GIS矢量切片算法

转自： https://www.giserdqy.com/database/postgresql/25838/

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 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();  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; }}

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GIS矢量切片算法（转载）
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