[ncl-talk] extract_Data_from_polygon

[Guido Cioni]

Dear Kunal,
attached you find the resulting script. First I subsetted the var over the domain that you specified (the one that is used to plot the polygon) and obtain var2. Then I did some trick to get the lat/lon coordinates printed in the CSV file. 




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




> Il giorno 27 mag 2016, alle ore 17:51, Kunal Bali <kunal.bali9 at gmail.com> ha scritto:
> 
> I am not getting it exactly how to do this one. 
> Could any one please help me out to do this. 
> 
> Kunal Bali
> Research Scholar 
> Radio & Atmospheric Science Division 
> CSIR - National Physical Laboratory
> New Delhi - 110012
> India
> 
> 
> 
> 
> 
> On Fri, May 27, 2016 at 6:12 PM, Guido Cioni <guidocioni at gmail.com <mailto:guidocioni at gmail.com>> wrote:
> Once you have the correct variable you can write it to an CSV file by using the write table function.
> 
>  alist=[/clon,clat,var2/]
>  write_table(“file.csv”,"w",alist,”%f,%f,%f,%f")
> 
> Guido Cioni
> http://guidocioni.altervista.org <http://guidocioni.altervista.org/> 
> 
>> On 27 May 2016, at 14:24, Kunal Bali <kunal.bali9 at gmail.com <mailto:kunal.bali9 at gmail.com>> wrote:
>> 
>> Dear Guido
>> 
>> Thanks for the information. 
>> Actually, I need to extract the data as ASCII or CSV file of the selected polygon box
>> 
>> 
>> 
>> Kunal Bali
>> Research Scholar 
>> Radio & Atmospheric Science Division 
>> CSIR - National Physical Laboratory
>> New Delhi - 110012
>> India
>> 
>> 
>> 
>> 
>> 
>> On Fri, May 27, 2016 at 5:35 PM, Guido Cioni <guidocioni at gmail.com <mailto:guidocioni at gmail.com>> wrote:
>> 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 <mailto: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
>>> 
>>> 
>>> 
>>> 
>>> 
>>> <polygon.ncl><polygon.png>_______________________________________________
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>> 
>> 
> 
> 
> <FRP.nc>

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