[R-sig-Geo] azequidistant map projection

[Roger Bivand]

On Mon, 17 Dec 2007, Justin Parrella wrote:

> Hi,
> I'm using the map projection azequidistant(), but can't find
> documentation on what units the output is given in. Does anyone know?

It is not documented on the mapproject() help page, and it would be most 
helpful if it was (CC to maintainer). From experience, the output 
coordinates from mapproject() seem to be in some kind of screen graphics 
coordinates, not related in any direct way to units on the ground:

library(mapproj)
dta <- map("world", xlim=c(-120, -60), ylim=c(0,90), plot=FALSE)
plot(dta, type="l")
plot(mapproject(dta, projection="azequidistant"), type="l")
library(maptools)
dta1 <- map2SpatialLines(dta)
summary(dta1)
proj4string(dta1) <- CRS("+proj=longlat")
summary(dta1)
plot(dta1, axes=TRUE)
library(rgdal)
dta2 <- spTransform(dta1, CRS("+proj=aeqd +lat_0=45 +lon_0=-90"))
summary(dta2)
plot(dta2, axes=TRUE)

uses PROJ.4:

http://www.remotesensing.org/geotiff/proj_list/azimuthal_equidistant.html

which also allows you to set parameters. The units are in meters.

Hope this helps,

Roger

> Thanks in advance!
> Justin
>
> _______________________________________________
> 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