# Re: [ferret_users] choosing a grid point

```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

```
```
--

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

```