[ORD CE c++]How to get data from DTM?

I am trying to get data from a terrain model. now i have got DTM object:

auto ts = TerrainSurface::CreateFromElementHandle(eeh);
if (!ts.IsValid())
{
mdlDialog_dmsgsPrint(L"not a terrain surface");
return;
}
DTMPtr dtm = ts->GetDTM();
if (!dtm.IsValid())
{
mdlDialog_dmsgsPrint(L"invalid dtm");
return;
}

eeh is the ElementHandle of the terrain model object. Could anyone tell me how to deal with the DTM object?