I have found multiple implementations of the Douglas-Peucker algorithm but not in any .NET language, so I decided to port it over. Jonathan de Halleux has a wonderful explanation here.
I needed to reduce polygons size to display on a map based on zoom levels.
Using the Code
The code included is complete and should run out of the box in Visual Studio 2005. If it does not, please let me know.
public static List<Point> DouglasPeuckerReduction
(List<Point> Points, Double Tolerance)
if (Points == null || Points.Count < 3)
Int32 firstPoint = 0;
Int32 lastPoint = Points.Count - 1;
List<Int32> pointIndexsToKeep = new List<Int32>();
DouglasPeuckerReduction(Points, firstPoint, lastPoint,
Tolerance, ref pointIndexsToKeep);
List<Point> returnPoints = new List<Point>();
foreach (Int32 index in pointIndexsToKeep)
private static void DouglasPeuckerReduction(List<Point>
points, Int32 firstPoint, Int32 lastPoint, Double tolerance,
ref List<Int32> pointIndexsToKeep)
Double maxDistance = 0;
Int32 indexFarthest = 0;
for (Int32 index = firstPoint; index < lastPoint; index++)
Double distance = PerpendicularDistance
(points[firstPoint], points[lastPoint], points[index]);
if (distance > maxDistance)
maxDistance = distance;
indexFarthest = index;
if (maxDistance > tolerance && indexFarthest != 0)
indexFarthest, tolerance, ref pointIndexsToKeep);
lastPoint, tolerance, ref pointIndexsToKeep);
public static Double PerpendicularDistance
(Point Point1, Point Point2, Point Point)
Double area = Math.Abs(.5 * (Point1.X * Point2.Y + Point2.X *
Point.Y + Point.X * Point1.Y - Point2.X * Point1.Y - Point.X *
Point2.Y - Point1.X * Point.Y));
Double bottom = Math.Sqrt(Math.Pow(Point1.X - Point2.X, 2) +
Math.Pow(Point1.Y - Point2.Y, 2));
Double height = area / bottom * 2;
Points of Interest
The code is not overly complicated. It was fun to port this algorithm, since all I feel I do nowadays is hold business' hands to help them try and solve business problems that there is no consensus on.
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