Re: [ferret_users] Question about regridding

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi Ming,
I suspect that the longitude axes here are not defined as  MODULO axes, 
which would tell Ferret to wrap the points around the earth. (If you say 
"SHOW GRID topo", a modulo X axis would have an m after the number of 
points in X). The important one is the axis of the topo dataset which 
you want to wrap around from 0.5 across 0 to 359.5. You can give the 
axis a modulo setting by saying

  yes? use atmym016910.t2m.nc
  yes? use topo.nc
  yes? set axis/modulo `topo,return=xaxis`
  yes? let TOPO2=TOPO[G=T2M[d=1]]


and then the regridding should proceed as you want it to.

Ansley


Ming Yang wrote:

> Hi, folks
>    Here is my original dataset
>
> topo.nc
> LON = 0.5, 1.5, ..., 359.5
> LAT = -89.5, -88.5, ..., 89.5
>
>    I want this dataset to be regridded so that it shares the same
> coordinates as the following dataset
>
> atmym016910.t2m.nc
> LON = 0, 5.625, ..., 354.375
> LAT = -85.76059, -80.26878, ..., 80.26878, 85.76059
>
>    Here is what I have done with ferret
>
> yes? use atmym016910.t2m.nc
> yes? use topo.nc
> yes? show data
>     currently SET data sets:
>    1> ./atmym016910.t2m.nc
> name     title                             I         J         K
> L
> T2M      Temperature at 2 Meter           1:64      1:32      ...
> 1:500
>
>    2> ./topo.nc  (default)
> name     title                             I         J         K
> L
> TOPO     TOPO                             1:360     1:180     ...
> ...
>
> yes? let TOPO2=TOPO[G=T2M[d=1]]
>
>     TOPO2 has the desired coordinate, the same as T2M. However, I notice
> in TOPO2 the values for LON=0 are undefined. I think this is because
> the LON=0 is outside the range of the orignial dataset, whose lon is from
> 0.5 to 359.5, and the ferret is not smart enough to wrap up the longitude
> around and to make use of those values with LON=359.5. Does anyone know
> how to fix this problem? Thank you in advance.
>
>
> Best,
> Ming
>
>
>