Extract multi value points using CDO into a single text file-CodePudding

I have come across the code

cdo -outputtab, date,value -remapnn,lon=X/lat=Y infile.nc > Outfile.txt

which very nicely extracts for a single point only. Is there any way I can extract time series data from netcdf file for multiple points using a single command line or by using some script and get the output in a single text file? Something like this -

lat-lon1, lat-lon2, lat-lon3

235, 256, 254

264, 246, 249

289, 278, 259

......

CodePudding user response：

You can solve this in Python using my package nctoolkit, which uses CDO as a backend. Code would be something like the following:

import pandas as pd
import nctoolkit as nc
# load data
ds = nc.open_data("in.nc")
# define coords you want to regrid to
coords = pd.DataFrame({"lon":[0, 10, 20], "lat":[0, 10, 20]})
# regrid using nn
ds.regrid(coords, "nn")
# convert to pandas df
df = ds.to_dataframe()

Under the hood this will generate a single grid file based on the specified coordinates and then call CDO once to do the regridding, so should be computationally efficient.

CodePudding user response：

I'm not sure why you tagged a cdo command equiry with python, are you looking for a bash command script solution or a python code?

If you want a simple bash script then you can do this using a loop over lat lon pairs to produce a set of text files and then combine then column-wise using this solution here.

Note 1: I drop the "date" otherwise you will have the date repeated for each entry - if you must have the date then pull out the first cdo remap command from the loop and do that one including "date".

Note 2: This will be space separated and not comma separated - I'm assuming that is not an issue

# these are LON/LAT pairs:
for i in "10 3" "2 5" "3 7"; do 
   a=( $i )
   lon=${a[0]}
   lat=${a[1]}
   cdo -outputtab,value -remapnn,lon=${lon}/lat=${lat} infile.nc > pt_lon${lon}_lat${lat}.txt
   # change column title from "value" to "lon-lat vals"  
   sed -i -e "s/value/${lon}-${lat}/" pt_lon${lon}_lat${lat}.txt
done
# now combine the columns - set the e24 to the width that is appropriate
paste pt_*.txt  | pr -t -e24