Hi Rick,

Map projections can be done with the package proj4R developed by Roger

Bivand (

http://spatial.nhh.no/R/Devel/). Roger send me a development

version to use with R2.0.1.

This is the code I use to project to Albers equal area and UTM in South

Africa (the projection settings listed in the comments come from GRASS):

## Project data with proj4R

datSable.XY <- cbind(datSable$Longitude, datSable$Latitude)

## Albers Equal Area projection for SA

## elipse or datum WGS84

## false eastings 0

## false northing 0

## central meridian 24

## stand parr_1 -18

## stand parr_2 -32

## lat of origin 0

## output of project is a matrix!

datSable.XYaea <- project(datSable.XY, "+proj=aea +ellps=WGS84

+lon_0=24 +lat_0=0 +lat_1=18s +lat_2=32s +x_0=0 +y_0=0 ")

nrow(datSable.XYaea)

tmp <- data.frame(datSable.XYaea)

datSable <- data.frame(datSable, Xaea=tmp$X1, Yaea=tmp$X2)

# name: UTM

# datum: WGS84

# towgs84: 0.000,0.000,0.000

# proj: utm

# ellps: wgs84

# a: 6378137.0000000000

# es: 0.0066943800

# f: 298.2572235630

# zone: 36

# south: defined

datSable.XYutm <- project(datSable.XY, "+proj=utm +ellps=WGS84

+zone=36S +south +units=m ")

This should work on polygon coordinates to!

The packages maps and maptools might provide a solution to the area of

the polygons.

Let me know what you manage to do. I am trying similar things: see

earlier posts on the r-geo list.

Cheers,

Sander.

Rick Reeves wrote:

>

> Hello:

>

> I've searched the literature, havent found an answer, so here goes?

>

> We have a set of polygon features defined as a series of unprojected

> vertices represented by lat/long pairs, in an ASCII-format file.

>

> We need to display (on a map-like plot) and then calculate the areas

> of the polygons, and would like to do this entirely within R if

> possible.

> Is there a map projection package for R? Or, has anyone solved this

> or a related problem using R? I could do this with the MATLAB mapping

> toolbox, but prefer to use R if possible....

>

>

> Thanks,

>

> Rick Reeves

>

> Scientific Programmer / Quantitative Analyst

> National Center for Ecological Analysis and Synthesis

> University of California, Santa Barbara

> 805 892 2534

> reeves at nceas.ucsb.edu

>

> _______________________________________________

> R-sig-Geo mailing list

> R-sig-Geo at stat.math.ethz.ch

>

https://stat.ethz.ch/mailman/listinfo/r-sig-geo>

--

--------------------------------------------

Dr. Sander P. Oom

Animal, Plant and Environmental Sciences,

University of the Witwatersrand

Private Bag 3, Wits 2050, South Africa

Tel (work) +27 (0)11 717 64 04

Tel (home) +27 (0)18 297 44 51

Fax +27 (0)18 299 24 64

Email sander at oomvanlieshout.net

Web www.oomvanlieshout.net/sander