Re: [netcdf-java] ncWMS and ellipsoid-support in CF-1.2

On 6/9/2010 7:08 AM, Heiko Klein wrote:
> Hi John,
>
> when we discussed the issue of ellipsoid-support in netcdf-java back in
> March in the mailing-list it went very fast to: use one or another GeoAPI.
>
> This sounded to me like a lot of work for you. If you don't plan to do
> this work in the near future (i.e. 2010), could you please send me the
> proj4j source. Maybe I can try then to add ellipsoid support of
> Stereographic and Transverse Mercator to netcdf-java (4.2) during summer.
>
> Best regards,
>
> Heiko
>    

Hi Heiko:

Im not sure how fast i can get to that. Do you have real datasets with 
those projections?

The proj4 code is from the jhlabs partial port at

http://www.jhlabs.com/java/maps/proj/index.html

The ones that ive already done are at

http://svn.unidata.ucar.edu/repos/common/java/trunk/src/main/java/ucar/unidata/geoloc/projection/proj4/

I should warn you that I have seen bugs in the Java, which i think is 
some automatic C/Java translater. I have been checking against the 
original C code. Also, theres a lot of modifications to be made to make 
it compatible with our Projection class. Thats why the Geotools API may 
be a better idea.

BTW, Transverse Mercator on the ellipsoid i think is UTM, which we have. 
So perhaps you only need Stereographic ?

John


> On 2010-03-24 17:46, John Caron wrote:
>    
> > Heiko Klein wrote:
> >      
> > > Hi Jon,
> > >
> > > I just found some time to look at the source of netcdf-java 4.1. As far
> > > as I can see, only some projections (LambertConformalConicEllipse,
> > > AlbersEqualAreaEllipse, UTM) support ellipsoids, while the others use a
> > > constant spherical earth with EARTH_RADIUS = 6371.229km
> > >
> > > In particular, Stereographic projection doesn't support ellipsoids, so
> > > this explains the offset in my maps.
> > >
> > > Would be nice to have this assured by one of the unidata-developpers. I
> > > mainly checked the ucar/unidata/geoloc/projection sources.
> > >
> > > Best regards,
> > >
> > > Heiko
> > >        
> > Yes, correct. We are slowly adding ellipsoid support, but only after we
> > have a sample dataset that uses them. We are porting code from proj4,
> > its rather time-consuming to get it right.
> > if you have sample data where the ellipsoidal earth matters, send it
> > along, we'll get to it when we can. or, if you have resources and
> > expertise to port the proj4j code, i could send that to you and get you
> > started.
> >
> > John
> >
> >      
> > > On 2010-03-10 14:38, Jonathan Blower wrote:
> > >        
> > > > Hi Heiko,
> > > >
> > > > This is a good question.  ncWMS relies on netcdf-java for converting
> > > > coords to wgs84 lat lon, so I'm copying this to the mailing list in
> > > > the hope that someone can enlighten me about ellipsoid support in the
> > > > library.
> > > >
> > > > Cheers, Jon
> > > >
> > > > -----Original Message-----
> > > > From: Heiko Klein<address@hidden>
> > > > Sent: 09 March 2010 08:54
> > > > To: Jonathan Blower<address@hidden>
> > > > Subject: ncWMS and ellipsoid-support in CF-1.2
> > > >
> > > > Hi Jon,
> > > >
> > > > I currently try to visualize some satellite ice-maps over the north-pole
> > > > with ncWMS, but the data seems to be displaced by some 10-30km compared
> > > > with the land-maps (generated by mapserver).
> > > >
> > > > While geo-tools and therefore ncWMS support lots of coordinate reference
> > > > systems for the presented maps, the support for ellipsoids was only
> > > > added to CF-1.2. Do you know if ncWMS already supports the CF-1.2
> > > > features like semi_major_axis/semi_minor_axis for input-files, or does
> > > > it assume the CF-1.0 spherical earth with 6371km radius?
> > > >
> > > > Best regards,
> > > >
> > > > Heiko
> > > >
> > > >          
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> >