c#gdal解析气象数据生成等值线openlayers展示

当前场景：
1. 下载的全球气象数据存储在txt文件中
2. 解析数据生成等值线txt文件，存储在mongodb中
3. 加载数据传给前端，openlayers渲染等值线

技术探讨思路：
1. 根据世界坐标系生成世界坐标点180*361
2. c#读取txt文件气压值或者其他等值线权重值，与上面坐标一一对应，x,y,m格式输出存储到新的txt文件中，每行一条数据
3. 调用gdal加载2中文件，调用gdal方法，设置对应参数，生成等值线bln文件
4. 解析bln等值线数据，提取等值线，根据自己需要的格式存储到txt文件中
5. 前端加载文件，解析成geojson数据展示

• 生成坐标系

  /// <summary>
  
      /// 返回网格坐标
  
      /// </summary>
  
      /// <returns></returns>
  
      public List<COORD> BuildCoord() {
  
          List<COORD> lst = new List<COORD>();
  
          for (int i = 90; i>=-90; i--) {
  
              for (int m = 0; m < 180; m++) {
  
                  COORD coord = new COORD();
  
                  coord.x = m;
  
                  coord.y = i;
  
                  lst.Add(coord);
  
              }
  
              for (int m = -180; m < 0; m++)
  
              {
  
                  COORD coord = new COORD();
  
                  coord.x = m;
  
                  coord.y = i;
  
                  lst.Add(coord);
  
              }
  
          }
  
          return lst;
  
      }

• 读取解析气象数据生成x,y,m文件
  ` ////// 读取文件中地面压力数据
  ///

  ///public List fileToString(String filePath)
  {
  filePath = System.Web.HttpContext.Current.Server.MapPath("~") + filePath;
  string strData = "";
  List outData = new List();
  try
  {
  //获取坐标点
  List c =BuildCoord();
  string line;
  // 创建一个 StreamReader 的实例来读取文件 ,using 语句也能关闭 StreamReader
  using (StreamReader sr = new StreamReader(filePath))
  {
  string lineData = sr.ReadLine();
  int count = 1;
  // 从文件读取并显示行，直到文件的末尾
  while ((line = sr.ReadLine()) != null)
  {
  strData = line.Trim();
  if (count ==5) {
  string l = line;
  var data = line.Split(' ');
  for (int i = 0; i < data.Length; i++) {
  XYZ d = new XYZ();
  d.x = c[i].x;
  d.y = c[i].y;
  d.m = double.Parse(data[i]);
  outData.Add(d);
  if (i == c.Count-1)
  {
  line = null;
  break;
  }
  }
  }
  count++;
  }

              sr.Close();
              sr.Dispose();
          }
  
      }
      catch (Exception e)
      {
          // 向用户显示出错消息
          Console.WriteLine("The file could not be read:");
          Console.WriteLine(e.Message);
      }
      return outData;
  }`
  

• 调用gdal生成等值线，以geojson格式存储等值线数据
  `// 传入的文件格式如下
  // X Y Z
  // 112.536542357878 21.4983645627334 299.1500
  // 112.536542357878 21.5067224997793 299.1500
  // 112.536542357878 21.5150799564311 299.1502
  // 112.536542357878 21.5234369325389 299.1498
  // 112.536542357878 21.5317934279523 299.1501
  // 112.536542357878 21.5401494425214 299.1502
  // 文件第一行无实际作用,其余为点数据,一个点占一行

  public  string Create(string path, int rowCnt, int colCnt, double[] array = null)
  {
      string filename = Path.GetFileNameWithoutExtension(path);
      string filepath = Path.GetDirectoryName(path)+"\\";
      DateTime time1 = DateTime.Now;
      ///如果为true则将结果保存至数据库,便于通过geoserver查看结果
      ///如果为false则将结果保存至文件,并在数据库中插入一条记录
      string lineText = filepath+filename + ".txt";
      string grdfile = Guid.NewGuid().ToString() + ".grd";
      string blnfile = grdfile.Replace("grd", "bln");
      try
      {
          Surfer.Application app = new Surfer.Application();
          app.GridData2(DataFile: path,                   //数据文件地址
              xCol: 1,                                        //x为第一列数据
              yCol: 2,                                        //y为第二列数据
              zCol: 3,                                        //z为第三列数据
              DupMethod: Surfer.SrfDupMethod.srfDupAvg,
              //xMin: 112.536542357878,                       //x最小值
              //xMax: 113.434857642122,                       //x最大者
              //yMin: 21.4983645627334,                       //y最小值
              //yMax: 22.3317562252913,                       //y最大值
              Algorithm: Surfer.SrfGridAlgorithm.srfKriging,  //插值算法Kriging
              NumCols: rowCnt,                                //x方向插值数据量
              NumRows: colCnt,                                //y方向插值数据量
              OutGrid: filepath + grdfile,                        //返回文件为gridfile
              OutFmt: Surfer.SrfGridFormat.srfGridFmtAscii);  //返回文件编码为Ascii
  
          Surfer.IDocuments docs = app.Documents;
          Surfer.IPlotDocument Doc = (Surfer.IPlotDocument)docs.Add(Surfer.SrfDocTypes.srfDocPlot);//创建一个空白绘图文档
          Surfer.IShapes Shapes = Doc.Shapes;
  
          Surfer.IMapFrame contourMapFrame = Shapes.AddContourMap(filepath+ grdfile);//加载网格文件，这个是上面生成的grd文件
  
