Roger Bivand <[EMAIL PROTECTED]> wrote on 2007-04-09 13:52:45: > On Mon, 9 Apr 2007 [EMAIL PROTECTED] wrote: > > > Roger's solution makes sense to me. > > > > The sinusoidal does have the appearance of pinching poleward, a > > consequence of allocating equal area by spacing equally in both x and y. > > Both Canada and Norway - especially including Spitzbergen - suffer from > this, but good compromises are hard to find if one needs Patagonia too.
Goode's Homolosine is one. USGS distributes (or did) some of their global land cover data in that projection, see http://landcover.usgs.gov/globallandcover.php. Not only is it interrupted, but it combines the sinusoidal from -40 to +40 and the Mollweide poleward of +/- 40. (I don't see it on the geotiff list.) > I can see that getting rgdal binaries for popular platforms is a real > issue, any suggestions? > > Roger > > > Also the Lambert cylindrical sent in before should have had standard > > parallels set to +/- 30, i.e., > > > > (See attached file: whemi.projs.png) > > > > Tim Keitt <[EMAIL PROTECTED]> wrote on 2007-04-09 13:38:33: > > > > > Canada looks pinched in this projection. S. Am is perfect. > > > > > > THK > > > > > > 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?). > > > > > > > > Using the maptools map2SpatialLines() interface function, or the > > Rgshhs() > > > > interface to GSHHS shorelines, even getting the lines is quite easy, > > > > qualified by clipping and bounding box issues in extremities for > > > > projection from geographical coordinates. > > > > > > > > Of course, it would help to have MacOS X and selected Linux binaries > > of > > > > rgdal, we're very lucky that Uwe Ligges is so helpful with the > > Windows > > > > binaries. > > > > > > > > Roger > > > > > > > > > [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 > > > > > > > > > > > > > -- > > > > 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] > > > > > > > > > > > > > > > > > > > > > -- > > > 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
