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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
Hi John, you can find an example file under: http://pastebin.met.no/pastebin/cgi-bin/file?id=ccf557eaebc7d8757244577e9df70188914d3057/ice_conc_nh_200911291200_CF.nc The file contains sea-ice concentrations at the north-pole including a land mask. In the attached IDV-figure with McIdas borders, you can see that the islands between North-America and Asia have a offset of approx. 20km (2cells) to where they should be. I'm not 100% sure that the land-mask is correct. Usually I test those against IDV, but this test failed now. Best regards, Heiko 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 <Heiko.Klein@xxxxxx> >>> Sent: 09 March 2010 08:54 >>> To: Jonathan Blower <j.d.blower@xxxxxxxxxxxxx> >>> 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 >>> >> >> _______________________________________________ >> netcdf-java mailing list >> netcdf-java@xxxxxxxxxxxxxxxx >> For list information or to unsubscribe, visit: >> http://www.unidata.ucar.edu/mailing_lists/ > -- Dr. Heiko Klein Tel. + 47 22 96 30 00 Development Section / IT Department Fax. + 47 22 69 63 55 Norwegian Meteorological Institute http://www.met.no P.O. Box 43 Blindern 0313 Oslo NORWAY
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