[ncl-talk] extract_Data_from_polygon

[Guido Cioni]

Dear Kunal,
I didn’t answer to the first email because I am not really familiar with shapefile and masking over nations boundaries, but I guess there is a lot of documentation on the website. Is your a polygon just an approximation because you don’t know how to mask using the shape file or is it really what you wanted to do?

In order to extract the data you can either create a new variable where you mask the region outside of the polygon or where you put all the data inside of the polygon. I would use the first approach, since what you get is a variable with the same dimensions, but maybe the second one is easier. Since you have two arrays with lon,lat coordinates can’t you just create a new variable, called var2, which is a subset of var? 

Assuming that var has dimension (time, lat, lon) you can simply do that

var2=var(:,{lat},{lon})

The {} means that you are using coordinate indexing, it should work also with array although I’m not 100% sure. With this method you will get a variable with different dimensions. Otherwise you can try to mask using logical staments. Assuming you have (clon,clat) coordinates in your file (I used different names because of your definition in the script) you can try something similar

var2=mask(var, lon.ge.min(clon) .AND. lon.le.max(clon) .AND. lat.ge.min(clat) .AND. lat.le.max(clat), False)

Cheers


Guido Cioni
http://guidocioni.altervista.org <http://guidocioni.altervista.org/> 

> On 27 May 2016, at 12:31, Kunal Bali <kunal.bali9 at gmail.com> wrote:
> 
> Dear NCL
> 
> I tried to make the  polygon of the selected region. I don't know i did it correctly or not, please let me know is it correct way to do or not.
> 
> Second thig is that I need to extract the data from selected polygon. Could anyone please let me know how to do it ?
> 
> 
> Regards
> Kunal Bali
> 
> 
> 
> 
> 
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