I've been using Netcdf Java 4.2 to read GRIB files for a number of years. I'm
excited to try 4.3. One observation when making the switch is that inverted
vertical axes (e.g. Sigma coordinate systems) seem to have switched natural z
ordering in 4.3.
Example, with a sigma coordinate system where positive is down, in 4.2 z index
29 would provide the lowest layer value. Now it appears that index 0 provides
the lowest layer value.
float sigma(sigma=30);
:units = "sigma";
:long_name = "Sigma level";
:positive = "down";
:Grib1_level_code = 107; // int
:_CoordinateAxisType = "GeoZ";
:_CoordinateZisPositive = "down";
getCoordinateValue(0) returns 10
getCoordinateValue(29) returns 31050
Similarly, an altitude about MSL layer type with positive="up" returns the
highest layer value for index 0 and the lowest for index 29.
float altitude_above_msl(altitude_above_msl=30);
:units = "m";
:long_name = "Altitude above mean sea level";
:positive = "up";
:Grib1_level_code = 103; // int
:datum = "mean sea level";
:_CoordinateAxisType = "Height";
:_CoordinateZisPositive = "up";
getCoordinateValue(0) returns 31050
getCoordinateValue(29) returns 10
I don't mind adapting to the change if its intentional, but the behavior runs
counter to my intuition regarding positive="up" or "down." Does anyone know
anything about this change?
--
Ian Will
Computer Scientist
ian.will@xxxxxxxxxxxx
will@xxxxxxxxxxxxxxxxxxxx
(202) 404-3814
