Re: reversed-coordinate axes

[hankin@xxxxxxxxxxxxxxxxxxx (Steve Hankin)]

Hi Emilio,

There are only very minor performance issues from using a reverse-ordered axis
in Ferret. When reading a large chunk of data, the amount of memory used will
be momentarily doubled -- an issue in a few cases.

Ferret will hide the reversal of the axis in almost every way. The SHOW GRID
command, for example, will show the coordinates in **increasing** order. When
you write out a NetCDF file using Ferret (using the SAVE command) you will find
that Ferret has reordered the data and coordinates in the file to increasing
order.

	- steve

=========================================================================

On May 30, 10:36am, Emilio Mayorga wrote:
> Subject: reversed-coordinate axes
> The ferret manual says the following about reversed-coordinate axes:
>
> 3.5.6 Reversed-coordinate axes
>
> NetCDF axes may contain monotonically decreasing axis coordinates
> instead of monotonically increasing coordinates. Ferret will hide this
> aspect of the file data ordering.
>
>
> My question is: are there *any* limitations or disadavantages to using
> reversed-coordinates? Are computations less efficient? I want to write
> my netcdf files using monotonically *decreasing* latitude coordinates,
> to make the file more directly compatible with the preferences of other
> software; for instance, right now if I use something like
> SET REGION/ *an XY region at one time step*
> LIST/FORMAT="STREAM"/FILE="uff.bil" uffvariable
> the raw binary image will come out "upside down", because that's how the
> data is written in the netcdf file.
>
> Thanks.
>
> Emilio Mayorga
> ________________________________________________________________
> University of Washington
> School of Oceanography			emiliom@u.washington.edu
> Box 357940				ph. (206) 543-5334
> Seattle, WA  98195-7940	  USA		FAX (206) 685-3351
> http://boto.ocean.washington.edu/staff_pages/emilio
>-- End of excerpt from Emilio Mayorga




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