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berttbertt
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Merge pull request #39 from bertt/copilot/fix-538812-38310808-3ac9b15f-ca6f-4813-b1cc-5c813b410298
Add tile encoder to complement existing decoder
2 parents 8b1a388 + f3b725f commit f563f6f

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‎README.md‎

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[![NuGet Status](http://img.shields.io/nuget/v/mapbox-vector-tile.svg?style=flat)](https://www.nuget.org/packages/mapbox-vector-tile/) ![.NET 8](https://github.com/bertt/mapbox-vector-tile-cs/workflows/.NET%208/badge.svg)
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5-
.NET Standard 2.0 library for decoding a Mapbox vector tile.
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.NET Standard 2.0 library for encoding and decoding Mapbox vector tiles.
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## Dependencies
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## Usage
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### Decoding
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```cs
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const string vtfile = "vectortile.pbf";
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var stream = File.OpenRead(vtfile);
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var layerInfos = VectorTileParser.Parse(stream);
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```
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### Encoding
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```cs
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// Create a layer
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var layer = new VectorTileLayer("my_layer", 2, 4096);
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// Create a feature with attributes and geometry
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var attributes = new List<KeyValuePair<string, object>>
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{
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new KeyValuePair<string, object>("name", "Example"),
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new KeyValuePair<string, object>("value", 42)
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};
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var coordinates = new[] { new Coordinate(100, 200) };
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var geometry = new List<ArraySegment<Coordinate>>
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{
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new ArraySegment<Coordinate>(coordinates)
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};
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var feature = new VectorTileFeature("1", geometry, attributes, Tile.GeomType.Point, 4096);
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layer.VectorTileFeatures.Add(feature);
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// Encode to stream
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var layers = new List<VectorTileLayer> { layer };
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var stream = VectorTileEncoder.Encode(layers, new MemoryStream());
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// Save to file
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File.WriteAllBytes("output.pbf", ((MemoryStream)stream).ToArray());
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```
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Tip: If you use this library with vector tiles loading from a webserver, you could run into the following exception:
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'ProtoBuf.ProtoException: Invalid wire-type; this usually means you have over-written a file without truncating or setting the length'
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Probably you need to check the GZip compression, see also TileParserTests.cs for an example.

‎src/AttributesEncoder.cs‎

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using System;
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using System.Collections.Generic;
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namespace Mapbox.Vector.Tile;
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public static class AttributesEncoder
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{
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public static List<uint> Encode(List<KeyValuePair<string, object>> attributes, List<string> keys, List<Tile.Value> values)
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{
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var tags = new List<uint>();
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foreach (var attribute in attributes)
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{
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var key = attribute.Key;
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var value = attribute.Value;
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// Get or add key index
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var keyIndex = keys.IndexOf(key);
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if (keyIndex == -1)
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{
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keyIndex = keys.Count;
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keys.Add(key);
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}
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// Get or add value index
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var tileValue = CreateTileValue(value);
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var valueIndex = FindValueIndex(values, tileValue);
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if (valueIndex == -1)
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{
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valueIndex = values.Count;
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values.Add(tileValue);
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}
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tags.Add((uint)keyIndex);
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tags.Add((uint)valueIndex);
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}
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return tags;
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}
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private static Tile.Value CreateTileValue(object value)
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{
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var tileValue = new Tile.Value();
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switch (value)
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{
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case string stringValue:
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tileValue.StringValue = stringValue;
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break;
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case bool boolValue:
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tileValue.BoolValue = boolValue;
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break;
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case float floatValue:
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tileValue.FloatValue = floatValue;
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break;
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case double doubleValue:
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tileValue.DoubleValue = doubleValue;
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break;
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case int intValue:
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tileValue.IntValue = intValue;
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break;
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case long longValue:
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tileValue.IntValue = longValue;
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break;
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case uint uintValue:
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tileValue.UintValue = uintValue;
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break;
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case ulong ulongValue:
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tileValue.UintValue = ulongValue;
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break;
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default:
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throw new NotImplementedException($"Unsupported attribute type: {value.GetType()}");
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}
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return tileValue;
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}
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private static int FindValueIndex(List<Tile.Value> values, Tile.Value newValue)
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{
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for (int i = 0; i < values.Count; i++)
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{
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var existingValue = values[i];
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if (ValuesEqual(existingValue, newValue))
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{
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return i;
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}
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}
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return -1;
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}
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private static bool ValuesEqual(Tile.Value a, Tile.Value b)
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{
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if (a.HasStringValue && b.HasStringValue)
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return a.StringValue == b.StringValue;
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if (a.HasBoolValue && b.HasBoolValue)
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return a.BoolValue == b.BoolValue;
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if (a.HasFloatValue && b.HasFloatValue)
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return Math.Abs(a.FloatValue - b.FloatValue) < 0.0001f;
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if (a.HasDoubleValue && b.HasDoubleValue)
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return Math.Abs(a.DoubleValue - b.DoubleValue) < 0.0001;
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if (a.HasIntValue && b.HasIntValue)
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return a.IntValue == b.IntValue;
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if (a.HasSIntValue && b.HasSIntValue)
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return a.SintValue == b.SintValue;
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if (a.HasUIntValue && b.HasUIntValue)
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return a.UintValue == b.UintValue;
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return false;
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}
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}

