[R-sig-Geo] projecting Lat and Long to 2D

Agustin Lobo aloboaleu at gmail.com
Wed May 14 09:02:34 CEST 2008

If your sites are more or less all over the world,
why do you want to project? The Earth is not flat.
If this is just for cartographic display,
you can use goode homolosine for example
(http://en.wikipedia.org/wiki/Goode_homolosine_projection). But for
calculating distances, the most reasonable is
using geodesic distance.


Harry Kim wrote:
> Dear R-sig-Geo listers,
>      These are very newbie like questions but if i could get any kind of
> help, i would very much appreciate it.
>      I am trying to project points encoded in latitude and longitude to
> hopefully Cartesian coordinates with a reasonable unit of distance
> (meters or kilometers.) When i encountered this problem previously,
> i've used PBSmapping package and convUL() to convert the points to
> UTM coordinates.
>      However, the points that i wish to project now are all over eurasia
> and Africa. I feel that if i just naively convert all the points to
> UTM, then i will run into a trouble as the points have different UTM
> zones. Is this correct? If i have some points in zone 10 and zone 14,
> and wish to find the distance between them using UTM coordiates and
> euclidean norm, would it provide a reasonable approximation of their
> distance? If not, is there a projection you would recommend that will
> give me a reasonable results?
>      I would also like to overlay the points with a world map excluding
> America and Antartica. I know that i can plot the map of the world
> using maps package and map("world",regions="") but i don't know how i
> would exclude the two continents.
>      I tried to export the world map into a shapefile then read it in to R
> using readShapPoly() in maptools package, then change the coordinate
> system into UTM using spTransform, but this ended up giving me a very
> weird looking figure.
>      In sum, i would like to know if there is a good way to project these
> points and overlay a map such that i can use euclidean norm to find
> the distance, and the map won't look completely bizzare. Also i would
> like to know if i could exclude the two continents mentioned: the
> America and the Antarctica.
> I thank you very much in advance and i hope you are having a pleasant day.
> Harry
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Dr. Agustin Lobo
Institut de Ciencies de la Terra "Jaume Almera" (CSIC)
LLuis Sole Sabaris s/n
08028 Barcelona
Tel. 34 934095410
Fax. 34 934110012
email: Agustin.Lobo at ija.csic.es

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