private double Distance(PointF p, LineF line)
{
var p1 = line.Point1;
var p2 = line.Point2;
return(Math.Abs(
((p2.Y - p1.Y) * p.X + (p1.X - p2.X) * p.Y + (p1.Y - p2.Y) * p1.X + (p2.X - p1.X) * p1.Y) /
Math.Sqrt((p2.Y - p1.Y) * (p2.Y - p1.Y) + (p1.X - p2.X) * (p1.X - p2.X))
));
}
private List <PointF> CompressHelper(List <PointF> pointsList, double errorBound)
{
if (pointsList.Count < 2)
{
return(pointsList);
}
var result = new List <PointF>();
// 有可能是polygon
if (pointsList.First().Equals(pointsList.Last()))
{
var r1 = CompressHelper(pointsList.GetRange(0, pointsList.Count / 2), errorBound);
var r2 = CompressHelper(
pointsList.GetRange(pointsList.Count / 2, pointsList.Count - pointsList.Count / 2), errorBound);
result.AddRange(r1);
result.AddRange(r2);
return(result);
}
var line = new LineF(pointsList.First(), pointsList.Last());
double maxDistance = 0;
int maxIndex = 0;
for (int i = 1; i < pointsList.Count - 1; i++)
{
var distance = Distance(pointsList[i], line);
if (distance > maxDistance)
{
maxDistance = distance;
maxIndex = i;
}
}
if (maxDistance <= errorBound)
{
result.Add(pointsList.First());
}
else
{
var r1 = CompressHelper(pointsList.GetRange(0, maxIndex), errorBound);
var r2 = CompressHelper(pointsList.GetRange(maxIndex + 1, pointsList.Count - maxIndex - 1), errorBound);
result.AddRange(r1);
result.Add(pointsList[maxIndex]);
result.AddRange(r2);
}
return(result);
}