          Surfer.IContourMap contourMap = (Surfer.IContourMap)contourMapFrame.Overlays.Item(1);
          contourMap.SmoothContours = Surfer.SrfConSmoothType.srfConSmoothHigh;//平滑等值线边界当前设置不平滑
          if (array != null) contourMap.Levels.AutoGenerate(array[0], array[1], array[2]);//设置等值线间隔
          //string strWH = string.Format("width={0:f0},height={1:f0},KeepAspect=1,ColorDepth=32",540,420);//设置输出图片的高度和宽度
          //Doc.Export(@"C:\1.png", SelectionOnly: false, Options: strWH);//设置输出图片格式名
          Doc.Export(filepath + blnfile);//生成等值线文件
          Doc.Close(Surfer.SrfSaveTypes.srfSaveChangesNo);//不生成srf文件
          app.Quit();//退出
          System.GC.Collect(System.GC.GetGeneration(app));//释放
          File.Delete(filepath + grdfile);
          TimeSpan ts = DateTime.Now - time1;
  
          //导出geojson数据
  
          //  以下为读取入库,文件格式如下
          //  8,0 "299.1496"
          //  112.577002425616,22.33175623,0
          //  112.572474916,22.3275559359832,0
          //  112.563491762,22.3275559359832,0
          //  112.559036117616,22.3234223133,0
          //  112.554508608,22.3192220192832,0
          //  112.549981098384,22.3234223133,0
          //  112.545525454,22.3275559359832,0
          //  112.5365423,22.3275559359832,0
          //  第一行为：点个数，未知，高程值
          //  余下的行为点数据，一个点占一行
  
          if (!File.Exists(filepath + blnfile)) return "";
  
          FileStream fs = new FileStream(filepath + blnfile, FileMode.Open, FileAccess.ReadWrite);
          StreamReader sr = new StreamReader(fs, UnicodeEncoding.UTF8);
  
          Dictionary<string, double> dicZ = new Dictionary<string, double>();
          Dictionary<string, List<string>> dicLine = new Dictionary<string, List<string>>();
  
          double z = 0.0;
          int cnt = 0;
          int index = 0;
          string guid = "";
          string line = string.Empty;
  
          while ((line = sr.ReadLine()) != null)
          {
              if (line != null && line != "")
              {
                  if (line.IndexOf("\"") > -1)
                  {
                      index = 0;
                      string[] str = line.Split(' ');
                      cnt = Convert.ToInt32(str[0].Split(',')[0]);
                      z = Convert.ToDouble(str[1].Replace("\"", ""));
                      guid = Guid.NewGuid().ToString();
  
                      dicZ.Add(guid, z);
  
                      continue;
                  }
  
                  index++;
                  if (index <= cnt)
                  {
                      if (!dicLine.ContainsKey(guid))
                          dicLine.Add(guid, new List<string>());
  
                      dicLine[guid].Add(line);
                  }
              }
          }
          sr.Close();
          fs.Close();
          sr.Dispose();
          fs.Dispose();
  
          //string sql1 = "INSERT INTO contour_3d(guidid, taskid, type, height, ordernum, value, lineobj) VALUES('{0}','{1}','{2}',{3},{4},{5},{6})";
          //文件覆盖方式添加内容
          System.IO.StreamWriter file = new System.IO.StreamWriter(lineText, false);
          foreach (var v in dicLine)
          {
              //string lineGeoJson = "{ \"type\": \"LineString\", \"coordinates\": [ [100.0, 0.0], [101.0, 1.0] ],\"properties\":{\"m\":2} }";
              string lineobj = "{\"type\": \"Feature\",\"geometry\": { \"type\": \"LineString\", \"coordinates\": [";
              foreach (var p in v.Value)
              {
                  lineobj += string.Format("[{0},{1}],", p.Split(',')[0], p.Split(',')[1]);
              }
              lineobj = lineobj.Substring(0, lineobj.Length - 1);
              lineobj += "]},\"properties\":{\"m\":" + dicZ[v.Key] + "}}\r\n";
              file.Write(lineobj);
              //string str = string.Format(sql1, v.Key, taskid, type, high, order, dicZ[v.Key], lineobj);
              //DbHelperPostSQL.ExecuteSql(str);
  
          }
          file.Flush();
          //关闭文件
          file.Close();
          //释放对象
          file.Dispose();
          File.Delete(filepath + blnfile);
          return lineText;
      }
      catch (Exception ex)
      {
          //string msg = string.Format("{0}\t高度{1}\t顺序{2}\r\n", ex.Message, high, order);
          //File.AppendAllText(filename + "\\wholeText.txt", msg, System.Text.ASCIIEncoding.UTF8);
          return "";
      }
  
  }
  

  `

• openlayers加载geojson数据添加到地图上

  var contourL = new ol.layer.Vector({
      source: new ol.source.Vector(),
      style: function (f, r) {
          var txt = f.getProperties().m;
          return new ol.style.Style({
              stroke: new ol.style.Stroke({
                  color: '#00EEFF',
                  width: 2
              }),
              text: new ol.style.Text({
                  text: txt.toString()
              })
          })
      }
  });
  $.ajax({
      url: './Controller/Main.ashx?type=showcontour&path=' + p,
      type: 'get',
      dataType: 'json',
      success: function (data) {
          var gj = new ol.format.GeoJSON();
          var geoJsons = data;
          var ex = ol.extent.createEmpty();
          var fs = [];
          geoJsons.forEach(function (item) {
              var f = gj.readFeature(item);
              ex = ol.extent.containsExtent(f.getGeometry().getExtent(), ex);
              fs.push(f);
          })
          contourL.getSource().clear();
          contourL.getSource().addFeatures(fs);
          map.getView().fit(ex, map.getSize());
      },
      error: function (e) {
          console.log(e);
      }
  })

注：代码可联系下载，提供技术支持