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:

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N_{lat}(lat_N) = 20 \\
N_{lat}(lat_i) = N_{lat}(lat_{i+1}) + 4 \mbox{for} i=N-1,\ldots,1
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