[R] Easting and northing cf. Latitude and longitude

[Roger Bivand]

On Fri, 22 Jun 2001, Patrick Connolly wrote:

> I think I've seen this discussed here before but it doesn't seem to
> appear in the archive.

In r-help, 20 April 2001.

> 
> I am using the map package which so far has been fine for my purposes.
> Some people I work with have GPS type data that defines positions as
> number of metres not degrees.  I don't know how much the system
> varies, but in New Zealand, they are referred to as Eastings and
> Northings.
> 

The answer I gave then - there were others - see the archives - was:

One good source is http://www.remotesensing.org/proj/ for the PROJ.4
software. Another is the mapproject program in GMT at
http://gmt.soest.hawaii.edu/. These are both external to R, but it seems
likely that PROJ.4 will form part of an R map package at some stage. You
didn't say which platform you use - both these are native Unix/Linux, but
at least GMT is available for NT too. While it would be possible to write
R code to do this, both of these sources are well-tried and so more likely
to work as expected.

I feel that roll-your-own is not necessarily a good solution - map
projection is numerically sensitive, especially when dealing with lots of
significant digits in decimal degrees. The sources here also assume that
you know about the parameters for your projection - as was already pointed
out.

Roger

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no
and: Department of Geography and Regional Development, University of
Gdansk, al. Mar. J. Pilsudskiego 46, PL-81 378 Gdynia, Poland.



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