On Jan 9, 2016, at 7:14 AM, Anthoni, Peter (IMK) <peter.anthoni at 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 at 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
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