Hello, I am trying to use sea ice concentrations data (spatial resolution=25 km) from the NSIDC database: http://nsidc.org/data/docs/daac/nsidc0051_gsfc_seaice.gd.html#spatialcover but data are projected in a modified version of the "polar stereographic projection" (projection plane or grid tangent to the Earth's surface at 70 degrees + Hughes ellipsoid). The parameters of this projection are available in their website and I found an epsg code on "spatial reference" website _http://spatialreference.org/ref/epsg/3412/_ ("epsg=3412), however I could not figure out how to project these data in WGS84.
The data are in binary format :download : _ftp://sidads.colorado.edu/pub/DATASETS/seaice/polar-stereo/nasateam/final-gsfc/south/monthly/_ sic.data <- matrix(data=readBin("C:\\nt_200712_f13_v01_s.bin", "integer", n=316*332, size=1, signed=FALSE), ncol=316, byrow=TRUE) The sea ice data are projected in the particular version of the "polar stereographic projection" image(sic.data) but I'm not sure whether this image is "correctly " projected or need to be modified with the provided lats and longs files : _ftp://sidads.colorado.edu/pub/DATASETS/seaice/polar-stereo/tools/_ sic.lat <- matrix(data=readBin("C:\\Sea Ice NSIDC reso_25km\\polar-stereo\\nasateam\\pss25lats_v2.dat", "integer", n=316*332, size=4, signed=FALSE, endian="little"), ncol=316, byrow=TRUE) sic.lon <- matrix(data=readBin("C:\\Sea Ice NSIDC reso_25km\\polar-stereo\\nasateam\\pss25lons_v2.dat", "integer", n=316*332, size=4, signed=FALSE, endian="little"), ncol=316, byrow=TRUE) that we need to divide by 100000 : sic.lat <- sic.lat/100000 sic.lon <- sic.lon/100000 But these coordinates are not those of the special version of the "polar stereographic projection" but look like WGS84 coordinates... I am looking for a way to match these 3 matrix so that I can use the sea ice concentrations data with WGS84 coordinates... I tried : lon <- as.vector(sic.lon) lat <- as.vector(sic.lat) sic <- as.vector(sic.data) SIC <- SpatialPoints(data.frame(sic = sic.data*0.4, lon = sic.lon, lat = sic.lat), proj4string=CRS("+init=epsg:3412")) SIC2 <- spTransform(SIC, CRS=CRS("+proj=latlong +ellps=WGS84")) but it does look like it should... Has anybody already used these kind of data ? Many thanks for your reply Clara Péron ************************************************ Clara Péron PhD Student Spatial distribution of seabirds in the Indian Austral Ocean Centre d'Etudes Biologiques de Chizé - CNRS UPR1934 79360 Villiers-en-Bois, France http://www.cebc.cnrs.fr/Fidentite/peron/peron.htm ************************************************ __________ Information from ESET Mail Security, version of virus signature database 4503 (20091013) __________ The message was checked by ESET Mail Security. http://www.eset.com [[alternative HTML version deleted]]
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