Ross Bannister, Dept. of Meteorology, University of Reading, UK
A. Operations to read-in netCDF data (no attributes)1. Open the netCDF file (NF_OPEN). 2. Get dimension IDs (NF_INQ_DIMID) - one per dimension. 3. Get dimension lengths (NF_INQ_DIMLEN) - one per dimension. 4. Get variable IDs (NF_INQ_VARID) - one for each dimension present and per data variable required. 5. Define the 'shape' of the data to be input. 6. Read-in the data (NF_GET_VARA_REAL) - repeat steps 5 and 6 for each variable (including dimension variables). 7. Close the netCDF file (NF_CLOSE). |
B. Operations to write netCDF data (no attributes)1. Open the netCDF file (NF_CREATE). 2. Define the dimensions (NF_DEF_DIM) - one per dimension. 3. Define the variables (NF_DEF_VAR) - one for each dimension present and per data variable to be output. 4. Change the mode of netCDF operation (NF_ENDDEF). 5. Define the 'shape' of the data to be output. 6. Output the values of the variables (NF_PUT_VARA_REAL) - repeat steps 5 and 6 for each variable (including dimension variables). 7. Close the netCDF file (NF_CLOSE). |
C. Compilation on the Sun systeminclude file: '/opt/local/include/netcdf.inc'
Compilation: f77 filename.f /opt/local/lib/libnetcdf.a |
All routines are integer functions in FORTRAN.
NF_OPEN (path, mode, ncid)
path char. string input File name of netCDF file
mode integer input NF_WRITE or NF_NOWRITE
ncid integer output ID index of netCDF file
NF_CREATE (path, cmode, ncid)
path char. string input File name of netCDF file
cmode integer input NF_SHARE or NF_NOCLOBBER
ncid integer output ID index of netCDF file
NF_INQ_DIMID (ncid, name, dimid)
ncid integer input ID index of netCDF file
name char. string input Name of dimension
dimid integer output ID index of dimension
NF_INQ_DIMLEN (ncid, dimid, len)
ncid integer input ID index of netCDF file
dimid integer input ID index of dimension
len integer output Length of dimension
NF_INQ_VARID (ncid, name, varid)
ncid integer input ID index of netCDF file
name char. string input Name of variable
varid integer output ID index of variable
NF_GET_VARA_REAL (ncid, varid, start, count, rvals)
ncid integer input ID index of netCDF file
varid integer input ID index of variable
start integer(n) input index vector of position to start reading
count integer(n) input lengths of 'volume' to be retrieved
rvals real(x,y,...) output data structure to hold data
n=dimensionality of variable (this is 1 for simple dimension variables).
NF_DEF_DIM (ncid, name, len, dimid)
ncid integer input ID index of netCDF file
name char. string input Name of dimension
len integer input Length of dimension (units)
dimid integer output ID index of dimension
NF_DEF_VAR (ncid, name, xtype, ndims, dimids, varid)
ncid integer input ID index of netCDF file
name char. string input Name of variable
xtype integer input NF_BYTE, NF_CHAR, NF_REAL, ...
ndims integer input Number of dimensions (1-4)
dimids integer(4) input List of dimension IDs (first ndims elements only)
varid integer output ID index of variable
NF_ENDDEF (ncid)
ncid integer input ID index of netCDF file
NF_PUT_VARA_REAL (ncid, varid, start, count, rvals)
ncid integer input ID index of netCDF file
varid integer input ID index of variable
start integer(n) input index vector of position to start writing
count integer(n) input lengths of 'volume' to be output
rvals real(x,y,...) input data structure holding data
n=dimensionality of variable (this is 1 for dimension variables).
