GlobeControl中如何根据视角（视线）求三维点和dem表面的交点？

private void get_intersection(string path, string filename, IPoint pt) 

{ 

//Open a file raster dataset. 

IWorkspaceFactory workspaceFactory = new RasterWorkspaceFactoryClass(); 

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

IRasterDataset rasterDataset = rasterWorkspace.OpenRasterDataset(filename); 

IRasterBandCollection rasterbands = (IRasterBandCollection)rasterDataset; 

IRasterBand rasterband = rasterbands.Item(0); 

IRasterSurface rastersurface = new RasterSurfaceClass(); 

rastersurface.RasterBand = rasterband; 

ISurface surface = new RasterSurfaceClass(); 

surface = rastersurface as ISurface; 



//construct sight line ray 

IVector3D vector = new Vector3DClass(); 

vector.XComponent = 0.2; 

vector.YComponent = 0; 

vector.ZComponent = -1; 



//construct vertical ray 

//IVector3D vector = new Vector3DClass(); 

//vector.XComponent = 0; 

//vector.YComponent = 0; 

//vector.ZComponent = -1; 



IRay ray = new RayClass(); 

ray.Vector = vector; 

ray.Origin = pt; 



//get intersection point 

IPoint inter = new PointClass(); 

inter = surface.Locate(ray, 1); 



double elevation; double z; 

elevation = surface.GetElevation(inter); 

z = surface.get_Z(inter.X, inter.Y);