Re: Smoothing transformation and missing_value

[<hengkek@xxxxxxxxxx>]

Date: Tue, 04 Jun 2002 16:41:57 -0700
From: Steve Hankin <hankin@pmel.noaa.gov>
Organization: NOAA/Pacific Marine Environmental Laboratory
To: hengkek@nus.edu.sg

Hi Ansley,

fyi: the function
    MISSING(v[x=@sbx],v]
can be used to preserve the original values around the fringes.

    - s

=======

hengkek@nus.edu.sg wrote:

> Hi ferreters
>
> I'm trying to perform some smoothing transformation (provided by Ferret)
> on my gridded oceanographic data (to produce smoother contours) with
> unexpected results. The problem is, this transforms some originally
> valid datapoints to become "missing_value" points, namely around the
> land/ocean boundaries.  The "missing_value" in the original dataset is
> set to zero (0.0f) and denotes land.
>
> I took the easy way: I used the ferret gui and clicked on the buttons
> under "Transform" and tried all of the available schemes (boxcar,
> binomial, etc).  I modified the .jnl file to do the following:
>
> LET W_S = W_T[X=@SBN:3,Y=@SBN:3]
> use all3.nc  ! unsmooth dataset
> save/file=all_smooth.nc W_S
>
> It appears that the transformation is taking into account the grid
> points marked as "missing_value" in the original netCDF dataset.
>
> How do I prevent grid points marked as "missing_value" from being
> included in the transformations?
> Or how do I prevent originally valid data from being transformed into
> "missing_value" or "_Fillvalue"?
> Is there another way to smoothen my data without the above limitation?
> Is my use of zero for "missing_value" in the original dataset
> problematic?
>
> Thanks for any hints.
>
> -chk
> Physical Oceanography
> Singapore.

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