National Oceanic and
Atmospheric Administration
United States Department of Commerce

Reversed Coordinates

Reversed Coordinates

Question:

Are there any disadvantages to using reversed coordinates?


Example:

> 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.

Explanation:

The ferret manual says the following about reversed-coordinate axes:

NetCDF axes may contain monotonically decreasing axis coordinatesinstead of monotonically increasing coordinates. Ferret will hide thisaspect of the file data ordering.

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

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


Last modified: Jul 17, 1997