What is the octahedral grid ?
The octahedral grid is a form of reduced Gaussian grid with the same number of latitude lines located at the same latitude values of those of a standard Gaussian grid but with the number of longitude points at each latitude circle computed according to:
\[ {mathdisplay} N_{lat}(lat_N) = 20 \\ N_{lat}(lat_i) = N_{lat}(lat_{i+1}) + 4 \mbox{for} i=N-1,\ldots,1 {mathdisplay} \]