[ferret_users] Re: depth coordinate (inverted vertical axis)

[Ryo Furue <furue@xxxxxxxxxx>]

Hi Ferret users,

I asked this question a while ago:

> I'm wondering how to associate depth coordinate values
> with a binary datafile which has this structure:
>
>   k = 1    --- 1000m depth
>   k = 2    ---  990m depth
>   . . . .
>   k = 101  ---    0m

to which Steve Guimond suggested a solution.  With his
permission, I quote part of his message.

|   Just a thought, but maybe you could try flipping the z axis using
| the /order qualifier such as :
| 
| use/order=y-z my_file.nc
| 
| You could make your grid with the depth axis as is, then save to a 
| netcdf file, and reopen with the line above. [...]

In fact, his solution works excellently.

  1) Open the original stream binary file;
  2) Save it as a netCDF file without changing axes or anything;
  3) Open the netCDF file, flipping the z-axis with the ORDER keyword;
  4) Regrid the variable (blindly, using @ASN) to depth coordinates.

I'm attaching a sample script to do this.

Before reaching this solution, I tried to invert the z-axis
when opening the original stream binary (step 1 above), which fails:

  yes? file/format=stream/var=v/grid=grid_abst/swap/order=y-z  mybin.dat
   **ERROR: command syntax: ORDER=Y-Z

This seems to mean that axis reversal isn't allowed for stream
datafiles.  (If so, the "command syntax" bit in the error message
is a little misleading because it suggests that "ORDER=Y-Z" is
syntactically incorrect.)

This was the reason why steps 2 & 3 were necessary.

Thanks, Steve.

Ryo

================================================================
!--- abstract grid ------------------------------------------
define axis/y=1:22:1  j_abst
define axis/z=1:101:1 k_abst
define grid/y=j_abst/z=k_abst grid_abst
!--- read the orginal stream binary and save to a netCDF ----
file/format=stream/var=v/grid=grid_abst/swap  mybin.dat
list/format=cdf/clobber/file=mybin-abst.nc v
cancel data/all

!--- real grid ----------------------------------------------
define axis/y=23.25S:12.75S:0.5             y_real
define axis/z=0:1000:10/units=meters/depth  z_real
define grid/y=y_real/z=z_real               grid_real
!--- read the netCDF file, inverting the z axis -------------
set data/order=y-z mybin-abst.nc
!--- regrid -------------------------------------------------
let new_v = v[g=grid_real@ASN]