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.
[EMAIL PROTECTED] wrote on 2007-04-08 07:56:03: > Denis, > > That's really useful. It occurs to me that we only really need a > half-dozen basic projections to cover 90% of user cases. Perhaps these > could be incorporated into the 'sp' group somewhere and relieve the > dependence on proj4. (It could be packaged separately for R for the > other 10% of cases where its needed.) > > THK > > On 4/6/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: > > Thanks, Roger. There was a request to see the R code for these figures. > > Attached is the script for the second PDF file plus the input boundary > > file I used for the hemisphere. The three projection functions are for > > simple spherical, rather than ellipsoidal, models of the earth. The > > graticule generating function could be more elegant. I'm not yet up to > > speed with sp and the many new spatial capabilities in R so please > > excuse the old style "lines()" format encoding and graphics. > > > > Tim, I don't know whether proj4 could do the interrupted sinusoidal. > > > > (See attached file: whemi.projs.r)(See attached file: whemi.lin) > > > > [EMAIL PROTECTED] wrote on 2007-04-06 04:51:53: > > > > > Since this topic is of general interest, I've made an exception and > > > allowed (this once!) a posting of more than 200K. In general, if > > graphics > > > are big, please consider either an alternative device (png is often > > OK), > > > or posting just a URL to the real file. > > > > > > With apologies to list members on dial-up connections in the field, > > > > > > Roger > > > > > > > > > On Thu, 5 Apr 2007 [EMAIL PROTECTED] wrote: > > > > > > > Yes, for many uses that is my choice also. For the conterminous US > > for > > > > example, the Lambert azimuthal has lower mean distortion than the > > > > commonly used standard projection, the Albers conical equal area, > > > > although Albers was chosen by USGS as a standard because of lower > > > > extreme distortion than many other possible projections. > > > > > > > > For our hemispherical application, because we were gridding the > > data, we > > > > wanted parallels of latitude to be parallel in the projected > > coordinate > > > > space, which we wouldn't get with the Lambert azimuthal. > > > > > > > > (See attached file: whemi.projs.pdf) > > > > > > > > Tim Keitt <[EMAIL PROTECTED]> wrote on 2007-04-05 10:56:09: > > > > > > > > > Thanks. My application is not that demanding. Really, I just want > > it > > > > > to look reasonable. My plan is to lay out the postings in the > > > > > projected coordinates and then back transform into geographic > > > > > coordinates for analysis. I tried lots of projections and found > > > > > Lamberts Azimuthal Equal Area to be quite good. I like the look of > > the > > > > > Azimuthal Equidistant better, but figured equal area was a good > > > > > choice. > > > > > > > > > > THK > > > > > > > > > > On 4/4/07, [EMAIL PROTECTED] > > <[EMAIL PROTECTED]> > > > > wrote: > > > > > > Tim, > > > > > > > > > > > > It depends on which kind of distortion is of most concern. For > > many > > > > > > types of extensive data, especially counts, for example, the > > equal > > > > area > > > > > > property is desirable. We used the Lambert cylindrical equal > > area > > > > > > projection with standard parallels of +/- 30 degrees for some > > > > western > > > > > > hemispherical work, see reference below. (The center longitude > > > > could be > > > > > > -80 west, but that is less important than the choice of > > parallels.) > > > > > > > > > > > > Before falling back on the Lambert as an easy to use projection, > > I > > > > tried > > > > > > to get several ESRI products to implement an interrupted > > projection > > > > > > using the sinusoidal projection, in part for reasons given in > > the > > > > second > > > > > > reference. I used a separate center longitude for north and > > south > > > > of > > > > > > the equator and the appearance is certainly more satisfactory > > than > > > > the > > > > > > Lambert in my opinion. I'll attach a PDF of an illustration of > > this > > > > > > approach generated in R that I hope you will get but not the > > rest of > > > > the > > > > > > list unfortunately. I can send PDFs of the references also if > > > > needed. > > > > > > > > > > > > Denis > > > > > > > > > > > > Lawler JJ, White D, Neilson RP, Blaustein AR. 2006. Predicting > > > > > > climate-induced range shifts: model differences and model > > > > reliability. > > > > > > Global Change Biology 12:1568-1584. > > > > > > > > > > > > White D. 2006. Display of pixel loss and replication in > > > > reprojecting > > > > > > raster data from the sinusoidal projection. Geocarto > > International > > > > > > 21(2):19-22. > > > > > > > > > > > > (See attached file: whemi.sinus.pdf) > > > > > > > > > > > > [EMAIL PROTECTED] wrote on 2007-04-04 > > 12:17:39: > > > > > > > > > > > > > Anyone know of a particularly good map projection for showing > > all > > > > of > > > > > > > North and South America without too much distortion? > > > > > > > > > > > > > > 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 > > > > > > > > > > > > > > > > > > > > > -- > > > > > 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/ > > > > > > -- > > > Roger Bivand > > > Economic Geography Section, Department of Economics, Norwegian School > > of > > > Economics and Business Administration, Helleveien 30, N-5045 Bergen, > > > Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 > > > e-mail: [EMAIL PROTECTED] > > > > > > _______________________________________________ > > > R-sig-Geo mailing list > > > R-sig-Geo@stat.math.ethz.ch > > > https://stat.ethz.ch/mailman/listinfo/r-sig-geo > > > > > -- > 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 _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
