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Re: your mail : extracting data at given points
Hi Sudheer,
You can use SAMPLEXY function to sample a variable
at desired lat-lon locations. From the usermanual
(Ch3 Sec2.3.34. SAMPLEXY )
SAMPLEXY(DAT_TO_SAMPLE,XPTS,YPTS) Returns data sampled at a
set of (X,Y) points, using linear interpolation.
SAMPLEXY is a "grid-changing" function; its output grid is
different from the input arguments. Therefore it is best
to use explicit limits on the first argument rather than a
SET REGION command.
I think SAMPLEXY works well only for regular (equaly spaced)
X & Y axis (especially if the LONGITUDE axis is flagged as
MODULO). Anyway if you are planning to use Levitus Climatology
you don't have to worry about this.
Please have a look at the example given below.
Hope this helps
With Regards
Jaison
...........samplexy_lev.dat...........
LAT LON
=== ===
9.0 68.4
10.2 72.6
8.5 70.2
7.2 65.5
...............................
!---------samplexy_lev.jnl-----------
! open climatology dataset
set data levitus_climatology
! open ascii file containing lat-lon points
! use "/SKIP" to skip header lines if any
file/skip=2/var="lat,lon" samplexy_lev.dat
! do the sampling using SAMPLEXY function
let temp_lev = SAMPLEXY(temp[d=1], lon[d=2], lat[d=2])
list/k=1:5 temp_lev
! assign proper title and units if you are saving this to a file
set var/title="Temperature Extracted from Levitus Climatology"/\
units="^oC" temp_lev
set var/title="Latitude of data points"/units=latitudes lat
set var/title="Longitude of data points"/units=longitudes lon
sp rm -f samplexy_lev.nc
save/file=samplexy_lev.nc/append temp_lev
save/file=samplexy_lev.nc/append lon,lat
!-----------------------------------------------
On Tue, 23 Nov 2004, Sudheer Joseph wrote:
> Dear Users ,
> Is there any way to extract data from a netcdf file at
> specicifed( irregular) lat lon positions read from a file,
> essentially I needed the following
> file/var= lat,lon ll.dat
> get temperature data from levitus data.cdf @ lat log
>
> is there a method to get this data form the specified lat lon
> thanks,
> sudheer
>
> ***************************************
> Dr. Sudheer Joseph
> Indian National Centre for Ocean Information Services
> Gajularamaram B.O., IDA Jeedeemetla S.O.
> Via Pragathi Nagar, Kukatpally, Hyderabad
> Pin:5000 55
> Tel:+91-40-23044600(R)
> Tel:+91-40-9440832534(Mobile)
> Tel:+91-40-25503595(O)
> Fax:+91-40-25503596(O)
> E-mail:sjo@rediffmail.com;
> callsjo@yahoo.com;
> sjo@incois.gov.in.
> Web- http://oppamthadathil.tripod.com
> ***************************************
>
> _________________________________________________________________
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--
___________________________________________________
Jaison Kurian
Centre for Atmospheric and Oceanic Sciences
Indian Institute of Science
B A N G A L O R E 560 012
Ph: +91-80-3942505
+91-80-3600450
Fax:+91-80-3600865
___________________________________________________
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