Re: radius and cutoff values in scat2gridgauss_xy command

[Billy Kessler <William.S.Kessler@xxxxxxxx>]

Hello Yogesh -

First, I'm not exactly sure what you mean by "radius" in your
example, since there is no such argument to the SCAT2GRIDGAUSS*
functions.

But I assume that you mean the arguments XSCALE and YSCALE,
which control the width of the Gaussian function used to do
the mapping.

However, there is no direct way to implement your rule:
SCAT2GRIDGAUSS will fill any gridbox that has the weight
function

W_n(x_n,y_n) = exp{-[(x_n-x_0)/XSCALE]^2 - [(y_n-y_0)/YSCALE]^2}

greater than exp{-CUTOFF^2}. (See note re CUTOFF at bottom).

In general, this will "spread" the observations over gridpoints
that had no obs to begin with.

We are implementing an additional external function that will
count the number of obs/gridbox. If you need to get your answer
today, then you could think about how to make a mask for your
grid based on the number of obs in each gridbox, and use that
to blank out gridpoints you don't want.

Note re CUTOFF: CUTOFF should be a single number, not separate
numbers for the x and y axes. This was a mistake when the fortran
code was implemented as an external function. It will be fixed in
a future release. IN the meantime, please use the same value for
XCUTOFF and YCUTOFF. A good value is 2, which means that data points
far enough away from the gridpoints so that the value of the weight 
function is less than exp{-4} = 0.018 will not be used in the calculation
for that gridpoint. This will exclude data values more than twice the
scale distances from each gridpoint. 

Billy K


> Date: Mon, 07 Feb 2005 12:44:10 +0100
> From: "Yogesh K. Tiwari" <ktiwari@bgc-jena.mpg.de>
> To: ferret_users <oar.pmel.ferret_users@noaa.gov>
> Subject: radius and cutoff values in  scat2gridgauss_xy  command
> 
> Hello Ferret Users,
> 
> I could not understand exactly the meaning of cutoff
> and radius values in the scat2gridgauss*  ferret command.
> 
> I want to make a rule while griding my scattered data as,
> 
> I required that there are at least 10 observations
> in a grid box 1x1 while using the scat2gridgauss_xy command.
> 
> Whether my following radius and cutoff values are right for my
> above rule (10 obs in a grid).
> 
> 
>       define symbol radius = 0.25
>       define symbol cutoff = 2.0
> 
> Many many thanks in advance for your help.
> 
> Regards,
> Yogesh
> 
> -- 
> 
> ===========================================
> Yogesh K. Tiwari,
> Max-Planck Institute for Biogeochemistry,
> Beutenberg Campus, Hans-Knoell-Strasse 10,
> D-07745 Jena,
> Germany
> 
> Office   : 0049 3641 576376
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> e-mail   : yogesh.tiwari@bgc-jena.mpg.de
> ===========================================
> 
>