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Re: [ferret_users] Visualizing GEBCO with Ferret

Hi Tim,

here my final version, how to deal with GEBCO-topography files:

1. Unfortunately the name of the depth field is "z". This name is used by ferret for axes. I did not find a ferret-solution, you have to rename it using nco-tools. It is easy, if nco-tools are installed. Otherwise I recommend to do so, they are very useful.

ncrename -v z,za  your-file

2. Ferret prefers a different way to have axes and data defined and linked with each other. Hence, you have to reformat the data. The data format in the files you may download are for other tools described at the web-pages.

I am not sure about the following!!! I read the manual, but could not find some statement, where grid points are exactly defined. So I downloaded a 1 deg x 1 deg rectangle and got 61 coordinate points for the "1min"-topography and 120 points for the"08" highly resolving data set respectively.
- in the 1 deg file the coordinates are cell edges
- in the 0.5 deg file the coordinates are cell mid points

Please inspect your file with ncdump to be sure, that your final grid after reformatting the data has the same size.

Write a script map_to_axes.jnl. For sure there are mor elegant solutions.
use "$1"
define axis/x=`X_RANGE[i=1]`:`X_RANGE[i=2]`/npoints=`dimension[i=1]`/edges /units="degrees_east" xax define axis/y=`Y_RANGE[i=1]`:`Y_RANGE[i=2]`/npoints=`dimension[i=2]`/edges /units="degrees_north" yax !Please remove the edges - specification, if you read highly resolved topography files.!!!!!!!!!!!!!!!!!!!!!
define grid/x=xax/y=yax xygrid
let dummy=0*x[gx=xygrid]+0*y[gy=xygrid]
let depth=reshape(za,dummy)
save/file=zw.nc/clobber depth
can data/all
can var depth
can grid xygrid

! Now flip the y-axis. Read data again and write to a new file.
use/order=X-Y zw.nc
let/unit=m/title="gebco topography" topo=depth
save/file=depth_$1/clobber topo

Now you can use ferret to make plots.
use depth_your-filename
shade topo

I recommend, not to use the full data sets with the shade command. It is huge and the plot - resolution is not fine enough for the details.
Otherwise please read the manual.
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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