Problems and questions using vtkSmartVolumeMapper for large volume streaming and rendering

Sorry, my question is about how to compile VTK with OSPRay,

I have already checked Module_vtkRenderingOSPRay in cmake-gui and recompile VTK, but my program got error as:

Warning VTK is not linked to OSPRay so can not VolumeRender with it

What did I miss?

The error is fixed after I add below two lines:

vtkOSPRayPass* osprayPass = vtkOSPRayPass::New();
render->SetPass(vtkOSPRayPass);

thanks!