[gradsusr] Help on calculating Area Maximum from NetCDF file using Grads

[Arlindo da Silva]

On Mon, Jun 30, 2014 at 9:37 AM, Anil Kumar <anilku at oceanmanager.com> wrote:

> Hi Grads users,
>
>
>
> I am awaiting an useful comments or direction on the below case. Please
> lead me, to get all the maximum values from the small – small areas of
> every 2 degree in Lat and lon say for example. Below is my complete query.
>
>
>
> *My Requirement* :  I have a larger dataset (.NC file) 1440*720 points. I
> want a new destination grid with linear interpolation having all the all
> area maximum values using amax() of small-small regions. And ultimately,
> need to query the destination grid for output.
>
>
>

I am afraid the regridding method you are looking for is not implemented by
lterp() or re().  This is a good example of when GrADS is not the best tool
for the job at hand. But if you insist, a very inefficient approach would be

1) define a 2x2 global grid (say, use lterp with linear interpolation),
2) loop over every 2x2 region in the 0.25x0.5 deg grid, compute the 2 x2
area max with amax(), and use "set defval" to replace the corresponding
value in the previous defined variable in 1). As I said, this is very
inefficient.

If you are up for some C/Fortran programming, you can use the opengrads IPC
extension (which is available with your Windows build):

    http://opengrads.org/doc/udxt/libipc/

to write your variables to disk,

ga-> ipc_save u_velocity u.bin
ga-> ipc_save v_velocity v.bin

Then write a C/Fortran program that read these files (u.bin,v.bin) and
compute the amax at the 2x2 grid you require, writing output files
(u2x2.bin.v2x2.bin).

ga-> ! my_amaxregrid

Consult the IPC documentation for the description of the transfer file
format (very similar to the old GrADS 1.x UDF.) You can finally read these
back with ipc_load() extension:

ga-> d ipc_load("u2x2.bin");ipc_load("v2x2.bin")

Notice that this is a poor-man version of the file-based UDF that existed
in GrADS 1.x. Of course, you can accomplish the same more efficiently by
writing a genuine OpenGrADS extension with no transfer files involved.

