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A package that can be used to generate vector tiles using NTS.
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A package that can be used to read or generate vector tiles using NTS.
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## Getting started
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This package is still experimental and does not yet have a NuGet package. To load this package into your app, download the source code, copy all three projects into your solution folder. Then within Visual Studio use the *"Add Existing Project"* option to add these to your solution. From there, you can use the *"Add Project References"* function in Visual Studio to bring this functionality into your app.
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### Create a vector tile
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The following shows how to create an individual vector tile, pass in a Feature from NTS, and write the tile as a file.
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```csharp
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//Define which tile you want to create.
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vartileDefinition=newNetTopologySuite.IO.VectorTiles.Tiles.Tile(x, y, zoom);
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//Create a vector tile instance and pass om the tile ID from the tile definition above.
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varvt=newVectorTile { TileId=tileDefinition.id };
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//Create one or more layers. Ideally one layer per dataset.
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varlyr=newLayer { Name="layer1" };
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//Add your NTS feature(s) to the layer. Loop through all your features and add them to the tile.
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lyr.Features.Add(myFeature);
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//Add the layer to the vector tile.
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vt.Layers.Add(lyr);
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//Output the tile to a stream.
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using (varfs=newFileStream(filePath, FileMode.Create))
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{
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//Write the tile to the stream.
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vt.Write(fs);
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}
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```
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### Read a vector tile
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The following shows how to read an individual vector tile and access the underlying NTS Features.
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```csharp
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//Create a MapboxTileReader.
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varreader=newMapboxTileReader();
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//Define which tile you want to read. You may be able to extract the x/y/zoom info from the file path of the tile.
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vartileDefinition=newNetTopologySuite.IO.VectorTiles.Tiles.Tile(x, y, zoom);
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//Open a vector tile file as a stream.
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using (varfs=newFileStream(filePath, FileMode.Open))
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{
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//Read the vector tile.
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varvt=reader.Read(fs, tileDefinition);
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//Loop through each layer.
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foreach(varlinvt.Layers)
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{
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//Access the features of the layer and do something with them.
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varfeatures=l.Features;
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}
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}
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```
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### Create tile ranges
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More often than not you want to create a collection of tiles over a bounding box area and across multiple zoom levels. The `TileRange` class makes it easy to get the ID's of all tiles within an area for a specific zoom level. You can create a tile range for each zoom level.
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```csharp
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//Create a tile range for a bounding box and specific zoom level.
//You can then enumerate over each tile within the range.
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//Enumerate using a loop. Parallel for loops can be used too, just be sure where ever you are reading your source data from can handle multiple parallel requests.
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//Smaller datasets can be stored in memory, but for larger datasets that are stored in a database, you will want to throttle the number of parallel threads.
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foreach(vartileintr)
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{
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//Read or write tiles.
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}
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//Alternatively make use the built in `EnumerateInCenterFirst` if you want to access tiles in a spiral pattern move out from the center.
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//This is useful if you are creating a dynamic rendering of the tiles.
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varcenterFirstRange=tr.EnumerateInCenterFirst();
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foreach(vartileincenterFirstRange)
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{
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//Read or write tiles.
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}
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```
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### Feature IDs
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GeoJSON features and features in vector tiles can have an ID property. This is for many things within an app, such as;
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- Using the ID of an feature to query a database and retrieve addition details that shouldn't be stored in the tiles themselves. Generally you only want the data needed for visualization in the tiles.
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- Using the ID in combination with the feature state capability in some SDKs to join external data to tiles, or create hover over effects.
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NTS features however don't have an ID property. To address this, you can pass an ID value into the attributes table of a feature. The `MapboxTileWriter` class in this library by default will automatically look at the attribute table for an attribute called `id` that is an `integer` or `ulong` number. Alternatively, when writing a tile you can specify an alternative attribute name to retrieve an ID value from. The following shows how to pass an ID from an NTS feature into it's equivalent vector tile feature when writing a vector tile.
vartileDefinition=newNetTopologySuite.IO.VectorTiles.Tiles.Tile(x, y, zoom);
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//Create a vector tile.
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varvt=newVectorTile { TileId=tileDefinition.id };
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//Create a layer.
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varlyr=newLayer { Name="layer1" };
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//Add your feature to the layer. Loop through all your features and add them to the tile.
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lyr.Features.Add(myFeature);
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//Add the layer to the vector tile.
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vt.Layers.Add(lyr);
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//Output the tile to a stream.
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using (varfs=newFileStream(filePath, FileMode.Create))
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{
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//Write the tile to the stream. This will automatically look for an "id" attribute that is a ulong or integer value as set the tile's feature ID to it.
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vt.Write(fs);
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//Alternatively, pass in a different attribute name to have the vector tiles feature use that ID value.
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//vt.Write(fs, 4096, "alternateId");
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}
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```
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Similarly, the `MapboxTileReader` class will allows you to specify an attribute name to capture the ID value in the NTS feature. If you don't specify an attribute name, the ID value won't be captured in the attribute table. This is done for backwards compatibility. The following shows how to capture a vector tile features ID and store it using a custom attribute in the attribute table.
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```csharp
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//Create a MapboxTileReader.
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varreader=newMapboxTileReader();
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//Define which tile you want to read. You may be able to extract the x/y/zoom info from the file path of the tile.
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vartileDefinition=newNetTopologySuite.IO.VectorTiles.Tiles.Tile(x, y, zoom);
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//Open a vector tile file as a stream.
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using (varfs=newFileStream(filePath, FileMode.Open))
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{
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//Read the vector tile.
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//By default ID values won't be extracted from the vector tile feature, by passing in the name of an attribute to store the ID in, the ID will be added to the attribute table.
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//You can give this any name.
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varvt=reader.Read(fs, tileDefinition, "id");
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//Loop through each layer.
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foreach(varlinvt.Layers)
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{
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//Access the features of the layer and do something with them.
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