Re: [ferret_users] masking area

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

Hi Jaison and Francois,
I don't think there need be any messages about Ambiguous coordinates on 
the T axis. Here is an example, creating a MASK variable from one of the 
ETOPO datasets making sure it's on the same grid as the data variable, 
which is just a data set having a time axis accessed by an OPeNDAP 
address.  The first part of this is just creating an example mask.

! Look at the data variable and grid

yes? USE 
"http://ferret.pmel.noaa.gov/NVODS-FDS/LAS/COADS_2-degree_Standard/air1672";
yes? SHOW DATA
    currently SET data sets:
   1> 
http://ferret.pmel.noaa.gov/NVODS-FDS/LAS/COADS_2-degree_Standard/air1672  
(default)
name     title                             I         J         K         L
AIR      Air Temperature Monthly 1st Sext 1:180     1:90      ...       
1:2472

! Create a mask on the same XY grid

yes? USE etopo60
yes? LET mask = IF  rose[GXY=air[d=1]] GT (-3000) THEN 1
yes? SAVE/CLOBBER/FILE=mask.nc mask
LISTing to file mask.nc

yes? CANCEL DATA/ALL
yes? CANCEL VAR/ALL

! Now use the same data and the mask we just made

yes? USE 
"http://ferret.pmel.noaa.gov/NVODS-FDS/LAS/COADS_2-degree_Standard/air1672";
yes? USE mask.nc

yes? LET masked_air = mask[D=2] * air[D=1]
yes? SET VIEW ul

yes? SHADE/T=1-jan-1990 masked_air; GO land


! show the original data and the mask...

yes? SET VIEW ll
yes? SHADE/T=1-jan-1990 air[D=1]; GO land
yes? SET VIEW lr
yes? SHADE mask[D=2]; GO land



Jaison Kurian wrote:
> Hi,
>     If the mask variable "bv" is not having "any" time points, there
> should not be any problem while multiplying "bv" with "rain". In this
> case the show data command for "bv" should show empty Z and T axes as
> follows:
>
>  name   title                     I         J     K       L
>  BV     Basin Mask              1:180     1:90   ...     ...
>
> Suppose you have one time point for the variable bv, for L=1, there
> will be a warning message as follows :
>
>   "*** NOTE: Ambiguous coordinates on T axis: RAIN[D=1]*BV[D=2]"
>
> This can be ignored. But from the second time point onwards the 
> "rain*bw" will start complining as :
>
>  **ERROR: illegal limits: BV is not in the range L=2
>           Axis extremes are L=1
>
> In this case you have to specify L=1 while multipling with rain
> ..like
>
>    let rain_basin = rain[d=1] * bv[d=2,l=1]
>   
> This will fix the problem.
>
> If these tips doesnot help you, please send me the output of 
> "show data" command for those two datasets along with the error
> messages (& multiplication line from the Ferret script).
>
> Regards,
>
> Jaison 
>
> On Tue, 22 Aug 2006, DELCLAUX Francois wrote:
>
>   
> > Hi Ferret users,
> > I would like to compute  spatial and temporal average rainfall on a 
> > watershed.
> > The watershed is  a  (x,y) netcdf file (variable bv) (0 outside the 
> > basin, 1 inside the basin)
> > Rainfall field is a (x,y,t) netcdf file, (variable rain) with same 
> > spatial resolution as watershed.
> > So I have supposed that mutiplying rain by bv, I would get a rainfall 
> > field inside the wathershed.
> > But Ferret does not accept to multiply a (x,y) variable by a (x,y,t) 
> > variable.
> >
> > In ferret documentation, masking  areas are defined from 3d fields, so 
> > multiplication
> > are possible. But not in my case.
> >
> > How can I do this quite simple operation ?
> >
> > Thanks in advance.
> >
> >