Wgrib2 convert grib2 to netcdf
Site Map. CPC Search. You've been warned. My second use of this option wgrib2 v2. There were bug fixes and the ability to import values stored in bytes and integers. The grib2 compression was extremely good, using only 0. The grib compression was good because one field was a mask, ice concentration was mostly zero value, and the SST and SST error where undefined over land and lakes.
[netCDF #HOT-122007]: converting grib2 files to netcdf using wgrib2 -netcdf
The grid point values were unchanged in the conversion from netcdf to grib because both the netcdf and grib files used the same precision. Introduction Reading netcdf is easy if someone else wrote the program to read the netcdf file. Writing the code to read netcdf is something else.
A netcdf file can contain many variables. In my sample file, there is one data varable "acpcp" and and 6 supporting variables. Geopotential height can have units of meters, metres, inches, microns, nautical miles, chains, rods or any unit of length in any language necdf supports unicode.
The joys of standards that don't set standards. Netcdf is a standard but fails to standardize units of length. Variables in netcdf can be viewed as variable dim-i,dim-j. For example, in one dataset, X could be one-dimensional, latitude could be two dimensional and temperature could be 4 dimensional.
There is netcdf library code to read varaible i0:i1, j0:j1. The code reads the data and uses it to overwrite the wgrib2's data register. As a first step, I want to list the variables in the netcdf file. As expected, "asd" is not a valid varaible, and I get an error message and the desired list of valid variables. Tutorial: Unknown attributes and dimensions of a variable To get a variable description, you need to try to import a netcdf file.
From the attributes, we see that the variable is a 3 hour accumulated convective precipitation. Wgrib2 is using the C interface to the netcdf library. So C conventions apply.This kitchen miracle was done by a more developer friendly design and the contributions of many people. Some functionality include. OpenMP is used to speed up wgrib2 by running loops over multiple cores.
With gcc and icc, OpenMP is on by default. In general, you set the number of threads to be less or equal to the number of CPU cores available. Usually I set the number to 3 on a quad-core machine. That leaves one core for unrelated work. After you download hdf Then you may be able to compile wgrib2 with netCDF4 support.
Seg-faults are pretty uncommon to wgrib2. The jpeg library Jasper could seg-fault with larger grids. If your copy of wgrib2 is using another version of the Jasper library, then your copy of wgrib2 may be vunerable to this problem.
Wgrib2 can decode grib using g2clib. Using the g2clib that was not included with the wgrib2 sorc code is could cause a seg-fault. Wgrib2 had patches to g2clib that were not fully incorporated until g2clib v1.
In addition, g2clib can be compiled either with a 32 or bit interface. The default makefile assumes that a bit interface is used on bit processors and a bit interface is used bit processors. Third-parties often followed NCEP's lead and used a bit interface on bit processors and a bit interface on bit processors. Finallyl, the third problem is a compiler bug and only affects wgrib2 v2. The problem is fixed by gcc 2. There a potential for seg-faults by reading using specially crafted png or jpeg compressed grib files.
For example, a few days after the release of wgrib2 v2. Bug reports are important Contact wesley. For example, you selected the winds and temperatures. You can use the "if" to send the winds to one file and the temperatures to another file. The conversion uses a user-selected interpolation scheme: bilinear defaultbicubic, nearest neighbor and budget. Note: the interpolation uses scalar and vector interpolation schemes. For the vector quantities the V field must immediately follow the corresponding U field.One of the strengths of GRIB is its ability to store data compactly.
For each 2D slice to store, the range min, max of the data along with the number of bits to store N determines a scale and offset, which is used to convert the floating point value to an N-bit integer. Deflate is a lossless dictionary encoder, which looks for patterns in the data and stores common patterns efficiently. A completely random set of numbers won't have patterns, and so will not compress. Floating point data can be difficult to compress because the lower bits of the mantissa are essentially random.
However, the GRIB data already has those random bits removed when its converted from floating point to N-bit integers. So there's hope that deflate might do a good job on GRIB data. When using deflate, you can choose deflate levels ofwith 0 meaning no compression and 9 being the highest compression, with corresponding trade-offs with the time it takes to compress.
