Re: cssgrid does not ignore _FillValue

Travis,

Sorry for the multiple emails. This does appear to be a bug,
and it won't work if there are missing values in your longitude
data either. I think it's only going to work if your latitude
values contains missing values, so my kludge below should work
by forcing missing values into your latitude array.

I can give you a new binary with the fix, but I may not be able to get
to it right away.

--Mary

On Thu, 26 Jun 2008, Mary Haley wrote:

>
> Travis,
>
> I believe the documentation is misleading here. It does indeed claim
> "If missing values are detected in the input data, then those values
> are ignored when calculating the interpolating function."
>
> However, in looking at the code, it appears it is only applying to the
> lat/lon values, and not the actual data values.
>
> I'll check if this is a bug, or the intended behavior.
>
> Meanwhile, I think you can work around this in a kludgy fashion by
> setting one of your lat/lon arrays to missing values in the same
> locations that your input data is missing.
>
> For example, if "x" is your data array:
>
> lat@_FillValue = -9999 ; if not already set
> lat = where(ismissing(x), lat@_FillValue, lat)
>
>
> --Mary
>
>
> On Thu, 26 Jun 2008, Travis O'Brien wrote:
>
>> It appears that cssgrid_Wrap (and cssgrid) does not ignore missing values
>> (either @missing_value or @_FillValue) like the documentation says. I
>> discovered this when trying to interpolate station data (some of which are
>> missing data) using cssgrid.
>>
>> The bug can be replicated by modifying the example script from the cssgrid
>> documentation on the NCL website:
>> _________________________
>> ;**************************************************
>> ;************ Load necessary ncl code *************
>> ;**************************************************
>>
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl"
>>
>> begin
>>
>> ndata = 100
>> rlat = new(ndata,float)
>> rlon = new(ndata,float)
>> fval = new(ndata,float)
>>
>> ;
>> do i=0,ndata-1
>> rlat(i) = -90. + 180.*rand()/32767.
>> rlon(i) = -180. + 360.*rand()/32767.
>> end do
>> cartesian = css2c(rlat,rlon)
>> fval = cartesian(0,:)2 + cartesian(1,:)2 - 0.5*cartesian(2,:)2
>> fval@_FillValue = -1.0e20
>> fval(32) = -1.0e20
>>
>> printVarSummary(fval)
>>
>> ;
>> ; Set up the output grid.
>> ;
>> nx = 73
>> ny = 143
>> plat = 90.*fspan(-1.,1.,nx)
>> plon = 180.*fspan(-1.,1.,ny)
>>
>> ;
>> ; Calculate the interpolated function values.
>> ;
>> fint = cssgrid_Wrap(rlat,rlon,fval,plat,plon)
>>
>> print(avg(fint))
>>
>> end
>> _______________________________
>> Running ncl on this gives the following output:
>> Variable: fval
>> Type: float
>> Total Size: 400 bytes
>> 100 values
>> Number of Dimensions: 1
>> Dimensions and sizes: [100]
>> Coordinates:
>> Number Of Attributes: 1
>> _FillValue : -1e+20
>> (0) -7.442205e+17
>>
>> Running this script and omitting the line fval(32) = -1.0e20
>> gives a value for avg(fint) of about 0.2, versus the value given here of
>> about -1e17.
>>
>> NCL version:
>> 5.0.0
>> Output from uname -a:
>> Linux nimbus.pmc.ucsc.edu 2.6.9-55.0.2.ELsmp #1 SMP Tue Jun 26 14:14:47
>> EDT 2007 x86_64 x86_64 x86_64 GNU/Linux"
>>
>> and on another machine:
>>
>> NCL version:
>> 4.3.0
>> Output from uname -a:
>> Linux localhost.localdomain 2.6.25.4-10.fc8 #1 SMP Thu May 22 22:58:37 EDT
>> 2008 x86_64 x86_64 x86_64 GNU/Linux
>>
>> Thank you,
>> -Travis-
>>
>> --
>> Travis A. O'Brien
>> Graduate Student Researcher
>> Earth and Planetary Science Dept.
>> UC Santa Cruz
>>
>> tobrien_at_ucsc.edu
>> (831) 459-3504
>>
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>>
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Received on Thu Jun 26 2008 - 16:06:56 MDT