IPoilygon转IPoint

 private void 河流面转点ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            ESRI.ArcGIS.Geodatabase.IWorkspaceFactory wsf = new ESRI.ArcGIS.DataSourcesFile.ShapefileWorkspaceFactory();
            IWorkspace ws = wsf.OpenFromFile(@"F:1-水利项目安徽水利826处理", 0);

            IFeatureClass autoStation = (ws as IFeatureWorkspace).OpenFeatureClass("淮河干流面");
            IFeatureClass f1 = (ws as IFeatureWorkspace).OpenFeatureClass("河道范围点");

            int num = autoStation.FeatureCount(null);            
            int k = 0;
            string file = @"F:1-水利项目安徽水利ANSL20120808ANSLOutPut淮河干流hedaopolygon.txt";
            if (File.Exists(file))
            {
                File.Delete(file);
            }
            StreamWriter writer = new StreamWriter(file, true);
            string strpt = "";
            for (int i = 0; i < num; i++) 
            {
                IPolygon pg = autoStation.GetFeature(i).Shape as IPolygon;
                                  
                IPointCollection ptc = pg as IPointCollection;
                for (int j = 0; j < ptc.PointCount; j++)
                {
                    IPoint pt = ptc.get_Point(j);
                    k++;
                    IFeature fea = f1.CreateFeature();
                    fea.Shape = pt;
                    fea.set_Value(fea.Fields.FindField("Id"), k);
                    fea.set_Value(fea.Fields.FindField("longi"), pt.X);
                    fea.set_Value(fea.Fields.FindField("latit"), pt.Y);
                    fea.Store();

                    strpt=strpt+pt.X+","+pt.Y+","+"0,";
                }
                strpt = strpt + ptc.get_Point(0).X + "，" + ptc.get_Point(0).Y + "," + "0,";        
            }
            writer.Write(strpt);
            writer.Close();
        }

IPolygon转换为IPoint，且点的坐标值写入txt中。