double ossimTiledElevationDatabase::getHeightAboveEllipsoid(const ossimGpt& gpt)
{
   double h = getHeightAboveMSL(gpt);
   if(h != ossim::nan())
   {
      h += getOffsetFromEllipsoid(gpt);
   }
   return h;
}
double ossimImageElevationDatabase::getHeightAboveEllipsoid(const ossimGpt& gpt)
{
   double h = getHeightAboveMSL(gpt);
   if(!ossim::isnan(h))
   {
      h += getOffsetFromEllipsoid(gpt);
   }
   return h;
}