NF_CLOSE (ncid)
ncid integer input ID index of netCDF file
* 789012345678901234567890123456789012345678901234567890123456789012
* ^ 1 2 3 4 5 6 7 ^
* ==================================================================
* Attempt to read-in some netCDF data
program ReadIn
integer ncid,ierr,dimidx,dimidy,dimidz,dimidt,varid,varidx,varidy
integer varidz,varidt,startA(1),countA(1),startB(4),countB(4)
integer lenx,leny,lenz,lent
real valsx(96),valsy(72),valsz(25),valst(1),vals(96,72,25,1)
* Declare functions and variables associated with the netCDF library
integer NF_OPEN,NF_NOWRITE,NF_INQ_DIMID,NF_INQ_VARID,NF_INQ_DIMLEN
integer NF_GET_VARA_REAL,NF_CLOSE
include '/opt/local/include/netcdf.inc'
* 1. Open the netCDF file
* -----------------------
ierr=NF_OPEN('/twix/AMIPII/amip2_mmean/amip2_mmean_jan79.nc',
+ NF_NOWRITE,ncid)
print*,1,ierr
* 2. Get dimension IDs
* --------------------
ierr=NF_INQ_DIMID(ncid,'longitude_72x96',dimidx)
print*,2,ierr
ierr=NF_INQ_DIMID(ncid,'latitude_72x96',dimidy)
print*,3,ierr
ierr=NF_INQ_DIMID(ncid,'dp25',dimidz)
print*,4,ierr
ierr=NF_INQ_DIMID(ncid,'time',dimidt)
print*,5,ierr
* 3. Get dimension lengths
* ------------------------
ierr=NF_INQ_DIMLEN(ncid,dimidx,lenx)
print*,6,ierr
ierr=NF_INQ_DIMLEN(ncid,dimidy,leny)
print*,7,ierr
ierr=NF_INQ_DIMLEN(ncid,dimidz,lenz)
print*,8,ierr
ierr=NF_INQ_DIMLEN(ncid,dimidt,lent)
print*,9,ierr
print*,'Dimension lengths',lenx,leny,lenz,lent
* 4. Get variable IDs
* -------------------
* First the variables for the dimensions
ierr=NF_INQ_VARID(ncid,'longitude_72x96',varidx)
print*,6,ierr
ierr=NF_INQ_VARID(ncid,'latitude_72x96',varidy)
print*,7,ierr
ierr=NF_INQ_VARID(ncid,'dp25',varidz)
print*,8,ierr
ierr=NF_INQ_VARID(ncid,'time',varidt)
print*,9,ierr
* ...and for the main data variable
ierr=NF_INQ_VARID(ncid,'ta',varid)
print*,10,ierr
* 5. Get contents of dimension variables
* --------------------------------------
startA(1)=1
countA(1)=lenx
ierr=NF_GET_VARA_REAL(ncid,varidx,startA,countA,valsx)
print*,11,ierr
startA(1)=1
countA(1)=leny
ierr=NF_GET_VARA_REAL(ncid,varidy,startA,countA,valsy)
print*,12,ierr
startA(1)=1
countA(1)=lenz
ierr=NF_GET_VARA_REAL(ncid,varidz,startA,countA,valsz)
print*,13,ierr
startA(1)=1
countA(1)=lent
ierr=NF_GET_VARA_REAL(ncid,varidt,startA,countA,valst)
print*,14,ierr
print*,'longitude values'
print 100,(valsx(l),l=1,lenx)
print*,'latitude values'
print 100,(valsy(l),l=1,leny)
print*,'pressure values'
print 100,(valsz(l),l=1,lenz)
print*,'time values'
print 100,(valst(l),l=1,lent)
* 6. Get values of the main variable
* ----------------------------------
startB(1)=1
startB(2)=1
startB(3)=1
startB(4)=1
countB(1)=lenx
countB(2)=leny
countB(3)=lenz
countB(4)=lent
ierr=NF_GET_VARA_REAL(ncid,varid,startB,countB,vals)
print*,15,ierr
* 7. Close the file up
* --------------------
err=NF_CLOSE(ncid)
print*,16,ierr
* 8. Output a pressure level to gnuplot
* -------------------------------------
open (12,file='Gnu1')
do l=1,lenx
do m=1,leny
write (12,101) vals(l,m,20,1)
enddo
if (l.lt.lenx) write (12,102)
enddo
close (12)
print*,'Pressure level',valsz(20),' output for gnuplot'
100 format (100F8.2)
101 format (F12.6)
102 format ((A))
end
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* 789012345678901234567890123456789012345678901234567890123456789012
* ^ 1 2 3 4 5 6 7 ^
* ==================================================================
* Attempt to write out some netCDF data
program netcdf2
integer err,fileid,dimidx,dimidy,dd(4),varidx,varidy,myvar
