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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