Re: [ferret_users]

[Ryo Furue <furue@xxxxxxxxxx>]

Hi Lívia,

> Dear fellows, I'm trying to isolate the velocity field of a water
> parcel through a density interval.
[. . .]
> yes? fill uvel
> 
> **ERROR: command syntax: Unknown transformation:5500
>           Use SHOW TRANSFORMS for a list of legal transformations

This error seems to be from your "z=0:5500@int".  I don't think there
is a transformation "@INT".

I'm not quite sure what do you mean by "isolate the velocity field".
With this definition

> let water1 = if (sigma ge 1027.6 and sigma le 1027.8) then u[d=3]

your water1 is the same as u[d=3] only where 1027.6 < sigma <= 1027.8
and it's undefined elsewhere.

If you want to integrate the velocity field within this density class,
probably this is what you want:

  let uvel = water1[z=0:5500@din]

"@DIN" is a definite integral.  I'm not sure whether this method
has enough accuracy for your purpose; because in this calculation
there is no interpolation but the gridboxes with density values
outside the range are simply ignored in the integration.

Ryo