Re: [ferret_users] choosing a grid point

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi -
Aha. This form of data, with longitude and latitude as 2D coordinate 
variables, is what Ferret calls "curvilinear" data. The X and Y axes are 
just index values (usually) in such a dataset, and the coordinate 
information is all in the variables LON and LAT. For 2D plots in x and 
y, you can use the curvilinear form of the plot commands, such as

yes? fill/L=500 zo, lon, lat

To plot a line from this kind of data we need to sample at the longitude 
latitude point we want to use:

yes? PLOT SAMPLEXY_CURV(zo[L=1:600], lon, lat, 359, 54)

The above will find the location at each time given, L=1:600.  The 
values in the last two arguments to the function must be within the 
range of the variables LON and LAT; depending on how these are given in 
the file you might need to use a different modulo replication of 359.  
SHADE LON and SHADE LAT are useful ways to see how LON and LAT look, or 
STAT LON and STAT LAT to give summary statistics of them.

If in fact the data are on a rectangular grid, we can use the 
information in LON and LAT to create longitude and latitude axes, put 
the variable zo on those axes, and then use the full range of Ferret 
commands to do subsetting and graphics and so on. Let us know if that's 
the case and we can help.

Ansley

Anup Sherchan wrote:
> Dear ferret users
>          Thanks to all who replied but my problem still exists. I'm 
> trying to create a harmonic analysis of tides. I chose some 
> coordinates say California, England (1W, 54N ), Philippines and I want 
> to have the plot of sea level [depth in meter] wrt time [days]. I can 
> do so by choosing the location using ncview as seeing what the 
> corresponding values of i and j at that position might be, but I want 
> the exact coordinates, as 1 W, 54 N for Immingham, England.
>
> /http://lpas.epfl.ch/MOD/manuals/ferret/chapter4.html/
>
> /yes? SET DATA levitus_climatology
> yes? SET REGION/X=180/Y=0                      ! true profile
> yes? PLOT/Z=0:5000 temp
> yes? DEFINE AXIS/DEPTH/Z=100:2000:100  zfalse
> yes? DEFINE GRID/LIKE=temp/Z=zfalse  gfalse    ! false profile
> yes? PLOT/Z=0:5000/OVERtemp[G=gfalse@ASN] /
>
> The above mentioned weblink shows some similarity but doesn't work in 
> my case, when I execute the first 3 lines as shown above, gives me the 
> following error
>
> /yes? show data/full
>     currently SET data sets:
>    1> ./ZETA.nc  (default)
>
> name     title                             I         J         
> K         L
> LON      longitude                        1:120     1:101     
> ...       ...
>             degrees on grid GIH1 with -1.000000E+34 for missing data
>             X=0.5:120.5  Y=0.5:101.5
> LON_BOUNDS
>                                           1:4       1:120     
> 1:101     ...
>               on grid GIH2 with -1.000000E+34 for missing data
>             X=0.5:4.5  Y=0.5:120.5  Z=0.5:101.5
> LAT      latitude                         1:120     1:101     
> ...       ...
>             degrees on grid GIH1 with -1.000000E+34 for missing data
>             X=0.5:120.5  Y=0.5:101.5
> LAT_BOUNDS
>                                           1:4       1:120     
> 1:101     ...
>               on grid GIH2 with -1.000000E+34 for missing data
>             X=0.5:4.5  Y=0.5:120.5  Z=0.5:101.5
> TIME                                      ...       ...       
> ...       1:8760
>       (invalid coordinate axis)
>             day as %Y%m%d.%f on grid GIH3 with -1.000000E+34 for 
> missing data
>
> ZO       sealevel                         1:120     1:101     
> ...       1:8760
>             m on grid GIH4 with -1.000000E+34 for missing data
>             X=0.5:120.5  Y=0.5:101.5
>
>  time range: 1 to 8760/
> /yes? plot zo[l=1:8760]
> **ERROR: dimensions improperly specified: specified data is not a line
>           - its a 3D region: "plot zo[l=1:8760]"
> yes? set region/x=1W/y=54N
> yes? plot/l=1:8760 zo
> **ERROR: illegal limits: "ZO" is not in the range X=359
>          Axis extremes are X=0.5:120.5
> /
> Help needed. Thanks.
>
> Anup Sherchan

--

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Ansley Manke, NOAA/PMEL   ansley.b.manke@xxxxxxxx
7600 Sand Point Way NE, Seattle WA
Phone 206-526-6246,  FAX 206-526-6744