Docu update.

doc/tex/grid.tex

@@ -94,11 +94,12 @@ Predefined grids are available for global regular, gaussian, HEALPix or icosahed
     \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.
+    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.
+    The \texttt{NSIDE} parameter controls the resolution of the pixellization. 
+    It is the number of pixels on the side of each of the 12 top-level HEALPix pixels.
+    \texttt{NSIDE=1} generates the 12 (H=4, K=3) equal sized top-level HEALPix pixels.
+    \texttt{ORDER} sets the index ordering convention of the pixels, available are \texttt{ring} (default) or \texttt{nest} ordering.
     If the parameter \texttt{b}  is set, the grid cell corners are also calculated.
 
 \subsubsection{Grids from data files}