Engine做通视分析时如何选择部分DEM而不是全部？

 

            string folderName = @E:\test;

            IWorkspaceFactory workspaceFactory = new RasterWorkspaceFactoryClass();

            IWorkspace wksp = workspaceFactory.OpenFromFile(folderName,0);

            IRasterWorkspace rasterWorkspace = (IRasterWorkspace)workspaceFactory.OpenFromFile(folderName, 0);

            IRasterDataset dem = rasterWorkspace.OpenRasterDataset(elevation1.tif);

            IGeoDataset indem = dem as IGeoDataset;

            ISpatialReference sparef = indem.SpatialReference;



            IEnvelope env = new EnvelopeClass();

            env.XMin = 483014;

            env.XMax = 491696;

            env.YMin = 224307;

            env.YMax = 229781;

            env.SpatialReference = sparef;



            IExtractionOp exop = new RasterExtractionOpClass();

            IGeoDataset output = exop.Rectangle(indem, env, true);



            IWorkspaceFactory shpwks = new ESRI.ArcGIS.DataSourcesFile.ShapefileWorkspaceFactoryClass();

            IFeatureWorkspace featureworksps = (IFeatureWorkspace)shpwks.OpenFromFile(folderName, 0);

            IFeatureClass featureClass = featureworksps.OpenFeatureClass(pts);

            IGeoDataset pts = featureClass as IGeoDataset;



            ISurfaceOp surop = new RasterSurfaceOpClass();

            IGeoDataset visiout = surop.Visibility(output, pts, esriGeoAnalysisVisibilityEnum.esriGeoAnalysisVisibilityFrequency);



            IRaster raster = visiout as IRaster;

            IRasterLayer ralayer = new RasterLayerClass();

            ralayer.CreateFromRaster(raster);

            axMapControl1.AddLayer(ralayer);