国家大地2000坐标系的椭球坐标系（4490）与平面坐标系（投影坐标系）4547，4548，4549...的面积对比

IWorkspaceFactory pWSF = new FileGDBWorkspaceFactoryClass();
            IFeatureWorkspace pFWS = (IFeatureWorkspace)pWSF.OpenFromFile(@"D:\gis数据\测试0303.gdb", 0);
            IFeatureClass Featureclass = pFWS.OpenFeatureClass("CS");
            IFeatureClass Featureclass2 = pFWS.OpenFeatureClass("CS_4547");
            IFeatureClass Featureclass3 = pFWS.OpenFeatureClass("CS_4548");
            IFeatureClass Featureclass4 = pFWS.OpenFeatureClass("CS_4549");
            var fcur = Featureclass.Search(null, false);
            var fcur2 = Featureclass2.Search(null, false);
            var fcur3 = Featureclass3.Search(null, false);
            var fcur4 = Featureclass4.Search(null, false);
            IFeature pFeature = fcur.NextFeature();
            IFeature pFeature2 = fcur2.NextFeature();
            IFeature pFeature3 = fcur3.NextFeature();
            IFeature pFeature4 = fcur4.NextFeature();
            IPolygon polygon = pFeature.ShapeCopy as IPolygon;
            IPolygon polygon2 = pFeature2.ShapeCopy as IPolygon;
            IPolygon polygon3 = pFeature3.ShapeCopy as IPolygon;
            IPolygon polygon4 = pFeature4.ShapeCopy as IPolygon;
            
            IArea pArea = polygon as IArea;
            IArea pArea2 = polygon2 as IArea;
            IArea pArea3 = polygon3 as IArea;
            IArea pArea4 = polygon4 as IArea;
            double area = Math.Abs(pArea.Area);
            double area2 = Math.Abs(pArea2.Area);
            double area3 = Math.Abs(pArea3.Area);
            double area4 = Math.Abs(pArea4.Area);

            //4490
            IAreaGeodetic areaGeodetic = polygon as IAreaGeodetic;
            ISpatialReferenceFactory srf = new SpatialReferenceEnvironmentClass();
            ILinearUnit unit = srf.CreateUnit((int)esriSRUnitType.esriSRUnit_Meter) as ILinearUnit;
            double area11 = areaGeodetic.get_AreaGeodetic(esriGeodeticType.esriGeodeticTypeGeodesic, unit);

            //zhaun4547转4490
            //IGeometry geo22 = (IGeometry)po

同一个图形作转换与对比：

//总结：4547,4548转换成4490，然后计算其面积跟4490的是相差不多的
//4547转4548或者是转4549，跟没有转换的4548，4549的也是相差不多的
//如果没有转换的话，相同的图斑4490与4547,4548，4549...的面积是依次相差越来越大的