Description of the format of grids from the RAF family
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Header:
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6 numeric values, 2 by row:
   42.0000000000000     51.5000000000000
   -5.50000000000000     8.50000000000000
    0.0250000000000000   0.0333333333333333

corresponding to:
latitude_limit_south         latitude_limit_north
longitude_limit_west         longitude_limit_east
step_in_latitude             step_in_longitude

Values are in decimal degrees.

Grid description:
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by latitude from north to south
for each latitude, by longitude from west to east.

Physically: for each latitude, 52 rows of 8 values, 1 row of 5 values.
Logically: grid of 381 rows (latitudes) by 421 columns (longitude).

Values (height of the altitude reference surface above the ellipsoid) are in meters.