Docu update

doc/tex/grid.tex

@@ -34,7 +34,6 @@ set or overwrite the grid cell area.
 \label{GRID_DESCRIPTION}
 
 In the following situations it is necessary to give a description of a horizontal grid:
-
 \begin{itemize}
 \item Changing the grid description (operator: \htmlref{setgrid}{setgrid})
 \item Horizontal interpolation (all remapping operators)
@@ -45,7 +44,7 @@ As now described, there are several possibilities to define a horizontal grid.
 
 \subsubsection{Predefined grids}
 
-Predefined grids are available for global regular, gaussian or icosahedral-hexagonal GME grids.
+Predefined grids are available for global regular, gaussian, HEALPix or icosahedral-hexagonal GME grids.
 % They have the following predefined grid names: 
 %\texttt{r<NX>x<NY>}, \texttt{lon=<LON>/lat=<LAT>}, \texttt{n<N>} and \texttt{gme<NI>}
 
@@ -94,6 +93,14 @@ Predefined grids are available for global regular, gaussian or icosahedral-hexag
     \texttt{gme<NI>} defines a global icosahedral-hexagonal GME grid.
     \texttt{NI} specifies the number of intervals on a main triangle side.
 
+\subsubsection*{HEALPix grid: \texttt{hp<NSIDE>[b][\_<ORDER>]}}
+    HEALPix is an acronym for Hierarchical Equal Area isoLatitude Pixelization of a sphere.
+    \texttt{hp<NSIDE>[b][\_<ORDER>]} defines a global HEALPix grid.
+    The resolution is defined by the NSIDE parameter, which is generally a power of 2.
+    NSIZE=1 generates the HEALPix base partitioning of the sphere surface into 12 (H=4, K=3) equal sized pixels.
+    \texttt{ORDER} describes the ordering of the pixels. Available are nest (default) or ring ordering.
+    If the parameter \texttt{b}  is set, the grid cell corners are also calculated.
+
 \subsubsection{Grids from data files}
 
 You can use the grid description from an other datafile.