NOAA / NWS's Meteorological Development Laboratory
Degrib (NDFD GRIB2 Decoder) 
|
NOAA / NWS's Meteorological Development Laboratory
| |
|
|
Degrib (NDFD GRIB2 Decoder) |
 |
NDFD Home | Verification | News | Organization |  |
|
Subject: Degrib version 1.18
Date: Fri, 06 Jun 2003 18:59:55 -0400 From: "Arthur.Taylor" Organization: DOC/NOAA/NWS - National Weather Service To: Arthur Taylor Hi You all have the unique distinction of being registered on my degrib (aka NDFD_GRIB2Decoder) mailing list (all 63 of us) (I'd like to welcome: mmuttray and apiradee_s059) Please let me know (email me) if you want to unregister. First, some news... 1) As some of you may have noticed, Temp and Dew Point for the CONUS started appearing on somewhere around 6/3/2003. I think it was officially announced that there would be Temp and Dew Point starting today. (Note: the http option in version 1.17 timed out on the CONUS Temp and Dew Point files, I have now fixed that). 2) On June 16, files are also expected to be available with forecasts for PoP12, Weather, Sky Cover, QPF, Snow Amount, Wave Height, Wind Direction, and Wind Speed. These forecasts will be for the CONUS as well as the 16 Overlapping CONUS Sectors and Puerto Rico. In order to take advantage of 2), you will have to go to "File->configure", and then Highlight the variables that you want to make active, and press the "Activate" button. Then you will have to go to the Sectors Tab, Highlight the Sectors that you want to make active, and press the "Activate" button. (Note: In previous versions of tkdegrib I did not have variables called "Wx" or "WaveHeight", I have now fixed that) 3) ***** I now have limited experimental GrADS support ***** (keep reading) ----------- I just wanted to let you all know that I have just finished putting together version "1.18" (last one that I announced was "1.17" on 6/2/2003). The latest version of the program is on: www.nws.noaa.gov/mdl/NDFD_GRIB2Decoder/ ***** GrADS support ***** 1) GrADS support: GrADS is a software package that has been around for a while, and is available for free from http://Grads.iges.org/. There is a PC version (the one I used), and several Unix versions and even a mac version. GrADS can take for input either GRIB1, NetCDF, or a binary file (it even claims to be able to convert to NetCDF). The binary file is the same as what I termed a ".flt file". The only thing that was lacking was a GrADS control file (or .ctl), which I am now producing. NOTE: GrADS usually uses unprojected data. When it starts dealing with what it considers "pre-projected" data, it interpolates the data to a lat/lon grid specified in the ASCII .ctl file. Almost all GRIB and GRIB2 grids are what GrADS considers "pre-projected", so one needs to provide information for GrADS to perform the projection. (for a better explanation see: http://Grads.iges.org/grads/gadoc/gadocindex.html :: "map projections".) THE FIRST CATCH: GrADS Hardwired a Radius of Earth = 6371.2 km. Most GRIB files use 6367.47 km, and NDFD is no exception. It is not currently possible to tell GrADS to use a different Radius of Earth. (For ArcView, I wrote an .ave script, which if used, sets the radius of earth correctly. Note you don't need it for the .shp files, just the .flt files). THE SECOND CATCH: GrADS does not have a mercator projection definition, and its north polar stereographic definition is prone to round off errors. I have set it to try using the lambert conformal conic projection for the mercator projection (since mercator is a special case of a lambert conformal conic projection). THE THIRD CATCH: GrADS on my PC version, when it tried projecting the NDFD lambert conformal conic grid, took forever and then ran out of buffer. SOLUTION: Use degrib (and tkddegrib's) Interpolate option. This will create a lat/lon grid with approximately the same coverage and resolution as the original grid, and GrADS works quite well with the interpolated grid. Example usage: "degrib ndfd.grib -C -msg 1 -Flt -Interp -GrADS" should create an interpolated .flt file and a .ctl file which GrADS can use. Remember you are interpolating here so you are not entirely true to the data (but you wouldn't be true to the data if GrADS interpolated for you.) Future: GrADS prefers to have all the data in a big data cube (similar to what NetCDF wants). Eventually I will get around to dumping the whole GRIB2 file to a data cube, instead of just wrapping the .flt file which is just a slice of the data cube. (Note potentially one could simply cat the .flt files together to create the cube, and modify the .ctl file a little). ----------- In other news... 2) I now allow one to call the program using "degrib <filename>" instead of requiring a -in option. 3) Fixed the timeout issue with regards to the http download method. 4) Added Wx and WaveHeight to tkdegrib. 5) Worked on Wave Height meta file support. ----------- As always, I tested this release on my PC (win 2000), a Linux machine, a HP-Unix machine, and an AIX-Unix (machine). Although I may have missed something in my testing, it should at least compile, and run for some of the test cases. For those of you with access to the NWS NCEP machine, my current version is in: /nfsuser/g06/we25at/degrib (on snow/frost, I'm no longer using asp/bsp). For those with access to MDL's GDP or NHDW machines, see: ~taylor/degrib/ Please let me know if you have problems. ----------- Regards, Arthur
|
||||||||||||||||||||||||||||||||||||||||||||||||||||
