Re: [ferret_users] Visualizing GEBCO with Ferret

[Martin Schmidt <martin.schmidt@xxxxxxxxxxxxxxxxx>]

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)
SET MEMORY/SIZE=500
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 ....
SET MEMORY/SIZE=500
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

or

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,
Martin


Tim Loomis wrote:

> All,
> 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