Importing and exporting data

NCL supports import and export for several data types including netCDF and HDF. Here is a list of supported operations:

• netCDF import
• netCDF export
• GRIB import
• HDF import
• HDF export
• binary file import
• binary file export
• ASCII file import
• ASCII file export

ASCII files

Import

-1. 0. 1. 2.

input_data = asciiread("float_data",4,"float")
print(input_data)

yields:

Variable: input_data
Type: float
Total Size: 16 bytes
            4 values
Number of Dimensions: 1
Dimensions and sizes:   [4]
Coordinates: 
Number Of Attributes: 1
_FillValue 
(0)     -1
(1)     0
(2)     1
(3)     2

 1 <--First data item, 2 <--Second data item
 3, 4,
 5XXX6YYY

input_data = asciiread("int_data",(/2,3/),"integer")
print(input_data)

yields:

Variable: input_data
Type: integer
Total Size: 24 bytes
            6 values
Number of Dimensions: 2
Dimensions and sizes:   [2] x [3]
Coordinates: 
Number Of Attributes: 1
_FillValue 
(0,0)   1
(0,1)   2
(0,2)   3
(1,0)   4
(1,1)   5
(1,2)   6

Export

a = (/1,2,3/)
asciiwrite("int_file",a)

1
2
3

Binary files

Import

fval = cbinread("c_bin_data",3,"float")

Note: The data file read in by cbinread must have been created on a machine of the same architecture as the one that NCL is being run on. For example, if you created a binary file on a machine with a 64-bit word size and tried to read it back on a 32-bit machine, you will not get what you want.

Binary files created using Fortran unformatted writes can be imported directly into NCL by using the NCL fbinread function. For example, if "f_bin_data" is a binary file as described that contains three floating point numbers, then the NCL command

fval = fbinread("f_bin_data",3,"float")

Note: The data file read in by fbinread must have been created on a machine of the same architecture as the one that NCL is being run on.

Export

fval = (/ 1., 2., 3. /)
cbinwrite("c_bin_data",fval)

Writing binary files using a Fortran unformatted write with fbinwrite is entirely analogous to using cbinwrite.

netCDF files

Import

As an example, suppose the file "simple.cdl" (cdl files are ASCII versions of netCDF files that can be converted to netCDF files by using the netCDF library function ncgen) contains the following simple file:

netcdf simple {  // A very simple file for demo purposes.

dimensions:
    xdim = 5;

variables:

    float       xarray(xdim);
                xarray:long_name = "A small array";
                xarray:units = "dimensionless";
                xarray:valid_range = 0.f, 7.f ;
                xarray:_FillValue = -9999.0f;

    float       xdim(xdim);
                xdim:long_name = "X array dimension";
                xdim:units = "dimensionless";

    :history = "created by SCD for demo purposes";
    :title = "Simple demo";

data:

 xdim = -20, -10,   0,  10,  20;

 xarray = -1., 0., 1., 2., 3.;
}

ncl 0> file1 = addfile("simple.cdf","r")
ncl 1> print (file1)

filename:       simple
path:   simple.cdf
        dimensions:
                xdim = 5
        variables:
                float xarray(xdim)
                float xdim(xdim)
ncl 2> print(file1->xarray)


Variable: xarray (file variable)
Type: float
Total Size: 20 bytes
            5 values
Number of Dimensions: 1
Dimensions and sizes:   [xdim | 5]
Coordinates: 
            xdim: [xx..xx]
Number Of Attributes: 4
long_name 
units 
valid_range 
_FillValue 
(0)     -1
(1)     0
(2)     1
(3)     2
(4)     3
ncl 3> print(file1!0)
(0)     xdim
ncl 4> print(file1@history)
(0)     created by SCD for demo purposes
ncl 5> print(file1->xarray({-10:10}))


Variable: xarray (file variable subsection)
Type: float
Total Size: 12 bytes
            3 values
Number of Dimensions: 1
Dimensions and sizes:   [xdim | 3]
Coordinates: 
            xdim: [xx..xx]
Number Of Attributes: 4
long_name 
units 
valid_range 
_FillValue 
(0)     0
(1)     1
(2)     2

Export

ncl 0> file1 = addfile("file1.cdf","c")
ncl 1> file1->xarray = (/2.,3.,4.,5.,6./)
ncl 2> file1!0 = "xdim"
ncl 3> file1&xdim = (/-20,-10,0,10,20/)
ncl 4> file1->xarray@units = "millimeters"
ncl 5> file1@title = "NCL-created netCDF"
ncl 6> quit

netcdf file1 {
dimensions:
        xdim = 5 ;

variables:
        float xarray(xdim) ;
                xarray:units = "millimeters" ;
        long xdim(xdim) ;

// global attributes:
                :title = "NCL-created netCDF" ;

data:

 xarray = 2 , 3 , 4 , 5 , 6  ;

 xdim = -20, -10, 0, 10, 20 ;
}

HDF files

Import

Export

Also there is currently no way to access 8 bit and 24 bit HDF images from NCL.

GRIB import

User Guide Control Panel

NG4.1 Home, Index, Examples, Glossary, Feedback, UG Contents, UG WhereAmI?