On Tue, 10 Apr 2007, Roger Bivand wrote: > On Mon, 9 Apr 2007 [EMAIL PROTECTED] wrote: > > > 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.) > > projInfo() in rgdal gives a list of supported projections, here: > > +proj=goode +lon_0=-80 > > and a PNG is attached. However, in rgdal on one platform I'm seeing an > EDOM (trig/math function out of domain) that I don't see running proj > through system(). The grid is OK, so there may be a weakness in the > project/transform interface in this case - I'm looking into it. Like the > PROJ.4 sinusoidal, it disregards the ellipsoid anyway, just spherical.
Following this problem up, I have improved error handling in project() and spTransform() in rgdal, but there is a problem with "+proj=goode" on some platforms (not the current Windows binary), which seems to get muddled when switching across +/- 40d44m (in proj source file pj_goode.c) or 40d44m12s (Snyder p. 249). Running "+proj=moll" or "+proj=sinu" on the same data is not a problem on the affected platform(s). My suspicions are that there are differences in compiler headers between the proj library and the rgdal/R binaries, which may be platform dependent - my affected platforms are RHEL 4. Roger > > I haven't checked whether the same offset approach can be used to split > the Northern and Southern hemispheres, but I don't see why not, given > that this is mostly sinusoidal. > > Roger > > > > > > 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] > > > > > > > -- 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