  Good Luck,

      Arlindo





> *What Am doing so far : *
>
> I have a NetCDF file having  below CTL Info.
>
>
>
> *****************************************************************
>
> dset D:\WeatherGribFiles\2014\06\22\rtofs_glo_2ds_f024_daily_prog.nc
>
> title 2D Sfc Daily Prognostic 00Z22jun2014: Forecast, downloaded Jun 22
> 15:20 UTC
>
> undef 1.26765e+30
>
> dtype netcdf
>
> xdef 1440 linear 74.16 0.24999
>
> ydef 720 linear -90 0.24999
>
> zdef 1 linear 1 1
>
> tdef 1 linear 00Z23JUN2014 1mn
>
> vars 2
>
> u_velocity=>u_velocity  1  t,z,y,x  eastward_sea_water_velocity (m/s)
>
> v_velocity=>v_velocity  1  t,z,y,x  northward_sea_water_velocity (m/s)
>
> endvars
>
> *****************************************************************
>
>
>
> I want a new destination grid ; which would contain the area maximum
> values as points. Destination grid should contain maximum value from every
> 8 points in x-axis and y axis. For this, I have created below, CTL file
> named as  *rtofs_glo_2ds_f024_daily_prog.ctl*:
>
>
>
> *****************************************************************
>
> dset D:\WeatherGribFiles\2014\06\22\rtofs_glo_2ds_f024_daily_prog.nc
>
> index  D:\WeatherGribFiles\2014\06\22\rtofs_glo_2ds_f024_daily_prog_DUMMY.nc
>
>
> title 2D Sfc Daily Prognostic 00Z22jun2014: Forecast, downloaded Jun 22
> 15:20 UTC
>
> undef 1.26765e+30
>
> dtype netcdf
>
> xdef 180 linear 74.16 2.0
>
> ydef 90 linear -90 2.0
>
> zdef 1 linear 1 1
>
> tdef 1 linear 00Z23JUN2014 1mn
>
> options template
>
> vars 2
>
> u_velocity=>u_velocity  1  t,z,y,x  eastward_sea_water_velocity (m/s)
>
> v_velocity=>v_velocity  1  t,z,y,x  northward_sea_water_velocity (m/s)
>
> endvars
>
> *****************************************************************
>
> Below is the command I use to display the data from destination grid *rtofs_glo_2ds_f024_daily_prog_DUMMY.nc
> *defined in above CTL file. Below is the command set using.
>
>
>
> *****************************************************************
>
> reinit
>
> sdfopen D:/WeatherGribFiles/2014/06/22/rtofs_glo_2ds_f024_daily_prog.nc
>
> open D:/WeatherGribFiles/2014/06/22/rtofs_glo_2ds_f024_daily_prog2.ctl
>
> set parea 0 11 0 8.5
>
> set vpage 0 11 0 8.5
>
> set lon -74.16 434
>
> set lat -90 90
>
> set cthick 6
>
> set arrscl 0.10
>
> define val =
> mag(lterp(u_velocity.1*1.95,lat.2,amax),lterp(v_velocity.1*1.95,lat.2,amax))
>
> d
> lterp(u_velocity.1*1.95,lat.2,amax);lterp(v_velocity.1*1.95,lat.2,amax);val
>
>
>
> *****************************************************************
>
>
>
> When I change the destination grid dimensions slightly  in *rtofs_glo_2ds_f024_daily_prog.ctl
> *file
>
>
>
> xdef 135 linear 74.16 2.5
>
> ydef 68 linear -90 2.5
>
>
>
> and checks for the output, It varies at the same point i.e. if I look at
> certain point before changing and after changing grid dimensions, the
> result comes of different magnitude.
>
> What I want is, When I increase or decrease the destination grid points in
> “*rtofs_glo_2ds_f024_daily_prog.ctl”, *and the maximum value should be at
> its place.
>
>
>
> How can I achieve this ?????
>
>
>
>
>
> *Thanks & Regards*
>
> *Anil Kumar – **Sr. **Software Developer*
>
> *OceanManager* *Inc.* | www.oceanmanager.com
>
> Tel: + 91-172-5026090, 5026091, 4646070
>
> *OceanManager- Marine Software*
>
>
>
> *From:* gradsusr-bounces at gradsusr.org [mailto:
> gradsusr-bounces at gradsusr.org] *On Behalf Of *Anil Kumar
> *Sent:* Friday, June 27, 2014 12:55 PM
> *To:* jma at cola.iges.org; 'GrADS Users Forum'
> *Subject:* Re: [gradsusr] Help on calculating Area Maximum from NetCDF
> file using Grads
>
>
>
> Hi Jennifer and All,
>
>
>
> Am seeking help on calculating area maximum with linear interpolation
> using Grads. Earlier I was using below methodology to calculate area
> average over small areas defined. It was working good but now I need to
> calculate amax using lterp in grads but in documentation I cannot find
