data transformation questions

[Stuart Maclean]

Hi Don, thanks for the prompt reply.

I did try the geosubsetting in idv 1.3b2, but it didn't quite do what I 
needed.  My subgrid is actually defined by grid points, or equivalently, 
kilometers, rather than lat lon as catered for by IDV.  My grid has a 
lambert conformal projection from x,y to lat,lon.  So I completed a nice 
netcdf filter app which takes index ranges for coordinate variables and 
uses Array.section to dice up the data.

Also, in trying to display my data (wind speed) in IDV as knots rather 
than ms-1, I don't see a 'Change Display Unit' in the Edit menu of the 
display control  (I tried all three Plan Views with same result).  The 
User's Guide mentions that 'Some displays allow you to change the unit 
that is used in the display' but doesn't state exactly which ones ?

Thanks again.

BTW if anyone is interested in my netcdf filter app, i can post it.

Stuart Maclean



Don Murray wrote:
> Hi Stuart-
> 
> Stuart Maclean wrote:
> 
>> I have a netcdf file of an mm5 model output. One variable is max wind 
>> speed, defined over a 2d grid, with values every 3 hours. The nc file 
>> has CF conventions in place so IDV can display it.
>>
>> I would like to perform two transformations on the data in order to 
>> display it in idv:
>>
>> 1 create a smaller area.  the orig grid is say 100x100 and I want to 
>> view just say an inner box of 20x20.  I know I can zoom in on the area 
>> but the mere presence of the full grid has influence on the 
>> contouring/display so I would prefer to clip the data first
> 
> 
> With the 1.3B2 release, if you double click on the data source
> in the Field Selector, it will bring up the dialog for setting
> the properties on that file (or right click and select
> Properties).  Under the Geo-Subsetting tab in the dialog, you
> can subset by stride (every Nth point) and/or by geographic
> location.  This will apply to any displays you create with
> that grid.   In the next release, you will be able to do
> this at the dataset or at the parameter level (like with
> Times).  This will clip the data and just read out what
> you have defined.
> 
>> 2 the units from the model are ms-1.  i would like to display (and 
>> contour) in knots.
> 
> 
> Once you have your display loaded, you can use the Display Control's
> Edit->Change Display Unit.. menu to set the unit to knots.  If
> you want this to be the default, then use the Parameter Defaults
> Editor (Edit->Resources->Parameter Defaults menu) to set the
> default unit for your variable.
> 
>> I suspect that the first task cannot be done in IDV.  I had hoped that 
>> NcML would provide some filtering leverage like this, but I haven't 
>> found it.
> 
> 
> Try the Geo-subsetting.
> 
>> The unit conversion can be done in IDV ??
> 
> 
> Yes.
> 
>> Any help gratefully appreciated
> 
> 
> If this doesn't work, let us know.
> 
> Don
> *************************************************************
> Don Murray                               UCAR Unidata Program
> dmurray at unidata.ucar.edu                        P.O. Box 3000
> (303) 497-8628                              Boulder, CO 80307
> http://www.unidata.ucar.edu/staff/donm
> *************************************************************
> 

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