Need help converting ascii to netcdf files
Added by Mengli Wei over 8 years ago
Hello to all,
I'm trying to build a hydrologic model, for which I downloaded the daily evapotranspiration data from DWD, all files in ascii format, in the form of a matrix of 654x866 pixels, 1 km cell size. I attached the description file and an ascii file.
I would very much appreciate it if anyone could tell me how to convert this ascii file into a netcdf file. I tried many times using the input command, but the problem is that I don't know how to set up a valid grid or a grid description for my purpose.
At first I used the command "cdo -f nc input,r654x866 out.nc in.asc", however, it turned out to be totoally wrong. I lost all the data after using sellonlatbox command.
Then I generated a grid file, which is also attached (mygrid), hoping the xvals and yvals could appear automatically. Proved me wrong again. I got the nc file with all the data but without lat lon. Neither setgrid nor setgridtype could help in this situation.
I also tried using another grid description, which I got with the griddes command applied to a precipitation file of the entire Germany, with both xsize and ysize = 1200. It didn't work because of "too few input elements".
Now I am stuck... Any suggestions would be so much appreciated!
Many thanks in advance and best wishes,
Mengli
Replies (4)
RE: Need help converting ascii to netcdf files - Added by Ralf Mueller over 8 years ago
Examples for griddes files can be created with the griddes operators:
ram@luthien:~ cdo griddes -remapnn,r180x80 -topo [11:33:03|15-09-10] cdo griddes: Started child process "remapnn,r180x80 -topo (pipe1.1)". cdo(2) remapnn: Started child process "topo (pipe2.1)". cdo(3) topo: Set default filetype to GRIB # # gridID 1 # gridtype = lonlat gridsize = 14400 xname = lon xlongname = longitude xunits = degrees_east yname = lat ylongname = latitude yunits = degrees_north xsize = 180 ysize = 80 xfirst = 0 xinc = 2 yfirst = -88.875 yinc = 2.25
For a curviliear grid, this looks different, see attachement:curvi-griddes.txt
All locations have to be given in lon lat, not in meters. If you do not want to regrid, compute area weights or anything that involves coordinated, they might be set some unrealistic values. But pay attention on what operators you're using.
If that does not work, I recomment to write the netcdf manually with e.g. python-netcdf4 bindings: https://netcdf4-python.googlecode.com/svn/trunk/docs/netCDF4-module.html or http://www-pord.ucsd.edu/~cjiang/python.html
| curvi-griddes.txt (1.44 MB) curvi-griddes.txt |
RE: Need help converting ascii to netcdf files - Added by Mengli Wei over 8 years ago
Hello Ralf,
thank you for your quick answer!
I did the conversion again with following command:
cdo -f nc input,grid 19910101.nc < grids_germany_daily_evapo_p_19910101.asc
It turned out that the data were kept, somehow the nc file generated 322 timesteps, which is weird, because the original data is daily.
Could you please have a look at attached files to see what I did wrong? Many many thanks for your help!
Best wishes,
Mengli
| 19910101.nc (2.19 MB) 19910101.nc | |||
| grid (44 KB) grid |
RE: Need help converting ascii to netcdf files - Added by Ralf Mueller over 8 years ago
you text input describes
- a single timestep of a 654x866 gridpoints grid or
- 866 timesteps on a 654 points grid or
- 654 timesteps on a 866 points grid or ....
your grid desciption defines a 42x42 points grid
IMO this does not fit together.
I did some tests and wrote in little python script, which reads in your text file
You can just call
python txt2nc.py
I changed the header information in the txt input, but not much
hth
ralf
| fromTxt.nc (2.17 MB) fromTxt.nc | output of python script | ||
| in.txt (3.24 MB) in.txt | little reformated text input | ||
| txt2nc.py (640 Bytes) txt2nc.py | python script to create the nc file |
RE: Need help converting ascii to netcdf files - Added by Mengli Wei over 8 years ago
Hi Ralf,
thank you, your script helped me a great deal! It's very kind of you 
Best wishes,
Mengli