c#AE求助，怎么实现读取某个路径下的DEM数据，并提取其坡度坡长（菜鸟日常，求助大神）

问题是这样的，我把一个DEM数据放在了一个文件夹里面，然后读取他，对他进行坡度提取和坡长提取，自己从网上找了方法，行不通，有没有大神可以帮帮我。
private object missing = Type.Missing;
private IDataset pGeoDataset;
private ISurfaceOp surfaceOp;
private IGeoDataset OutDS;

                                esriGeoAnalysisSlopeEnum slopeEnum;
                slopeEnum = esriGeoAnalysisSlopeEnum.esriGeoAnalysisSlopeDegrees;


                IImageServerLayer imageserverlayer = new ImageServerLayerClass();
                string URL = @"..\..\SampleData\dem";
                imageserverlayer.Initialize(URL);
                IRaster raster = imageserverlayer.Raster;
                IGeoDataset pInDs = raster as IGeoDataset;

                 surfaceOp = new RasterSurfaceOpClass();
                 OutDS = surfaceOp.Slope(pInDs, slopeEnum, ref missing);

真心求助了，大神们能帮帮忙吗