[R-sig-Geo] Good projection for N/S America?
Roger Bivand
Roger.Bivand at nhh.no
Mon Apr 9 22:52:45 CEST 2007
On Mon, 9 Apr 2007 White.Denis at epamail.epa.gov 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.
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 <tkeitt at gmail.com> 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 <Roger.Bivand at nhh.no> wrote:
> > > On Mon, 9 Apr 2007 White.Denis at epamail.epa.gov 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
> > >
> > > > r-sig-geo-bounces at stat.math.ethz.ch 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, White.Denis at epamail.epa.gov
> <White.Denis at epamail.epa.gov>
> > > > 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)
> > > > > >
> > > > > > r-sig-geo-bounces at stat.math.ethz.ch 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 White.Denis at epamail.epa.gov 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 <tkeitt at gmail.com> 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, White.Denis at epamail.epa.gov
> > > > > > <White.Denis at epamail.epa.gov>
> > > > > > > > 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)
> > > > > > > > > >
> > > > > > > > > > r-sig-geo-bounces at stat.math.ethz.ch 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 at 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: Roger.Bivand at nhh.no
> > > > > > >
> > > > > > > _______________________________________________
> > > > > > > R-sig-Geo mailing list
> > > > > > > R-sig-Geo at 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 at stat.math.ethz.ch
> > > > > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> > > >
> > > > _______________________________________________
> > > > R-sig-Geo mailing list
> > > > R-sig-Geo at 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: Roger.Bivand at nhh.no
> > >
> > >
> > >
> >
> >
> > --
> > 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: Roger.Bivand at nhh.no
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