integer startA(1),startB(2),countA(1),countB(2)
real xvals(100),yvals(50),var(100,50)
* netCDF functions
integer NF_CREATE,NF_CLOBBER,NF_DEF_DIM,NF_REAL,NF_ENDDEF
integer NF_PUT_VARA_REAL,NF_CLOSE
include '/opt/local/include/netcdf.inc'
* Open a netCDF file
err=NF_CREATE('Test2.nc',NF_CLOBBER,fileid)
* Define the dimensions
err=NF_DEF_DIM(fileid,'xval',100,dimidx)
err=NF_DEF_DIM(fileid,'yval',50,dimidy)
* Define the variables (include 2 variables giving the dim. values)
dd(1)=dimidx
err=NF_DEF_VAR(fileid,'xval',NF_REAL,1,dd,varidx)
dd(1)=dimidy
err=NF_DEF_VAR(fileid,'yval',NF_REAL,1,dd,varidy)
dd(1)=dimidx
dd(2)=dimidy
err=NF_DEF_VAR(fileid,'MyVar',NF_REAL,2,dd,myvar)
print*,'x dim ID ',dimidx
print*,'y dim ID ',dimidy
print*,'x var ID ',varidx
print*,'y var ID ',varidy
print*,'main ID ',myvar
* Change mode of netCDF operation
err=NF_ENDDEF(fileid)
* Output the values of the variables (include dimension variables)
* x dimension values
startA(1)=1
countA(1)=100
do l=1,100
xvals(l)=2.0*real(l)
enddo
err=NF_PUT_VARA_REAL(fileid,varidx,startA,countA,xvals)
* y dimension values
startA(1)=1
countA(1)=50
do l=1,50
yvals(l)=real(l)/2.0
enddo
err=NF_PUT_VARA_REAL(fileid,varidy,startA,countA,yvals)
* Main variables values
startB(1)=1
startB(2)=1
countB(1)=100
countb(2)=50
do l1=1,100
do l2=1,50
var(l1,l2)=sin(0.1*real(l1)+0.3*real(l2))
enddo
enddo
err=NF_PUT_VARA_REAL(fileid,myvar,startB,countB,var)
* CLose the file up
err=NF_CLOSE(fileid)
end
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* 789012345678901234567890123456789012345678901234567890123456789012
* ^ 1 2 3 4 5 6 7 ^
* ==================================================================
* Attempt to read in the netCDF data written by netCDF2
program netcdf3
integer err,fileid,dimidx,dimidy,dd(4),varidx,varidy,myvar
integer startA(1),startB(2),countA(1),countB(2),lenx,leny
real xvals(100),yvals(50),var(100,50)
* netCDF functions
integer NF_CREATE,NF_CLOBBER,NF_DEF_DIM,NF_REAL,NF_ENDDEF
integer NF_PUT_VARA_REAL,NF_CLOSE,NF_OPEN,NF_NOWRITE,NF_INQ_DIMID
integer NF_INQ_DIMLEN,NF_INQ_VARID,NF_GET_VARA_REAL
include '/opt/local/include/netcdf.inc'
* Open the netCDF file for reading
err=NF_OPEN('Test2.nc',NF_NOWRITE,fileid)
* Get dimension IDs
err=NF_INQ_DIMID (fileid,'xval',dimidx)
err=NF_INQ_DIMID (fileid,'yval',dimidy)
* Get dimension lengths
err=NF_INQ_DIMLEN (fileid,dimidx,lenx)
err=NF_INQ_DIMLEN (fileid,dimidy,leny)
print*,'Length of x-dimension',lenx
print*,'Length of y-dimension',leny
* Get variable IDs
err=NF_INQ_VARID (fileid,'xval',varidx)
err=NF_INQ_VARID (fileid,'yval',varidy)
err=NF_INQ_VARID (fileid,'MyVar',myvar)
* Get contents of dimension variables
startA(1)=1
countA(1)=100
err=NF_GET_VARA_REAL (fileid,varidx,startA,countA,xvals)
startA(1)=1
countA(1)=50
err=NF_GET_VARA_REAL (fileid,varidy,startA,countA,yvals)
print*,'Here are the x-values'
print 100,(xvals(l),l=1,100)
print*,'Here are the y-values'
print 101,(yvals(l),l=1,50)
* Get the main data (what all of this is actually for!!)
startB(1)=1
startB(2)=1
countB(1)=100
countb(2)=50
err=NF_GET_VARA_REAL (fileid,myvar,startB,countB,var)
* Close the netCDF file
err=NF_CLOSE(fileid)
* Output the data so that gnuplot can look at it
open (12,file='gnudata')
do l1=1,100
do l2=1,50
write (12,102) var(l1,l2)
enddo
if (l1.lt.100) write (12,103)
enddo
close (12)
100 format (100F8.2)
101 format (50F8.2)
102 format (F12.6)
103 format ((A))
end
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