[netcdf-java] Inverted vertical axis change in 4.3?

• To: "netcdf-java@xxxxxxxxxxxxxxxx" <netcdf-java@xxxxxxxxxxxxxxxx>
• Subject: [netcdf-java] Inverted vertical axis change in 4.3?
• From: Ian Will <ian.will@xxxxxxxxxxxx>
• Date: Wed, 10 Jul 2013 13:05:13 +0000

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

• Follow-Ups:
  • Re: [netcdf-java] Inverted vertical axis change in 4.3?
    • From: John Caron
  • Re: [netcdf-java] Inverted vertical axis change in 4.3?
    • From: John Caron