> that ltrep uses amax as argument
> <http://www.iges.org/grads/gadoc/gradfunclterp.html> ; neither it is
> giving correct result nor giving error.
>
>
>
> *My Requirement* :  I have a larger dataset (.NC file) 1440*720 points. I
> want a new destination grid with linear interpolation having all the all
> area maximum values using amax() of small-small regions. And ultimately,
> need to query the destination grid for output.
>
>
>
> *What Am doing so far : *
>
> I have a NetCDF file having  below CTL Info.
>
>
>
> *****************************************************************
>
> dset D:\WeatherGribFiles\2014\06\22\rtofs_glo_2ds_f024_daily_prog.nc
>
> title 2D Sfc Daily Prognostic 00Z22jun2014: Forecast, downloaded Jun 22
> 15:20 UTC
>
> undef 1.26765e+30
>
> dtype netcdf
>
> xdef 1440 linear 74.16 0.24999
>
> ydef 720 linear -90 0.24999
>
> zdef 1 linear 1 1
>
> tdef 1 linear 00Z23JUN2014 1mn
>
> vars 2
>
> u_velocity=>u_velocity  1  t,z,y,x  eastward_sea_water_velocity (m/s)
>
> v_velocity=>v_velocity  1  t,z,y,x  northward_sea_water_velocity (m/s)
>
> endvars
>
> *****************************************************************
>
>
>
> I want a new destination grid ; which would contain the area maximum
> values as points. Destination grid should contain maximum value from every
> 8 points in x-axis and y axis. For this, I have created below, CTL file
> named as  *rtofs_glo_2ds_f024_daily_prog.ctl*:
>
>
>
> *****************************************************************
>
> dset D:\WeatherGribFiles\2014\06\22\rtofs_glo_2ds_f024_daily_prog.nc
>
> index  D:\WeatherGribFiles\2014\06\22\rtofs_glo_2ds_f024_daily_prog_DUMMY.nc
>
>
> title 2D Sfc Daily Prognostic 00Z22jun2014: Forecast, downloaded Jun 22
> 15:20 UTC
>
> undef 1.26765e+30
>
> dtype netcdf
>
> xdef 180 linear 74.16 2.0
>
> ydef 90 linear -90 2.0
>
> zdef 1 linear 1 1
>
> tdef 1 linear 00Z23JUN2014 1mn
>
> options template
>
> vars 2
>
> u_velocity=>u_velocity  1  t,z,y,x  eastward_sea_water_velocity (m/s)
>
> v_velocity=>v_velocity  1  t,z,y,x  northward_sea_water_velocity (m/s)
>
> endvars
>
> *****************************************************************
>
> Below is the command I use to display the data from destination grid *rtofs_glo_2ds_f024_daily_prog_DUMMY.nc
> *defined in above CTL file. Below is the command set using.
>
>
>
> *****************************************************************
>
> reinit
>
> sdfopen D:/WeatherGribFiles/2014/06/22/rtofs_glo_2ds_f024_daily_prog.nc
>
> open D:/WeatherGribFiles/2014/06/22/rtofs_glo_2ds_f024_daily_prog2.ctl
>
> set parea 0 11 0 8.5
>
> set vpage 0 11 0 8.5
>
> set lon -74.16 434
>
> set lat -90 90
>
> set cthick 6
>
> set arrscl 0.10
>
> define val =
> mag(lterp(u_velocity.1*1.95,lat.2,amax),lterp(v_velocity.1*1.95,lat.2,amax))
>
> d
> lterp(u_velocity.1*1.95,lat.2,amax);lterp(v_velocity.1*1.95,lat.2,amax);val
>
>
>
> *****************************************************************
>
>
>
> When I change the destination grid dimensions slightly  in *rtofs_glo_2ds_f024_daily_prog.ctl
> *file
>
>
>
> xdef 135 linear 74.16 2.5
>
> ydef 68 linear -90 2.5
>
>
>
> and checks for the output, It varies at the same point i.e. if I look at
> certain point before changing and after changing grid dimensions, the
> result comes of different magnitude.
>
> What I want is, When I increase or decrease the destination grid points in
> “*rtofs_glo_2ds_f024_daily_prog.ctl”, *and the maximum value should be at
> its place.
>
>
>
> How can I achieve this ?????
>
>
>
> Thanks for any guidance.
>
>
>
> *Thanks & Regards*
>
> *Anil Kumar*
>
> _______________________________________________
> gradsusr mailing list
> gradsusr at gradsusr.org
> http://gradsusr.org/mailman/listinfo/gradsusr
>
>


-- 
Arlindo da Silva
*dasilva at alum.mit.edu <dasilva at alum.mit.edu>*
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