[R-sig-Geo] Good projection for N/S America?

Mon Apr 9 18:00:35 CEST 2007

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.

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
> > >
> > > _______________________________________________
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> > > 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/
>
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