vertizes representing Medial Axis of closed boundary Pin
Member 917583217-Jul-12 17:11
MemberMember 917583217-Jul-12 17:11 
QuestionIs there a way to construct polygons from all the edges ? And how ? Pin
seb.493-Jun-12 22:36
Memberseb.493-Jun-12 22:36 

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