[ferret_users] reading a small portion of stream binary file

[Ryo Furue <furue@xxxxxxxxxx>]

Dear Ferret users,

I'm trying to read a small portion of a huge binary file but have failed to do so far.  Here is the relevant quote from the Ferret manual:

When reading from stream or binary files, the entire grid is read when the data is requested.  To read subsets of the data, define a smaller grid to read a subset of records and perhaps write that out to a netCDF file, then do a second read, skipping those first records, and so on.

(from https://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/data-set-basics/BINARY-DATA )

So, as a test, I was trying to read only the initial 10 elements, like so:

define axis/x=0:9:1 xax
define grid/x=xax mygrid
file/grid=mygrid/var=temp/form=stream/type=r8 temp0-rot-pntd.bin

list temp

When I run the above program (pyferret -nodisplay -script try-slices.jnl), I get this error

 **ERROR: Size of file ./temp0-rot-pntd.bin doesn't match size specified by variables/grid
list temp
Command file, command group, or REPEAT execution aborted
           *** NOTE: Binary file reading: Insufficient memory reading variable    2

The above script works when the binary file is not huge.  So, it seems that Ferret tries to read the whole thing.

It's PyFerret v7.5 on Linux.

Ryo