Re: [ferret_users] FILL w/o interpolation at coast line?

[Martin Schmidt <martin.schmidt@xxxxxxxxxxxxxxxxx>]

Hi Steve,

guess your problem is, that you have zero and not missing values in your 
land points? Then you may want to replace such data with missing values 
before you
make a plot. Possibly this helps.

Another hint - there is a function fill_xy, which extrapolates data as 
smooth as possible. It fills missing values with average values from 
valid neighbour points.
It is of some help, if you want to interpolate and extrapolate data and 
have some of your interpolation grid points near land.

use coads_climatology
fill/l=10 sst[d=1]
SET MEMORY/SIZE=100
go fland 5

You will see some white areas near land.

Now define a field of ones, needed for fill_xy

let mask=0*missing(sst[l=1],1)+1
let sst_fill=fill_xy(sst,mask,2)

fill_xy fills missings, if the mask is 1 and does nothing, if mask is 0. 
"2" is the number of
nearest neighbour filling cycles.

Enhancing this value defines SST also around Antarctica. So be carefull.

set win 2
fill/l=10 sst_fill[d=1]
go fland 5

If you have zeros at land, you may proceed in two steps. First replace 
zeros by missings. Then you
may extrapolate as described here.

Please note, a nearest neighbour filler does about the same here. But 
again, first you should
replace zeros (valid data) with missing values.

Does this solve your problem?

Best,
Martin