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70 lines
1.4 KiB
70 lines
1.4 KiB
namespace Mapbox.Utils
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{
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using System.Collections.Generic;
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using Mapbox.VectorTile.Geometry;
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public static class PolygonUtils
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{
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/// <summary>
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/// <para>Method to check if a point is contained inside a polygon, ignores vertical axis (y axis)</para>
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/// <para>from https://stackoverflow.com/a/7123291</para>
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/// </summary>
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/// <returns><c>true</c>, if point lies inside the constructed polygon, <c>false</c> otherwise.</returns>
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/// <param name="polygon">Polygon points.</param>
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/// <param name="p">The point that is to be tested.</param>
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public static bool PointInPolygon(Point2d<float> p, List<List<Point2d<float>>> polygon)
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{
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List<Point2d<float>> poly = polygon[0];
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Point2d<float> p1;
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Point2d<float> p2;
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bool inside = false;
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if (poly.Count < 3)
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{
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return inside;
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}
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var oldPoint = new Point2d<float>(
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poly[poly.Count - 1].X
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, poly[poly.Count - 1].Y
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);
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for (int i = 0; i < poly.Count; i++)
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{
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var newPoint = new Point2d<float>(poly[i].X, poly[i].Y);
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if (newPoint.X > oldPoint.X)
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{
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p1 = oldPoint;
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p2 = newPoint;
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}
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else
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{
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p1 = newPoint;
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p2 = oldPoint;
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}
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if (
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(newPoint.X < p.X) == (p.X <= oldPoint.X)
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&& (p.Y - (long)p1.Y) * (p2.X - p1.X) < (p2.Y - (long)p1.Y) * (p.X - p1.X)
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)
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{
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inside = !inside;
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}
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oldPoint = newPoint;
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}
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return inside;
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}
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}
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}
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