VectorTileFeatureExtensions.cs

using System.Collections.Generic;
using System.Linq;
using GeoJSON.Net.Feature;
using GeoJSON.Net.Geometry;

namespace Mapbox.Vector.Tile
{

    public static class VectorTileFeatureExtensions
    {
        private static List<Position> Project( List<Coordinate> coords, int x, int y, int z, uint extent )
        {
            return coords.Select( coord => coord.ToPosition( x, y, z, extent ) ).ToList();
        }

        private static LineString CreateLineString( List<Position> pos )
        {
            return new LineString( pos );
        }


        private static IGeometryObject GetPointGeometry( List<Position> pointList )
        {
            IGeometryObject geom;
            if (pointList.Count == 1)
            {
                geom = new Point( pointList[0] );
            }
            else
            {
                var pnts = pointList.Select(p => new Point(p)).ToList();
                geom = new MultiPoint( pnts );
            }
            return geom;
        }

        private static List<LineString> GetLineStringList( List<List<Position>> pointList )
        {
            return pointList.Select( part => CreateLineString( part ) ).ToList();
        }

        private static IGeometryObject GetLineGeometry( List<List<Position>> pointList )
        {
            IGeometryObject geom;

            if (pointList.Count == 1)
            {
                geom = new LineString( pointList[0] );
            }
            else
            {
                geom = new MultiLineString( GetLineStringList( pointList ) );
            }
            return geom;
        }

        private static Polygon GetPolygon( List<List<Position>> lines )
        {
            var res = new List<LineString>();
            foreach (var innerring in lines)
            {
                var line = new LineString(innerring);
                if (line.IsLinearRing() && line.IsClosed())
                {
                    res.Add( line );
                }
            }
            var geom = new Polygon(res);
            return geom;
        }

        private static IGeometryObject GetPolygonGeometry( List<List<List<Position>>> polygons )
        {
            {
                IGeometryObject geom=null;

                if (polygons.Count == 1)
                {
                    geom = GetPolygon( polygons[0] );
                }
                else if (polygons.Count>0)
                {
                    var multipolys = new List<Polygon>();
                    foreach (var poly in polygons)
                    {
                        var pl = GetPolygon(poly);
                        multipolys.Add( pl );
                    }

                    geom = new MultiPolygon( multipolys );
                }
                return geom;
            }
        }

        public static List<Position> ProjectPoints( List<List<Coordinate>> Geometry, int x, int y, int z, uint extent )
        {
            var projectedCoords = new List<Position>();
            var coords = new List<Coordinate>();

            foreach (var g in Geometry)
            {
                coords.Add( g[0] );
                projectedCoords = Project( coords, x, y, z, extent );
            }
            return projectedCoords;
        }

        public static List<List<Position>> ProjectLines( List<List<Coordinate>> Geometry, int x, int y, int z, uint extent )
        {
            var projectedCoords = new List<Position>();
            var pointList = new List<List<Position>>();
            foreach (var g in Geometry)
            {
                projectedCoords = Project( g, x, y, z, extent );
                pointList.Add( projectedCoords );
            }
            return pointList;
        }

        public static List<List<List<Position>>> ProjectPolygons( List<List<List<Coordinate>>> Geometry, int x, int y, int z, uint extent )
        {
            var projectedCoords = new List<List<Position>>();
            var result = new List<List<List<Position>>>();
            foreach (var g in Geometry)
            {
                projectedCoords = ProjectLines( g, x, y, z, extent );
                result.Add( projectedCoords );
            }
            return result;
        }


        public static Feature ToGeoJSON( this VectorTileFeature vectortileFeature, int x, int y, int z )
        {
            IGeometryObject geom = null;

            switch (vectortileFeature.GeometryType)
            {
                case Tile.GeomType.Point:
                    var projectedPoints = ProjectPoints(vectortileFeature.Geometry, x, y, z, vectortileFeature.Extent);
                    geom = GetPointGeometry( projectedPoints );
                    break;
                case Tile.GeomType.LineString:
                    var projectedLines = ProjectLines(vectortileFeature.Geometry, x, y, z, vectortileFeature.Extent);
                    geom = GetLineGeometry( projectedLines );
                    break;
                case Tile.GeomType.Polygon:
                    var rings = ClassifyRings.Classify(vectortileFeature.Geometry);
                    var projectedPolygons = ProjectPolygons(rings, x, y, z, vectortileFeature.Extent);
                    geom = GetPolygonGeometry( projectedPolygons );
                    break;
            }

            var result = new Feature(geom, id: vectortileFeature.Id);

            // add attributes
            foreach (var item in vectortileFeature.Attributes)
            {
                result.Properties.Add( item.Key, item.Value );

            }
            return result;
        }
    }

}