| Finding pixel values of NETCDF image based on lat/lon [message #89066] |
Mon, 21 July 2014 20:46  |
Marta Yebra
Messages: 16
Registered: August 2012
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Junior Member |
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Hi all,
I am just introducing myself to NETCDF format and I have been able to read and access the data but Now I need to extract a time-serie of the values for a point location (lat/lon) and I do not know how to do it.
This is my piece of bad coding :):
filename='C:\UserData\yebram\GPP\2014516145028EnsembleGPP_GL .nc'
file_sites='C:\UserData\yebram\GPP\Sites_locations.csv'
;1. Open the file and assign it a file ID
NCDF_Id = ncdf_open(filename)
;When you are completely through with the file you should close it using the ncdf_close, fileID command.
;2. Find the number of file attributes and datasets (or variables). The information will be contained in the structure variable that we have named 'fileinq_struct',
;but you may give it any name you wish so long as you use the proper record names.
fileinq_struct=ncdf_inquire(NCDF_Id)
Ndims=fileinq_struct.Ndims ;The number of dimensions defined for this NetCDF file.
nvars = fileinq_struct.nvars ;The number of variables defined for this NetCDF file.
ngatts = fileinq_struct.ngatts ;The number of global attributes defined for this NetCDF file
RecDim=fileinq_struct.RecDim; The ID of the unlimited dimension, if there is one, for this NetCDF file. If there is no unlimited dimension, RecDim is set to -1.
; retrieve GPP data
; units = "kg m-2 s-1";
; _FillValue = -9999.0f; // float
; float gpp(time=360, lat=360, lon=720);
nameGPP='gpp'
NCDF_VARID_GPP = NCDF_VARID(NCDF_Id, nameGPP)
NCDF_VARGET, NCDF_Id, NCDF_VARID_GPP, GPP
GPP[where(GPP eq -9999)] = !VALUES.F_NAN
; retrieve long data
; units = "degrees_east";
nameLon='lon'
NCDF_VARID_lon = NCDF_VARID(NCDF_Id, nameLon)
NCDF_VARGET, NCDF_Id, NCDF_VARID_lon, Lon
Lon[where(Lon eq -9999)] = !VALUES.F_NAN
; retrieve lat data
; units = "degrees_north";
nameLat='lat'
NCDF_VARID_lat = NCDF_VARID(NCDF_Id, nameLat)
NCDF_VARGET, NCDF_Id, NCDF_VARID_lat, lat
lat[where(lat eq -9999)] = !VALUES.F_NAN
; retrieve time data
; units = "days since 1582-10-14 00:00:00";
; calendar = "standard";
nameTime='time'
NCDF_VARID_Time = NCDF_VARID(NCDF_Id, nameTime)
NCDF_VARGET, NCDF_Id, NCDF_VARID_Time, Time
Time[where(Time eq -9999)] = !VALUES.F_NAN
;open file with coordinates for teh sites
my_data=read_csvok(file_sites)
sites=my_data.Name_site
Lat_sites=my_data.Lat
Lon_sites=my_data.Lon
find_lon=where(Lon EQ Lon_sites, countlon)
find_lat=where(Lat EQ Lat_sites, countLat)
but this cannot find anything since my coordinate is for example 41.160000 and that value is not in the NETCDF.
How can I select the pixel that contains my point?
Your help is very much appreciate.
Kind regards,
Marta
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