Add surface calculation if HGTS is requested from gfsfile.

radixio/gfsfile.cc

@@ -799,6 +799,14 @@ std::vector<std::vector<float>> GFSFile::query(float lat, float lon, int month,
     // initialize space for results vector
     results[ll] = std::vector<float>(columns.size(), 0.0f);
 
+    // if "HGTS" has been requested add level as the default HGTS
+    auto hIt = std::find(columns.begin(), columns.end(), "HGTS");
+    if (hIt != columns.end())
+    {
+      results[ll][hIt - columns.begin()] =
+          hypsometric(msle, plevel, temp) - surfaceAltitude;
+    }
+
     // check for time
     auto timeIt = std::find(columns.begin(), columns.end(), "TIME");
     if (timeIt != columns.end())