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Re: [ferret_users] Visualizing GEBCO with Ferret

Hi Tim, Ansley and Ned,

many thanks for your suggestions. I was not aware of the npoints specifier.

The GEBCO - topography is available in the web, but not at an OPeNDAP-Server. Just visit http://www.gebco.net/. You will have to register there. Data are available with a manual. For my example I have the number of points and the grid spacing. From this it is clear that the coordinates must be edges. But you are right, this needs to be verified.

Tim, I will send you a script to read and visualise data Thursday. For me it is late in the evening and tomorrow I am away. If you need it today, please try the following:

- download your data segments, the full set is huge!
- use nco-tools (ncrename) to change the name of data in the file from z to za (please use the man page). I did not find another solution.

  ncrename -v z,za   your_file_name

- use ncdump to find the numer of grid points to be used with the npoints specifier to get your axes

  ncdump your_file | less

- modifiy the following script for your purposes. Use your coordinates and you may want to use the npoints specifier as proposed by Ansley and Ned in their letters.

use "20n50s60w50e_GEBCO_08.nc"
define axis/x=`X_RANGE[i=1]`:`X_RANGE[i=2]`:`0.0083334`/edges /units="degrees_east" xax define axis/y=`Y_RANGE[i=1]`:`Y_RANGE[i=2]`:`0.0083334`/edges /units="degrees_north" yax
define grid/x=xax/y=yax xygrid
let dummy=0*x[gx=xygrid]+0*y[gy=xygrid]
!reshape data that are stored 1D to a 2D field, dummy has the correct dimension and the right axes
let depth=reshape(za,dummy)
save/file=zw.nc/clobber depth
can data/all
can var depth
can grid xygrid

! Now we need to flip the axis. Possibly this can be done in connection with the data reading step ....
use/order=X-Y zw.nc
let/unit=m/title="gebco topography" topo=depth
save/file=depth_20n50s60w50e_GEBCO_08.nc/clobber topo

There may be better solutions ...

Now you can use ferret to make plots or use shade and fill. Please be aware that the data set may be huge and do not plot much more points than needed.

use your file
set region/x=xl:xh/y=yl:yh
shade/lev=   your levels  topo


use your file
shade/lev=   your levels  topo[i=1:10000:100,j=1:5000:20]

Please see the ferret doc for more details.

Good luck,

Tim Loomis wrote:

I'm new to Ferret and would like to find someone who has used it to access the gebco_08.nc. I need some high resolution images out of it. Any help would be appreciated. Any tutorials out there?....Tim

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