Re: [ferret_users] polygon to mask country

[Nicolas Freychet <nicolas.freychet@xxxxxxxxx>]

Hi Ansley,

Yes it does show the right boundary. Actually I found a solution by specifying the i/j limits of the var in the definition (I think because I used "dimensional" lists to define the polygon, it was somehow inconsistent with dimension of the variable). So something like that works:

let xp=LON[d=7,i=1:735178]

let yp=LAT[d=7,i=1:735178]

let mask = if pt_in_poly(Tmax[d=1,l=1,i=1:350,j=1:95],xp,yp) gt 0 then 1

Cheers,

Nicolas

Le mar. 26 mars 2019 à 16:22, Ansley C. Manke <ansley.b.manke@xxxxxxxx> a écrit :

Hi Nicolas,

As a check of your definition, does a plot of the points

   PLOT/VS/LINE xp, yp

show the outline of the boundary you want?

On 3/25/2019 4:18 AM, Nicolas Freychet wrote:
> Dear Ferret users,
>
> I'm trying to create a mask for a country, following this discussion:
> https://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2012/msg00019.html
>
> I managed to have a netcdf file with all lon/lat coordinate to define
> a polygon of the country as in the discussion, but now I am not sure
> how to apply it to mask my data.
> The pt_in_poly function
> (https://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/appendix-a-external-functions/pt_in_poly)
> requires to define a table of xp/yp. I tried to do something like:
>
> let xp=LON[d=7,i=1:735178]
> let yp=LAT[d=7,i=1:735178]
> let mask = if pt_in_poly(Tmax[d=1,l=1],xp,yp) gt 0 then 1
>
> But it doesn't seem to work. I think it's the way I define xp/yp that
> is wrong, but I don't know how to make a table {} from a coordinate.
> Any idea?
>
> Cheers,
> Nico
>

--

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Nicolas Freychet

PDRA, School of Geosciences
University of Edinburgh
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