Re: [ferret_users] Interpolation 2D issue

[Szymon Roziewski <szymon.roziewski@xxxxxxxxx>]

Dear Martin / Ferreters,
I have problem with using fill_xy function. I saw some examples and read sth in the ferret archives but I still stuck.
I try to explain my issue.
This is reading an ice field and putting into a lndseaf. I also quote the grid definition.

DEFINE AXIS/X=-5.666666667:5.25:0.083333333/unit=degree xlon
DEFINE AXIS/Y=-2.0:10.0:0.083333333/unit=degree ylat
DEFINE GRID/x=xlon/y=ylat grid_xlon_xlat
file/skip=1/format=(80f1.0/52f1.0)/columns=132/grid=grid_xlon_xlat/var=lndseaf ICE.DAT

Then I interpolate the lndseaf onto a fine grid.

DEFINE AXIS/X=-5.666666667:5.25:0.010416667/unit=degree xfine
DEFINE AXIS/Y=-2.0:10.0:0.010416667/unit=degree yfine !1/8
DEFINE GRID/x=xfine/y=yfine grid_xfine_yfine
let ice_regridded lndseaf[gxy=grid_xfine_yfine]

What I did next was make the mask.

let mask = ice_regridded/ice_regridded

And I used the mask with fill_xy as the following 

let ice_ext = fill_xy(ice_regridded,mask,5)

But It didn't change anything. I tried out using different values of third argument of fill_xy. However, I didn't improve at all.
So, I think either I was using fill_xy badly or I misunderstood something.

I also tried out FLN function as follows

let ext = ice_regridded[x=@FLN:50,y=@FLN:50]

But this resulted with no changes to the ice_regridded as well.
I attach ICE.DAT to make it more real.

Kind regards,
Szymon Roziewski

2011/3/9 Martin Schmidt <martin.schmidt@xxxxxxxxxxxxxxxxx>

Dear Szymon,

you may use fill_xy(data, mask, 2) before you filter data. This extrapolates the data smoothly into land by two points and the filter @SBX and @SHN
can do something reasonable near land too. Applying your land mask later removes remaining extrapolated points.

Greetings,
Martin

Szymon Roziewski wrote:

Dear Ferreters,

I have an ice field that is a matrix filled by 0 or 1. Because of weak resolution I need it to be interpolated on a finer grid.
I tried out two approaches.
The first, I interpolated with using @SBX and @SHN functions. Basically, I got neat result except to the boundary where I got a lack of data. Because this functions don't have data to interpolate and ending up with 0 value.
As the second I used scat2gridgauss_xy function which gave me smoother result but near the boundary I got the ice that should not to be. I think that this function is do smooth the data sometimes to much.

Have any of you had something similar with it?
Maybe there are some good ferret functions to interpolate ice field which is 0 or 1.

I attach two graphics for better explanation.

Kind regards,
Szymon Roziewski

-- 
Z wyrazami szacunku,
Szymon Roziewski

Attachment: ICE.DAT.zip
Description: Zip archive