Thank you Be for the good guide, however no luck with the syntax used namely;
ix0 = wherenearest( lower_left_lon_lat[1], lon )
ix1 = wherenearest( upper_right_lon_lat[1], lon )
iy0 = wherenearest( lower_left_lon_lat[2], lat )
iy1 = wherenearest( upper_right_lon_lat[2], lat )
# I end up with this error, "Error: could not find function "wherenearest"
Is there any other way I can get the index corresponding/or rearing to
thelongitude and latitude of interests? _____________
Peter E. Tuju
Dar es Salaam
T A N Z A N I A
----------------------
From: Ben Tupper <btup...@bigelow.org>
To: "r-help@r-project.org" <r-help@r-project.org>
Cc: Peter Tuju <petere...@ymail.com>
Sent: Saturday, January 9, 2016 4:01 PM
Subject: Re: [R] Extracting point data using longitude and latitude from
netcdf file using R
Hi,
This post gives more details on how to transform your lat/lon values to
row/column indices. The question and answer are specifically about the ncdf
package, but the workflow is identical when using the ncfd4 package.
https://stat.ethz.ch/pipermail/r-help/2011-March/272641.html
Cheers,
Ben
> On Jan 9, 2016, at 7:14 AM, Anthoni, Peter (IMK) <peter.anth...@kit.edu>
> wrote:
>
> Hi Peter,
>
> the start in nc_varget requires a latitude and longitude index, not the
> latitude and longitude in double format.
> So you need to figure out what index your latitude and longitude correspond
> to, which will depends on what data are in your netCDF.
>
> it might have looked like that it worked for a positive latitude, but you got
> the data from the latitude index 6 or 7, depends on how the double was
> transformed into an integer.
>
> best regards
> Peter
>
>> On 09 Jan 2016, at 12:28, Peter Tuju via R-help <r-help@r-project.org> wrote:
>>
>> I have data file in netcdf with three dimensions (x, y, t) and I want to
>> extract a variable RAINC and RAINNC
>> using longitude and latitude for a single point location with all the time,
>> but no lucky. The syntax is as follows;;
>> setwd( "/run/media/tuju/0767090047/extract_wrf_txt_file" )
>> rm( list = ls() )
>> library( ncdf4 )
>> inp_file <- nc_open( "wrfout_d01_2016-01-07.nc" )time <- ncvar_get(
>> inp_file, "Times" ) # Reading the time variabledar_lon
>> <- 39.2dar_lat <- -6.866667
>> RAINC <- ncvar_get( inp_file, varid = "RAINC", start = c( dar_lon, dar_lat,
>> 1 ), count = c( 1, 1, -1 ) )
>> RAINNC <- ncvar_get( inp_file, varid = "RAINNC", start = c( dar_lon,
>> dar_lat, 1 ), count = c( 1, 1, -1 ) )
>> RAIN <- RAINC + RAINNCRAIN_TABLE <- cbind( time, RAIN )
>> write.table( RAIN_TABLE, "Dar_es_Salaam.txt", row.names = FALSE,
>> col.names = c( "Valid Forecast Time", "Rain (mm)", sep = "\t " )
>>
>> # But no lucky with the red bolded syntax as I end up with the following
>> error message> RAINC <- ncvar_get( inp_file, varid = "RAINC", start = c(
>> Lon[2], Lat[2], 1 ), count = c( 1, 1, -1 ) )
>> Error in Rsx_nc4_get_vara_double: NetCDF: Index exceeds dimension bound
>> Var: RAINC Ndims: 3 Start: 0,4294967289,38 Count: 17,1,1
>> Error in ncvar_get_inner(ncid2use, varid2use, nc$var[[li]]$missval,
>> addOffset, :
>> C function R_nc4_get_vara_double returned error
>> However when I cahnge the latitude to postive it works fine. Note latitudes
>> in the file data ranges from -16.71505 to 7.787529 as shown below;
>> head(ncvar_get(inp_file, "XLAT"))
>> [1] -16.71505 -16.71505 -16.71505 -16.71505 -16.71505 -16.71505
>>> tail(ncvar_get(inp_file, "XLAT"))
>> [1] 7.787529 7.787529 7.787529 7.787529 7.787529 7.787529
>> ## So, how can I get the syntax correct? Please help _____________
>> Peter E. Tuju
>> Dar es Salaam
>> T A N Z A N I A
>> ----------------------
>>
>>
>>
>>
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