‎src/GeometryEncoder.cs‎

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using System;
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using System.Collections.Generic;
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using System.Linq;
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namespace Mapbox.Vector.Tile;
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public static class GeometryEncoder
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{
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private enum Command
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{
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MoveTo = 1,
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LineTo = 2,
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ClosePath = 7
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}
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public static List<uint> EncodeGeometry(List<ArraySegment<Coordinate>> geometry, Tile.GeomType geomType)
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{
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var commands = new List<uint>();
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long lastX = 0;
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long lastY = 0;
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foreach (var segment in geometry)
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{
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if (segment.Count == 0)
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continue;
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// Access the underlying array and use offset
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var array = segment.Array!;
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var offset = segment.Offset;
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var count = segment.Count;
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// MoveTo command for first point
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var firstPoint = array[offset];
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commands.Add(EncodeCommand(Command.MoveTo, 1));
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var dx = firstPoint.X - lastX;
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var dy = firstPoint.Y - lastY;
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commands.Add((uint)ZigZag.Encode(dx));
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commands.Add((uint)ZigZag.Encode(dy));
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lastX = firstPoint.X;
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lastY = firstPoint.Y;
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// LineTo commands for remaining points (excluding last if it's a duplicate of first)
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var lineToCount = count - 1;
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// For polygons, check if last point equals first point
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if (geomType == Tile.GeomType.Polygon && count > 1)
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{
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var lastPoint = array[offset + count - 1];
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if (lastPoint.X == firstPoint.X && lastPoint.Y == firstPoint.Y)
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{
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lineToCount--;
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}
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}
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if (lineToCount > 0)
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{
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commands.Add(EncodeCommand(Command.LineTo, (uint)lineToCount));
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for (int i = 1; i <= lineToCount; i++)
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{
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var point = array[offset + i];
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dx = point.X - lastX;
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dy = point.Y - lastY;
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commands.Add((uint)ZigZag.Encode(dx));
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commands.Add((uint)ZigZag.Encode(dy));
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lastX = point.X;
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lastY = point.Y;
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}
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}
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// ClosePath command for polygons only
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if (geomType == Tile.GeomType.Polygon)
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{
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commands.Add(EncodeCommand(Command.ClosePath, 1));
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}
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}
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return commands;
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}
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private static uint EncodeCommand(Command command, uint count)
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{
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return (count << 3) | (uint)command;
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}
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}

‎src/VectorTileEncoder.cs‎

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using ProtoBuf;
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using System.Collections.Generic;
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using System.IO;
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namespace Mapbox.Vector.Tile;
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public static class VectorTileEncoder
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{
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public static Stream Encode(List<VectorTileLayer> layers, Stream stream)
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{
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var tile = new Tile();
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foreach (var vectorTileLayer in layers)
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{
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var layer = new Tile.Layer
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{
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Name = vectorTileLayer.Name,
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Version = vectorTileLayer.Version,
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Extent = vectorTileLayer.Extent
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};
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var keys = new List<string>();
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var values = new List<Tile.Value>();
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foreach (var vectorTileFeature in vectorTileLayer.VectorTileFeatures)
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{
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var feature = new Tile.Feature
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{
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Id = ulong.Parse(vectorTileFeature.Id),
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Type = vectorTileFeature.GeometryType
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};
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// Encode attributes
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var tags = AttributesEncoder.Encode(vectorTileFeature.Attributes, keys, values);
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feature.Tags.AddRange(tags);
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// Encode geometry
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var geometry = GeometryEncoder.EncodeGeometry(vectorTileFeature.Geometry, vectorTileFeature.GeometryType);
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feature.Geometry.AddRange(geometry);
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layer.Features.Add(feature);
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}
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layer.Keys.AddRange(keys);
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layer.Values.AddRange(values);
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tile.Layers.Add(layer);
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}
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Serializer.Serialize(stream, tile);
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return stream;
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}
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}

‎tests/RealTileRoundTripTest.cs‎

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using Mapbox.Vector.Tile;
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using NUnit.Framework;
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using System.IO;
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namespace mapbox.vector.tile.tests;
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public class RealTileRoundTripTest
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{
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[Test]
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public void TestRealTileRoundTrip()
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{
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// Test that we can decode a real tile and encode it back
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var pbfFile = Path.Combine("testdata", "14-8801-5371.vector.pbf");
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// Decode the original tile
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var originalStream = File.OpenRead(pbfFile);
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var decodedLayers = VectorTileParser.Parse(originalStream);
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originalStream.Close();
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Assert.That(decodedLayers.Count, Is.GreaterThan(0), "Should have decoded at least one layer");
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// Encode it back
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var encodedStream = new MemoryStream();
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VectorTileEncoder.Encode(decodedLayers, encodedStream);
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encodedStream.Seek(0, SeekOrigin.Begin);
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Assert.That(encodedStream.Length, Is.GreaterThan(0), "Encoded stream should not be empty");
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// Decode the encoded tile
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var reDecodedLayers = VectorTileParser.Parse(encodedStream);
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// Verify layer count matches
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Assert.That(reDecodedLayers.Count, Is.EqualTo(decodedLayers.Count), "Layer count should match");
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// Verify each layer
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for (int i = 0; i < decodedLayers.Count; i++)
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{
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var original = decodedLayers[i];
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var reDecoded = reDecodedLayers[i];
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Assert.That(reDecoded.Name, Is.EqualTo(original.Name), $"Layer {i} name should match");
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Assert.That(reDecoded.VectorTileFeatures.Count, Is.EqualTo(original.VectorTileFeatures.Count),
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$"Layer '{original.Name}' feature count should match");
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}
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}
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}

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