gis矢量切片算法

对于大范围矢量数据，由于类型众多范围广泛往往数据量极大，加载渲染会造成平台卡顿。因此对矢量数据进行四叉树索引切片可以高效加载当前区域矢量，提高效率。

常见的矢量数据为shapefile，可以通过GDAL读取shp范围进行四叉树划分，构建某一层级瓦块。

以下为C#调用GDAL进行矢量四叉树切片算法：

 struct TileStructure    {        public int level;        public int x;        public int y;        public OSGeo.OGR.Geometry extentPolygon;        public string path;        public OSGeo.OGR.DataSource ds;        public OSGeo.OGR.Layer layer;         }    public class VectorTileTool    {        List<TileStructure> tiles;        public VectorTileTool()        {        }        public bool SeprateShpLayer(string sourcePath, string resultFolder, int level)        {            OSGeo.GDAL.Gdal.SetConfigOption("SHAPE_ENCODING", "");            OSGeo.OGR.Ogr.RegisterAll();            OSGeo.OGR.Driver dr = OSGeo.OGR.Ogr.GetDriverByName("ESRI shapefile");            if (dr == null)            {                return false;            }            OSGeo.OGR.DataSource ds = dr.Open(sourcePath, 0);            int layerCount = ds.GetLayerCount();            OSGeo.OGR.Layer layer = ds.GetLayerByIndex(0);            //投影信息            OSGeo.OSR.SpatialReference coord = layer.GetSpatialRef();            string coordString;            coord.ExportToWkt(out coordString);            //地理范围            Envelope layerEx = new Envelope();            layer.GetExtent(layerEx, 0);            ////如果瓦块数据存在，全部删除            //if (Directory.Exists(resultFolder))            //{            //    Directory.Delete(resultFolder,true);            //}            //创建文件夹            Directory.CreateDirectory(resultFolder + "\\JSON\\");            //针对本项目，划分第16级，根据地理范围求出瓦片            int y0 = Convert.ToInt32((90 - layerEx.MaxY) * Math.Pow(2, level)/180.0);            int x0 = Convert.ToInt32((180 + layerEx.MinX) * Math.Pow(2, level)/180.0);            int y1 = Convert.ToInt32((90 - layerEx.MinY) * Math.Pow(2, level) / 180.0);            int x1 = Convert.ToInt32((180 + layerEx.MaxX) * Math.Pow(2, level) / 180.0);            //20160621 ZXQ 创建层行列配置文件            string filePath = resultFolder + "\\JSON\\" + "\\tile.txt";            FileStream fs = new FileStream(filePath, FileMode.CreateNew);            StreamWriter sw = new StreamWriter(fs);            //写入层行列            sw.Write(level.ToString());            sw.Write(",");            sw.Write(x0.ToString());            sw.Write(",");            sw.Write(x1.ToString());            sw.Write(",");            sw.Write(y0.ToString());            sw.Write(",");            sw.Write(y1.ToString());            sw.Write(",");            sw.Write("json");            sw.Flush();            sw.Close();            fs.Close();            tiles = new List<TileStructure>();            for (int x =x0;x<=x1;x++)            {                for (int y=y0;y<=y1;y++)                {                    TileStructure tile;                    tile.level = level;                    tile.x = x;                    tile.y = y;                    double lonMin = -180 + 180 / (Math.Pow(2, level)) * x;                    double lonMax = -180 + 180 / (Math.Pow(2, level)) * (x + 1);                    double latMax = 90 - 180 / (Math.Pow(2, level)) * y;                    double latMin = 90 - 180 / (Math.Pow(2, level)) * (y + 1);                    tile.extentPolygon = new OSGeo.OGR.Geometry(OSGeo.OGR.wkbGeometryType.wkbPolygon);                    OSGeo.OGR.Geometry geo = new OSGeo.OGR.Geometry(OSGeo.OGR.wkbGeometryType.wkbLinearRing);                    geo.AddPoint(lonMin,latMax,0);                    geo.AddPoint(lonMax, latMax, 0);                    geo.AddPoint(lonMin, latMin, 0);                    geo.AddPoint(lonMax, latMin, 0);                    tile.extentPolygon.AddGeometryDirectly(geo);                    tile.extentPolygon.CloseRings();                    //创建空shp文件                    string tileFolder = resultFolder + "\\SHP\\" + level.ToString() + "\\" + x.ToString();                    string fileName = y.ToString() + ".shp";                    string tilePath = tileFolder + "\\" + fileName;                    if (!Directory.Exists(tileFolder))                    {                        Directory.CreateDirectory(tileFolder);                    }                    tile.path = tilePath;                                        tile.ds = dr.CreateDataSource(tilePath, null);                    tile.layer = tile.ds.CreateLayer("house", coord, OSGeo.OGR.wkbGeometryType.wkbPolygon, null);                    FieldDefn fd = new FieldDefn("HEIGHT", FieldType.OFTReal);                    tile.layer.CreateField(fd,1);                    tiles.Add(tile);                    Console.WriteLine("创建第{0}层第{1}行第{2}列瓦块空shapefile数据", level, x, y);                }            }            OSGeo.OGR.Feature feat;            //读取shp文件            while ((feat = layer.GetNextFeature()) != null)            {                int id = feat.GetFID();                OSGeo.OGR.Geometry geometry = feat.GetGeometryRef();                OSGeo.OGR.wkbGeometryType goetype = geometry.GetGeometryType();                if (goetype != wkbGeometryType.wkbPolygon)                {                    continue;                }                geometry.CloseRings();                //随机楼层3-15层                Random random = new Random();                double height = random.Next(3,15)*3;// feat.GetFieldAsDouble("房屋层数") * 3;                for (int i = 0; i < tiles.Count;i++ )                {                    TileStructure tile = tiles[i];                    //如果瓦片与要素相交，则将要素放入该瓦片                    if (tile.extentPolygon.Intersect(geometry))                    {                        OSGeo.OGR.Feature poFeature = new Feature(tile.layer.GetLayerDefn());                                             poFeature.SetField(0, height.ToString());                        poFeature.SetGeometry(geometry);                        tile.layer.CreateFeature(poFeature);                        Console.WriteLine("写入第{0}个要素入shp", id);                    }                }            }            return true;        }}