Re: [netcdf-java] GridCoordSys introduces rounding error when converting from km to m and integer axis-type

[John Caron <caron@xxxxxxxxxxxxxxxx>]

Heiko Klein wrote:
> Hi John,
>
> you can download a file from 
> http://pastebin.met.no/pastebin/cgi-bin/file?id=84f2552e57e811173f846941bfab295a733bb219/mipom_nordic4_inM_small4.nc 
>
>
> We've been using the file through thredds/WCS and it didn't give a 
> bounding-box in GetCapabilities. Changing the axes datatype to double 
> solved the problem.
>
> I guess, the problem lies in:
> private CoordinateAxis convertUnits(CoordinateAxis axis) {
>     ....
>     Array data;
>     try {
>       data = axis.read();
>     ....
>     IndexIterator ii = data.getIndexIterator();
>     while (ii.hasNext())
>       ii.setDoubleCurrent(factor * ii.getDoubleNext());
>     ....
> with data having the same datatype as axis.

yes, thats the problem, thanks for figuring it out. Ill have to figure out 
a workaround, i guess i should promote to double. it sounds like you have a fix 
for now?


> > > The class ucar.nc2.dt.grid.GridCoordSys converts internally all 
> > > projection-axes to km. But it seems like it does not convert the 
> > > datatype to a float or double datatype and introduces therefore large 
> > > rounding errors.
> > >
> > > I have given my axes as m (in integer):
> > > -3716017, -3712004, -3707991
> > >
> > > The isRegular function of Coordinate1D sees (with a debugger attched) 
> > > the values:
> > > -3716, -3712, -3707
> > > and as such fails with my approx. 4km grid-distance.
> > >
> > >
> > >
> > > Best regards,
> > >
> > > Heiko