Re: [ferret_users] Lat/long to openDAP indices conversion

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

Hi Tiho,
Ferret makes calls to the NetCDF library for all OPeNDAP I/O requests. 
Current versions of Ferret are linked with NetCDF v4.1.1.  When you open 
the dataset URL with a USE statement, Ferret reads and stores the 
dimension and coordinate information as well as the variable names and 
their attributes. When you request a subset, the conversion between 
coordinates and indices is done using the coordinate values (which are 
stored by Ferret as double precision values). Then when you read a 
subset of data, the appropriate call is made to the NetCDF library to 
actually read that subset of the data.

-Ansley

On 7/21/2010 9:19 PM, Tiho.Beretovac@xxxxxxxx wrote:
> Hi there,
>
> New to ferret, but have tried for a while and have been unable to find an answer to this question:
>
> How does ferret convert the lat long bounding box constraints it uses into indices of individual OpenDAP requests when it fetches the data from an OpenDAP source.
>
> For instance, if you point ferret to an OpenDAP source and ask for a FILL\x=130e:140e (ie. lat long based request), this is translated into an OpenDAP fetch with something like ?mydata[0][32:85][0:499] (ie. the indices that represent the data within the eastings and northings specified in the ferret request).
>
> Are the specifics of this conversion explained anywhere?
> Any insight appreciated.
>
> Cheers,
>
> Tiho
>
>