Added ap2hl docu.

OPERATORS

@@ -470,7 +470,8 @@ Operator catalog:
    Remapeta      remapeta        Remap vertical hybrid level
    Vertint       ml2pl           Model to pressure level interpolation
    Vertint       ml2hl           Model to height level interpolation
-   Vertintap     ap2pl           Model to pressure level interpolation
+   Vertintap     ap2pl           Air pressure to pressure level interpolation
+   Vertintap     ap2hl           Air pressure to height level interpolation
    Intlevel      intlevel        Linear level interpolation
    Intlevel3d    intlevel3d      Linear level interpolation onto a 3d vertical coordinate
    Intlevel3d    intlevelx3d     like intlevel3d but with extrapolation

doc/tex/mod/Vertintap

@@ -4,29 +4,55 @@
 @Section   = Interpolation
 @Class     = Interpolation
 @Arguments = ifile ofile
-@Operators = ap2pl
+@Operators = ap2pl ap2hl
 
 @BeginDescription
-Interpolate 3D variables on hybrid sigma height coordinates to pressure levels.
+Interpolate 3D variables on hybrid sigma height coordinates to pressure or height levels.
 The input file must contain the 3D air pressure. The air pressure is identified
 by the NetCDF CF standard name air_pressure.
-This operator requires all variables on the same horizontal grid.
+Use the alias  @bold{ap2plx}/@bold{ap2hlx} or the environment variable @env{EXTRAPOLATE}
+to extrapolate missing values. This operator requires all variables on the same horizontal grid.
 @EndDescription
 @EndModule
 
 
 @BeginOperator_ap2pl
-@Title     = Model to pressure level interpolation
+@Title     = Air pressure to pressure level interpolation
 @Parameter = plevels
+
+@BeginDescription
+Interpolates 3D variables on hybrid sigma height coordinates to pressure level.
+@EndDescription
+@EndOperator
+
+
+@BeginOperator_ap2hl
+@Title     = Air pressure to height level interpolation
+@Parameter = hlevels
+
+@BeginDescription
+Interpolates 3D variables on hybrid sigma height coordinates to height level.
+The procedure is the same as for the operator @oper{ap2pl} except for
+the pressure levels being calculated from the heights by:
+@math{plevel = 101325*exp(hlevel/-7000)}
+@EndDescription
 @EndOperator
 
 
 @BeginParameter
 @Item = plevels
 FLOAT  Pressure levels in pascal
+@Item = hlevels
+FLOAT  Height levels in meter (max level: 65535 m)
 @EndParameter
 
 
+@BeginEnvironment
+@Item = EXTRAPOLATE
+If set to 1 extrapolate missing values.
+@EndEnvironment
+
+
 @BeginNote
 This is a specific implementation for NetCDF files from the ICON model, it may not work with data from other sources.
 @EndNote

src/operator_help.h

@@ -3908,19 +3908,35 @@ static const char *VertintmlHelp[] = {
 
 static const char *VertintapHelp[] = {
     "NAME",
-    "    ap2pl - Vertical interpolation",
+    "    ap2pl, ap2hl - Vertical interpolation",
     "",
     "SYNOPSIS",
     "    ap2pl,plevels  ifile ofile",
+    "    ap2hl,hlevels  ifile ofile",
     "",
     "DESCRIPTION",
-    "    Interpolate 3D variables on hybrid sigma height coordinates to pressure levels.",
+    "    Interpolate 3D variables on hybrid sigma height coordinates to pressure or height levels.",
     "    The input file must contain the 3D air pressure. The air pressure is identified",
     "    by the NetCDF CF standard name air_pressure.",
-    "    This operator requires all variables on the same horizontal grid.",
+    "    Use the alias  ap2plx/ap2hlx or the environment variable EXTRAPOLATE",
+    "    to extrapolate missing values. This operator requires all variables on the same horizontal grid.",
+    "",
+    "OPERATORS",
+    "    ap2pl  Air pressure to pressure level interpolation",
+    "           Interpolates 3D variables on hybrid sigma height coordinates to pressure level.",
+    "    ap2hl  Air pressure to height level interpolation",
+    "           Interpolates 3D variables on hybrid sigma height coordinates to height level.",
+    "           The procedure is the same as for the operator ap2pl except for",
+    "           the pressure levels being calculated from the heights by:",
+    "           plevel = 101325*exp(hlevel/-7000)",
     "",
     "PARAMETER",
     "    plevels  FLOAT  Pressure levels in pascal",
+    "    hlevels  FLOAT  Height levels in meter (max level: 65535 m)",
+    "",
+    "ENVIRONMENT",
+    "    EXTRAPOLATE",
+    "        If set to 1 extrapolate missing values.",
     "",
     "NOTE",
     "    This is a specific implementation for NetCDF files from the ICON model, it may not work with data from other sources.",