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Hi Ian: Thanks for your test files and test code.There is no ordering implied in the vertical coordinate (or any other coordinate, except for the time coordinate in some cases), other than it must be monotonic. So user code must be able to deal with ascending or descending coordinates. So the 4.3 code is technically correct.
However, you are right that its current sort order is nonintuitive, and a change from 4.2. In fact, I didnt intend to sort it the way that you see it in the 4.3 GRIB code. The GRIB records are not ordered, so one must do a sort on these records, so one might as well sort them in some intuitive way. (Note this is diferent from netcdf, where the writer has put the coordinates in one sorted way or the another, and the CDM wont change that.)
So I would just change it so that in the future the sort order is the intuitive one, but Im not sure what happens to GRIB collections if some of the files are sorted one way, and some the other. So I have to check that out before deciding if i can easily make this change.
Thanks for reporting this! John On 7/10/2013 7:05 AM, Ian Will wrote:
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 _______________________________________________ netcdf-java mailing list netcdf-java@xxxxxxxxxxxxxxxx For list information or to unsubscribe, visit: http://www.unidata.ucar.edu/mailing_lists/
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