Sorry, that was stupid, This: xyinv <- project(xysin, "+proj=longlat", inv=TRUE)
had to be: xyinv <- project(xysin, "+proj=sinu", inv=TRUE) problem solved.... Robert On Tue, May 19, 2009 at 10:29 AM, Robert Hijmans <r.hijm...@gmail.com> wrote: > I am confused about this behavior of rgdal > >> require(rgdal) >> # make a matrix of coordinates >> xygeo <- rbind(c(-180, 0), c(180,0), c(0,0), c(0,20), c(0,90)) >> # project to sinusoidial >> xysin <- project(xygeo, "+proj=sinu", inv=FALSE) >> # project back to longlat >> xyinv <- project(xysin, "+proj=longlat", inv=TRUE) >> xygeo > [,1] [,2] > [1,] -180 0 > [2,] 180 0 > [3,] 0 0 > [4,] 0 20 > [5,] 0 90 >> xyinv > [,1] [,2] > [1,] 180 0 > [2,] -180 0 > [3,] 0 0 > [4,] 0 126759249 > [5,] 0 573070423 >> > > Why are rows 4 and 5 different? > > > An illustration of the same problem, using 'raster' > >> library(raster) >> r <- raster(nrow=36, ncol=18, projs= "+proj=longlat") >> xy <- xyFromCell(r,1:ncell(r)) >> par(mfrow=c(1, 3)) >> plot(xy) # ok >> xysin <- project(xy, "+proj=sinu", inv=FALSE) >> plot(xysin) # nice >> xyinv <- project(xysin, "+proj=longlat", inv=TRUE) >> plot(xyinv) # ??? > > > Robert > >> sessionInfo() > R version 2.9.0 (2009-04-17) > i386-pc-mingw32 > > locale: > LC_COLLATE=English_United States.1252;LC_CTYPE=English_United > States.1252;LC_MONETARY=English_United > States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252 > > attached base packages: > [1] stats graphics grDevices utils datasets methods base > > other attached packages: > [1] rgdal_0.6-8 sp_0.9-34 > > loaded via a namespace (and not attached): > [1] grid_2.9.0 lattice_0.17-22 >> > _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
