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[Support #JXE-761208]: IDV with NetCDF including land (and IDV 2.7beta2)



Hi Liang-

> Hi,DonI uploaded two files,one is NYHOPS_noland.cdf, the other is NYHOPSFrom
> Table.cdf. With IDV 2.7,both can't be read in. But with IDV 2.6, the volume
> rendering is working perfect for the first cdf file,that's the file with no
> land  included. The second cdf file can't do the volume rendering work with
> IDV 2.6, in which land is included.
> 
> For IDV2.7,the error information is: couldn't get data 2 for the first cdf
> file.
> The error information is:Couldn't get data
> Gridded3DSet: samples values may not be missing. For the second cdf file.

There was a bug in the netCDF-Java stack that caused the problems with these
files for 2.7.  We actually came across that yesterday with another file and
the fix was checked into svn yesterday.  I'm not sure when that will
make it into our nightly build.

The 3D rendering with the missing lat/lons is tricky.  The netCDF library
replaces the xpos,ypos with the lat/lon values at each point.  For us
to handle the sigma coordinates, we make a mapping from lat,lon,sigma <-> 
lat,lon,altitude.  We do this so people can slice on sigma levels.
However, we can't do this when the lat/lons are missing because the 
transform is not invertible.   I'm still unclear why you have missing
lat/lons at any x,y if the grid can be mapped onto the earth. 

I don't really have a solution to that at this point, but will keep
pondering it.

Don

Don Murray
> address@hidden> wrote:
> 
> > Liang,
> > Please answer Don's questions below for me, with some detail, and upload on
> > his site:
> > 1) an example that does not work with 2.7 but works with 2.6, and
> > 2) the original (table.txt) version of the grid that does not render due to
> > land.
> > Please CC me in the response.
> > -Nickitas
> >
> > -----Original Message-----
> > From: Unidata IDV Support [mailto:address@hidden
> > Sent: Tuesday, June 02, 2009 4:57 PM
> > To: address@hidden
> > Cc: address@hidden
> > Subject: [Support #JXE-761208]: IDV with NetCDF including land (and IDV
> > 2.7beta2)
> >
> >
> > Hi Nickitas-
> >
> > > We took efforts to make our NetCDF output for our NY/NJ Harbor ocean
> > model
> > > CF-compliant, and now IDV renders it in 3D very nicely. We've seen
> > probes,
> > > transects, volume rendering. Very cool!
> >
> > Great!
> >
> > > BUT,
> > >
> > >
> > >
> > > Only if we create sub-arrays that do not include land (NaN lat-lon and
> > out
> > > of range packed values). This is a coastal ocean model, and as such, land
> > is
> > > part of the full output array. Because the grid is not a nice rectangle
> > but
> > > quite distorted in the X-Y, lat-long coordinate values on land would be
> > > nonsensical. But if we try to load the full output NetCDF CF-compliant
> > file
> > > with the native land/ocean array, IDV does not render in 3D.
> >
> > Is there a particular error that is generated?
> >
> > My guess is
> > > that IDV is trying to render the land parts of the array that are NaN and
> > > fails,  because it does not know how to distinguish between contiguous
> > areas
> > > of NaNs (such as land) versus internal NaN such as bad data, and does not
> > > know what to do with data gaps in general.
> > >
> > >
> > >
> > > Any clues? Have you come up with any smart ways of dealing with this
> > > problem? By the way, IDV 2.7 beta 2 does not work at all for us, only
> > 2.6,
> > > which is interesting in its own.
> >
> > We definitely want to fix what's broke in 2.7b2, so could you point
> > me to a sample data file or upload one to:
> >
> > http://motherlode.ucar.edu/repository/alias/idvupload
> >
> > Once we get that fixed, I can look further into the other issue.  Having
> > NaN's for lat/lon is tricky because the netCDF layer translates that into
> > a lat/lon projection.  If there is a dimensionless vertical coordinate,
> > that complicates it further since we have to have a transformation between
> > lat,lon,sigma <-> lat,lon,alt for the 3D displays.
> >
> > Don Murray
> >
> > Ticket Details
> > ===================
> > Ticket ID: JXE-761208
> > Department: Support IDV
> > Priority: Normal
> > Status: Open
> >
> >
> >
> 
> 


Ticket Details
===================
Ticket ID: JXE-761208
Department: Support IDV
Priority: Normal
Status: Open


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