Re: [ferret_users] interpolation

[David Wang <climater@xxxxxxxxx>]

Thanks a lot, Ansley.

Now I'm aware that it is Ferret, not the dataset itself, that sets cell 
edges at midpoints between grid points. So if I understand it correctly, 
linear interpolation through regridding has nothing to do with the 
position of cell edges, it simply takes two adjacent grid points and 
calculates the linear combination at the target point in between, 
doesn't it?

- D.W.

Ansley Manke wrote:

> Hi David,
> By default Ferret assumes that cell edges are midway between grid 
> points, in the absence of other information. Using the concept of cell 
> boundaries/edges one can define the axis in whichever way you like, 
> however in this case it seems that Ferret's definition of the cells on 
> the axis is the one you already want:
>
> yes? use levitus_climatology
>
> yes? let zz = z[gz=temp]
> yes? let zlo = zboxlo[gz=temp]
> yes? let zhi = zboxhi[gz=temp]
>
> yes? list zz, zlo, zhi, zz-zlo, zhi-zz
>             DATA SET: 
> /home/porter/tmap/fer_dsets/data/levitus_climatology.cdf
>             DEPTH (m): 0 to 5000
> Column  1: ZZ is Z[GZ=TEMP]
> Column  2: ZLO is ZBOXLO[GZ=TEMP]
> Column  3: ZHI is ZBOXHI[GZ=TEMP]
> Column  4: EX#4 is ZZ-ZLO
> Column  5: EX#5 is ZHI-ZZ
>
>                 ZZ    ZLO    ZHI   EX#4   EX#5
> 0       /  1:     0.     0.     5.    0.0    5.0
> 10      /  2:    10.     5.    15.    5.0    5.0
> 20      /  3:    20.    15.    25.    5.0    5.0
> 30      /  4:    30.    25.    40.    5.0   10.0
> 50      /  5:    50.    40.    62.   10.0   12.5
> 75      /  6:    75.    62.    88.   12.5   12.5
> 100     /  7:   100.    88.   125.   12.5   25.0
> 150     /  8:   150.   125.   175.   25.0   25.0
> 200     /  9:   200.   175.   250.   25.0   50.0
> 300     / 10:   300.   250.   350.   50.0   50.0
> 400     / 11:   400.   350.   500.   50.0  100.0
> 600     / 12:   600.   500.   700.  100.0  100.0
> 800     / 13:   800.   700.   900.  100.0  100.0
> 1000    / 14:  1000.   900.  1100.  100.0  100.0
> 1200    / 15:  1200.  1100.  1350.  100.0  150.0
> 1500    / 16:  1500.  1350.  1750.  150.0  250.0
> 2000    / 17:  2000.  1750.  2500.  250.0  500.0
> 3000    / 18:  3000.  2500.  3500.  500.0  500.0
> 4000    / 19:  4000.  3500.  4500.  500.0  500.0
> 5000    / 20:  5000.  4500.  5000.  500.0    0.0