20240422

Core/mapbox-sdk-cs/Utils/PolylineUtils.cs

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+//-----------------------------------------------------------------------
+// <copyright file="PolylineUtils.cs" company="Mapbox">
+//     Copyright (c) 2016 Mapbox. All rights reserved.
+// </copyright>
+//-----------------------------------------------------------------------
+
+namespace Mapbox.Utils
+{
+	using System;
+	using System.Collections.Generic;
+	using System.Text;
+
+	/// <summary>
+	/// A set of Polyline utils.
+	/// </summary>
+	public static class PolylineUtils
+	{
+		/// <summary>Decodes an encoded path string into a sequence of Positions.</summary>
+		/// <remarks>
+		/// Adapted from <see href="https://github.com/mapbox/mapbox-java/blob/9bda93a2f84e26ad67434de1a5c73c335ecac12c/libjava/lib/src/main/java/com/mapbox/services/commons/utils/PolylineUtils.java"/>
+		/// </remarks>
+		/// <param name="encodedPath">A string representing a path.</param>
+		/// <param name="precision">Level of precision. OSRMv4 uses 6, OSRMv5 and Google use 5.</param>
+		/// <returns>List of <see cref="Vector2d"/> making up the line.</returns>
+		public static List<Vector2d> Decode(string encodedPath, int precision = 5)
+		{
+			int len = encodedPath.Length;
+
+			double factor = Math.Pow(10, precision);
+
+			// For speed we preallocate to an upper bound on the final length, then
+			// truncate the array before returning.
+			var path = new List<Vector2d>();
+			int index = 0;
+			int lat = 0;
+			int lng = 0;
+
+			while (index < len)
+			{
+				int result = 1;
+				int shift = 0;
+				int b;
+				do
+				{
+					b = encodedPath[index++] - 63 - 1;
+					result += b << shift;
+					shift += 5;
+				}
+				while (b >= 0x1f);
+				lat += (result & 1) != 0 ? ~(result >> 1) : (result >> 1);
+
+				result = 1;
+				shift = 0;
+				do
+				{
+					b = encodedPath[index++] - 63 - 1;
+					result += b << shift;
+					shift += 5;
+				}
+				while (b >= 0x1f);
+				lng += (result & 1) != 0 ? ~(result >> 1) : (result >> 1);
+
+				path.Add(new Vector2d(y: lng / factor, x: lat / factor));
+			}
+
+			return path;
+		}
+
+		/// <summary>
+		/// Encodes a sequence of Positions into an encoded path string.
+		/// </summary>
+		/// <remarks>
+		/// Adapted from <see href="https://github.com/mapbox/mapbox-java/blob/9bda93a2f84e26ad67434de1a5c73c335ecac12c/libjava/lib/src/main/java/com/mapbox/services/commons/utils/PolylineUtils.java"/>
+		/// </remarks>
+		/// <param name="path">List of <see cref="Vector2d"/> making up the line.</param>
+		/// <param name="precision">Level of precision. OSRMv4 uses 6, OSRMv5 and Google use 5..</param>
+		/// <returns>A string representing a polyLine.</returns>
+		public static string Encode(List<Vector2d> path, int precision = 5)
+		{
+			long lastLat = 0;
+			long lastLng = 0;
+
+			var result = new StringBuilder();
+
+			double factor = Math.Pow(10, precision);
+
+			foreach (Vector2d point in path)
+			{
+				var lat = (long)Math.Round(point.x * factor);
+				var lng = (long)Math.Round(point.y * factor);
+
+				Encode(lat - lastLat, result);
+				Encode(lng - lastLng, result);
+
+				lastLat = lat;
+				lastLng = lng;
+			}
+
+			return result.ToString();
+		}
+
+		/// <summary>
+		/// Encode the latitude or longitude.
+		/// </summary>
+		/// <param name="variable">The value to encode.</param>
+		/// <param name="result">String representation of latitude or longitude.</param>
+		private static void Encode(long variable, StringBuilder result)
+		{
+			variable = variable < 0 ? ~(variable << 1) : variable << 1;
+			while (variable >= 0x20)
+			{
+				result.Append((char)((int)((0x20 | (variable & 0x1f)) + 63)));
+				variable >>= 5;
+			}
+
+			result.Append((char)((int)(variable + 63)));
+		}
+	}
+}