On 4/9/07, Roger Bivand <[EMAIL PROTECTED]> wrote: > On Mon, 9 Apr 2007 [EMAIL PROTECTED] wrote: > > > For preview graphics and for large areas such as continents, large > > countries, hemispheres, or the whole earth, spherical projections are > > often adequate. I can provide some of the ones I have used. For > > detailed work at sites and small areas, ellipsoidal projections such as > > UTM are usually used, and then the coding gets more complicated with > > choices of datums and so forth. > > > > The attached script shows how to do the interrupted sinusoidal projection > using spTransform in rgdal, for the whemi.lin data posted with the > free-standing functions by Denis White a couple of days ago. Once the > lines are converted into SpatialLines objects, the rest is robust and > simple, as is the use of gridlines() in sp. The one catch is calculating > the offset, here in an x_0= offset along the Equator in metres between the > two central longitude values. The output is attached as a PNG image. The > point about the sp objects is that they contain enough metadata (here a > PROJ.4 projection description) to let them be moved to other R packages or > external software. > > The half-dozen basic projections are easy to specify in PROJ.4, for > example from the geotiff list: > > http://www.remotesensing.org/geotiff/proj_list/ > > which is what I used here. The other projections mentioned are: > > Lambert Cylindrical Equal Area "+proj=cea +lon_0=-80" > > Lambert Azimuthal Equal Area "+proj=laea +lat_0=0 +lon_0=-80" > > while the Northern hemisphere sinusoidal is: > > Sinusoidal "+proj=sinu +lon_0=-100" > > So I'd argue that PROJ.4 projection descriptions are not difficult to use, > and with sp objects, do stay stuck to the data (has anyone else ever > forgotten what projection was used when revisiting data, not just me?).
Yes, that's brilliant (keeping the proj4string). My point was not that proj is hard to use -- its simple -- rather that depending on proj means more build time dependencies. On the other hand, if its not broke.... THK -- Timothy H. Keitt, University of Texas at Austin Contact info and schedule at http://www.keittlab.org/tkeitt/ Reprints at http://www.keittlab.org/tkeitt/papers/ ODF attachment? See http://www.openoffice.org/ _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo