[gdal-dev] geolocation info in netCDF: "northernmost_northing" etc. not universal

[Kyle Shannon]

I am also using the netCDF driver to read weather data from a thredds
server.  I am curious how the tag names for the metadata were defined in the
driver.  For example, the CF convention for the central meridian is
"longitude_of_central_meridian" and in the netCDF driver it is
"central_meridian".  This causes the true value to be skipped and set to a
default value of 0.0 in my case.

regards,

# ===================
Kyle Shannon
Physical Science Technician
RMRS Fire Sciences Lab
Fire, Fuels & Smoke - RWU 4405
5775 Highway 10 W.
Missoula, MT 59808
(406) 829-6954
kshannon at fs.fed.us
# ===================


On Thu, Jan 28, 2010 at 3:52 PM, Bruce Raup <bruceraup at gmail.com> wrote:

> Frank,
>
> Thanks for the reply.  I mistakenly said GeoRef when I meant to say
> GeoTransform.  Your description of what would happen if we make the
> change confirms what we thought.
>
> I think we will go ahead and make the change, and file a ticket.  Lots
> of data are in polar projections, and it seems like a small amount of
> work now could save a lot of confusion in the future.
>
> Best regards,
> Bruce
>
>
> On Wed, Jan 27, 2010 at 17:44, Frank Warmerdam <warmerdam at pobox.com>
> wrote:
> > On Wed, Jan 27, 2010 at 2:22 AM, Bruce Raup <bruceraup at gmail.com> wrote:
> >
> >> We propose using terms such as
> >>
> >> grid_top_boundary_projected_y
> >> grid_bottom_boundary_projected_y
> >> grid_left_boundary_projected_x
> >> grid_right_boundary_projected_x
> >>
> >> Alternatively, grid corner coordinates could be used.
> >>
> >> What would the impacts of such a change of names in our files be?  If
> >> the GeoRef field is also in the file, would it break existing software
> >> for being able to navigate (geolocate) the data?  And, would the
> >> community consider the adoption of more universal terms more generally
> >> (i.e. in GDAL itself)?
> >
> > Bruce,
> >
> > I am not really an expert on the GDAL netcdf driver, but
> > I will attempt to respond.
> >
> > First, I think it would be better to just document that the
> > existing tag names (eg. northernmost_northing) should
> > just be interpreted with the new definitions
> > (grid_top_boundary_projected_y) rather than trying
> > to change the actual tag names in order to gain some
> > possibly clarity in less common situations.
> >
> > I have reviewed the GDAL netcdf driver and it seems to
> > look for two things.  First a GeoTransform value (which I
> > think is only a GDAL convention).  If that is not found it
> > looks for northernmost_northing, etc.  I presume these are
> > part of the CF conventions, though I don't know for sure.
> >
> > I do no see any reference to a "GeoRef" tag.
> >
> > So if you make the planned change, and if you do not
> > also provide the GeoTransform then older versions of
> > GDAL would not be able to read the georeferencing of
> > the files.  I presume this might also be the case of
> > almost all other software, even if you did support
> > GeoTransform.
> >
> > However, if you do go ahead with this convention, then
> > please file  ticket with a small sample file so we can add
> > support for it.
> >
> > Best regards,
> > --
> >
> ---------------------------------------+--------------------------------------
> > I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> > light and sound - activate the windows | http://pobox.com/~warmerdam<http://pobox.com/%7Ewarmerdam>
> > and watch the world go round - Rush    | Geospatial Programmer for Rent
> > _______________________________________________
> > gdal-dev mailing list
> > gdal-dev at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/gdal-dev
> >
>
>
>
> --
> Bruce Raup
> http://cires.colorado.edu/~braup/ <http://cires.colorado.edu/%7Ebraup/>
> _______________________________________________
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>
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