Re: [ferret_users] PT_IN_POLY

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

Hi Anja,
Thank you for writing.  You are right, the function does not apply a 
modulo operation to translate longitudes if they don't match the 
longitude range in the grid of the variable.  Also, the grid of the 
etopo datasets are perhaps unexpected in that the longitudes run from 20 
to 380 instead of 0 to 360.

I'll put a note in the documentation about this, and we should be able 
to improve the function itself so that it would do that translation.

Ansley

On 9/5/2012 12:01 AM, Anja Eggert wrote:
> Dear Ferret developers,
> I just noticed a problem when I used the function PT_IN_POLY and the 
> choice of the region. First I used the example from the ferret site. 
> It worked and I wanted to run my own example in the Benguela upwelling 
> area off Namibia at approx. 10°E-14°E.
>
>
> This is my example that does not work:
>
> use etopo60
> let xp = {10.1,10.4,10.3,11.6,14,11.5,10.1}
> let yp = {-17,-19,-20,-23,-23,-17,-17}
> go basemap x=-20:50 y=10:-40 20
> plot/vs/thick/line/color=blue/over/nolab xp,yp
> let mask = if pt_in_poly(rose,xp, yp) gt 0 then 1
> shade /over mask
>
>
> This is my example that does work:
>
> use etopo60
> let xp = {370.1,370.4,370.3,371.6,374,371.5,370.1}
> let yp = {-17,-19,-20,-23,-23,-17,-17}
> go basemap x=340:410 y=10:-40 20
> plot/vs/thick/line/color=blue/over/nolab xp,yp
> let mask = if pt_in_poly(rose,xp, yp) gt 0 then 1
> shade /over mask
>
> Okay, I know now what I need to do. But it was very confusing for 
> several hours.... So maybe this problem is worth to get your attention?
>
> Cheers,
> Anja