[ncl-talk] Regridding data on unstructured grid with ESMF_Regrid
Peter Watson
watson at atm.ox.ac.uk
Mon Aug 25 11:06:26 MDT 2014
Thanks Mary. Trying that gave me a segmentation fault, though. When will
the next version of NCL be released?
Kind regards,
Peter
On Mon, Aug 25, 2014 at 5:58 PM, Mary Haley <haley at ucar.edu> wrote:
> Hi Peter,
>
> You may have run into a bug that we fixed in the upcoming release of
> NCL. I've attached a new "ESMF_regridding.ncl" script. Try saving it to
> the same directory as your script, and then comment out this line:
>
> load "$NCARG_ROOT/lib/ncarg/nclscripts/esmf/ESMF_regridding.ncl"
>
> and add this line after or before it:
>
> load "./ESMF_regridding.ncl"
>
> I'm not entirely sure this will work, because you may need to have the
> latest version of NCL to use this, but it's worth a try.
>
> --Mary
>
>
> On Mon, Aug 25, 2014 at 10:37 AM, Peter Watson <watson at atm.ox.ac.uk>
> wrote:
>
>> Thanks for your help Dennis. I tried this again, this time providing
>> the corner information as shown below, but got the same error message. My
>> input netCDF file regrid_cons_rg.nc (note I changed the filename) is now
>> structured as follows:
>>
>> netcdf regrid_cons_rg {
>> dimensions:
>> space = 35718 ;
>> corner = 4 ;
>>
>> variables:
>> double data(space) ;
>> double lon1d(space) ;
>> double lat1d(space) ;
>> double corner_lons(space, corner) ;
>> double corner_lats(space, corner) ;
>> }
>>
>> I added the corner_lons and corner_lats arrays, which define
>> tessellating rectangular cells centred on each grid point (except at the
>> northernmost and southernost latitudes, where the cells stretch to the
>> pole). I transferred the file regrid_cons_rg.nc by ftp as before.
>>
>> The following lines of ncl:
>>
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/esmf/ESMF_regridding.ncl"
>> file_in=addfile("regrid_cons_rg.nc","r")
>>
>> data = file_in->data
>> lats = file_in->lat1d
>> lons = file_in->lon1d
>> corner_lats = file_in->corner_lats
>> corner_lons = file_in->corner_lons
>>
>> Opt=True
>> Opt at SrcGridLat = lats
>> Opt at SrcGridLon = lons
>> Opt at SrcGridCornerLat = corner_lats
>> Opt at SrcGridCornerLon = corner_lons
>>
>> Opt at DstGridType = "5x5"
>> Opt at ForceOverwrite = True
>> Opt at InterpMethod="conserve"
>>
>> Opt at DstLLCorner = (/-85.0d, 0.0d /)
>> Opt at DstURCorner = (/ 85.0d, 355.0d /)
>>
>> Opt at Debug = True
>>
>> data_latlon=ESMF_regrid(data,Opt)
>>
>>
>> give the error:
>>
>> (0) ESMF_regrid_gen_weights: 'ESMF_RegridWeightGen' was successful.
>> (0) ESMF_regrid_with_weights: regridding using interpolation weights
>> ...
>> (0) ESMF_regrid_with_weights: warning: destination grid is not
>> (0) completely covered by the source grid. This is not an error.
>> (0) It just means your destination grid covers a larger area
>> (0) than your source grid.
>> (0) ESMF_regrid_with_weights: Source Grid:
>> (0) rank: 1
>> (0) dimensions: 71432
>> (0) original source rank: 1
>> (0) latitude min/max: -89.1415/89.1415
>> (0) longitude min/max:0.375/358.5
>> (0) ESMF_regrid_with_weights: Destination Grid:
>> (0) dimensions: 35 72
>> (0) latitude min/max: -85/85
>> (0) longitude min/max:0/355
>>
>> (0) ESMF_regrid_with_weights: retrieving interpolation weights ...
>> (0) ESMF_regrid_with_weights: error: source data on the description
>> (0) file does not have proper dimensions.
>>
>>
>> Is it possible to tell what is going wrong here? Or is there another
>> way of doing this?
>>
>> Kind regards,
>>
>> Peter
>>
>>
>> On Sat, Aug 23, 2014 at 3:28 AM, Dennis Shea <shea at ucar.edu> wrote:
>>
>>> The attached works with the bilinear and patch methods. The conserve
>>> method requires 'corner' information. NCL's implementation tries to derive
>>> the corner info but is not always successful. I think that is what is
>>> happening in your case. This will be looked at more when we get a chance.
>>>
>>>
>>>
>>>
>>> On Thu, Aug 21, 2014 at 1:52 PM, Peter Watson <watson at atm.ox.ac.uk>
>>> wrote:
>>>
>>>> Dear fellow NCL users,
>>>>
>>>> I am trying to do conservative regridding of precipitation data from a
>>>> reduced Gaussian grid to a lat-lon grid using the ESMF_Regrid function in
>>>> NCL 6.1.2, but I get an error that I do not understand. My input data is in
>>>> a NetCDF file, with the precip data and the latitudes and longitudes of the
>>>> grid points stored as 1D arrays. An ncdump -h of the input file gives:
>>>>
>>>> dimensions:
>>>> space = 35718 ;
>>>> variables:
>>>> double data(space) ;
>>>> double lon1d(space) ;
>>>> double lat1d(space) ;
>>>>
>>>>
>>>> I use the following lines of NCL, based on the example script at
>>>> http://www.ncl.ucar.edu/Applications/Templates/ESMF_unstruct_to_0.25deg.ncl
>>>> :
>>>>
>>>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
>>>> load "$NCARG_ROOT/lib/ncarg/nclscripts/esmf/ESMF_regridding.ncl"
>>>>
>>>> file_in=addfile("regrid_cons_irreg.nc","r")
>>>> data = file_in->data
>>>> lats = file_in->lat1d
>>>> lons = file_in->lon1d
>>>>
>>>> Opt=True
>>>> Opt at SrcGridLat = lats
>>>> Opt at SrcGridLon = lons
>>>> Opt at DstGridType = "5x5"
>>>> Opt at ForceOverwrite = True
>>>> Opt at InterpMethod = "conserve"
>>>> Opt at DstLLCorner = (/-85.0d, 0.0d /)
>>>> Opt at DstURCorner = (/ 85.0d, 355.0d /)
>>>>
>>>> Opt at Debug = True
>>>>
>>>> data_latlon=ESMF_regrid(data,Opt)
>>>>
>>>> This gives the error:
>>>>
>>>> (0) ESMF_regrid_with_weights: retrieving interpolation weights ...
>>>> (0) ESMF_regrid_with_weights: error: source data on the description
>>>> (0) file does not have proper dimensions.
>>>>
>>>> I don't understand why this fails. Is there something wrong with how I
>>>> am reading in the data and coordinates? Are there any conditions that need
>>>> to be satisfied, like the coordinates increasing monotonically (mine do
>>>> not)? If anyone has a script and NetCDF file for which this sort of
>>>> regridding succeeds that they could let me see, then that would be very
>>>> helpful.
>>>>
>>>> Thanks very much for any help you can give.
>>>>
>>>> Kind regards,
>>>>
>>>> Peter Watson
>>>>
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>>>>
>>>
>>
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