HDF-5 also offers a "shuffle" option which rearranges the bytes of the data to make the data compress better. This chart plots the compression ratio bigger is better of the resulting file against the time to rewrite the entire file read GRIB, compress, write netCDF I used the netCDF-Java library version 4. Tests on other files lead me to believe this result is typical. The time of the first point of the shuffle data is an artifact of the file cache spin-up.
Deflate levels greater than 4 don't seem to make the file much smaller for the extra time spent compressing level 9 was off the chart. In conclusion, for these kinds of files at least, don't use the shuffle filter and use a deflate level of Main Part 2: Converting Email this. Take a poll! What if we had an ongoing user poll in here? Search by Tag ar-4 ar-5 awips cache caron cdm cf chunking compression coordinates dap4 grib hdf5 idv intern java license metpy metpymonday nczarr netcdf netcdf-4 netcdf4 opuls performance python release siphon tds toolsui.
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I use a software named tkdegrib but it catches one argument by one argument whereas I want all my grib's arguments in the same file. Unfortunately, I can't use Linux. And since it's Java, you don't have to build anything, and it works on all platforms.
There is a ToolsUI application that you can use if you want a GUI, but more likely you want to do it from the command line using something like this:. UPDATE If you have Windows 10, it is now much easier to simply install ubuntu directly under windows as a subsystem no wineserver requiredand then you can install CDO very easily with. ECMWF has developed a new package called eccodes which includes command line operators for this kind of task.
This is the preferred method if you have grib data with more than one time axis such as S2S output, where you have the time of the forecast start and the forecast step and possibly even the hindcast start date. In those cases CDO fails. For more options of this utility can be searched on this link. Learn more. Convert grib to netcdf file Ask Question. Asked 6 years, 9 months ago. Active 1 month ago. Viewed 5k times. Adrian Tompkins 2, 1 1 gold badge 11 11 silver badges 42 42 bronze badges.
Active Oldest Votes. There is a ToolsUI application that you can use if you want a GUI, but more likely you want to do it from the command line using something like this: java -Xmxm -classpath netcdfAll NetcdfDataset -in infile. Rich Signell Rich Signell Does this compress the resulting NetCDF file? Does it do that by default? Climate data operators If you have cygwin installed you can use CDO: cdo -f nc copy file.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I tried codes like this:. Learn more. Asked 4 months ago. Active 4 months ago. Viewed 40 times. Lingling Lingling 1 3 3 bronze badges. Please edit the question and explain what "it does not work" means. Do you get an error message? What does it say?
Something unexpected happens? The error message, if any, often contains clues about what's wrong.
I got error messages like this. So, what are valid file names? Do you have a file that starts with api-ms-win-core-synch-l Add this information to the question body.
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What I need overall is to generate image for ocean current components available in netCDF and display on map. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Asked 6 years, 4 months ago. Active 4 years, 5 months ago. Viewed 3k times. Michael B 4 4 silver badges 22 22 bronze badges. Anil Anil 93 1 1 silver badge 10 10 bronze badges. Active Oldest Votes. Dave X Dave X 6 6 silver badges 17 17 bronze badges.
What is the problem when you try to read a netcdf file in grads? The command in grads to read netcdf file is sdfopen filename. Roberto Santos Roberto Santos 6 6 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name.
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What are GRIB files
Sign in to your account. I am using netcdf4-python to handle my grib2 format data reading and writing. I have to convert my data to netcdf format by using wgrib2 from:. I have written some mails with the author of wgrib2. According to the reply from support-netcdf unidata. I know scitools-iris can handle this kind of task but it is to heavy for my case.
There are python grib readers out there pygrib for example. I think it's the domain of a third party app to translate the grib variables and metadata to netcdf-like data structures, and then write out to netcdf. I don't think this really belongs in netcdf4-python. It would be great if someone would translate the netcdf-java code for doing this into python. It's not an easy or quick task though.
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So will netcdf4-python add grib format support in the future? This comment has been minimized. Sign in to view. Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment. Linked pull requests.