Re: [ferret_users] masking area

[DELCLAUX Francois <francois.delclaux@xxxxxxxxxxxxxxxxxxx>]

Hi Jaison and Ansley,
The problem is solved : my mask bv has a time axis indeed, and when
replacing bv[d=1] by bv[l=1, d=2] in the operation, I only get the 
warning message:
*** NOTE: Ambiguous coordinates on X axis: BV[D=1, L=1] * RAIN[D=2]
Thanks for your full explanation.

François Delclaux



> Hi Ansley,
>             In general, if the mask file doesnot have a time axis, there
> should not be any problem while applying the mask/making the plot after 
> that. Since Francois faced some error messgae, i assumed that there is 
> a time axis for the mask file (at least with one time point). That is why
> i explained about the messages in my earlier mail.
>
>  The other possibility for an error in masking is the incosistency of 
> X-Y grid as you mentioned earlier.
>
> Thanks & Regards,
>
> Jaison
>
> On Tue, 22 Aug 2006, Ansley Manke wrote:
>
>   
> > 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.
> > > >