[R-sig-Geo] lat/long conversions to easting/northing

[Roger Bivand]

On Thu, 15 May 2008, Sylvia Churcher wrote:

> Hello all,
>
> I have a set of sample sites described in latitude and longitude and I'd 
> like to convert them to easting and northing for use in the kriging 
> technique.
>
> I'm a little surprised that I need to do this conversion...is there 
> perhaps another R package that works with lat and long coordinates in 
> spatial analysis?

Both fields (Krig) and gstat (gstat and predict.gstat) include 
possibilities for interpolating using geographical coordinates. However, 
unless your study area is truly continental, you may well do better to 
project to the plane (see spTransform methods in the rgdal package).

If you are near a break in geographical coordinates (-/+180 degrees or 
0/360 degrees), you may find that great circle distances break down. I've 
found - for example, that Polar Stereographic seems to do better for the 
Arctic than trying to use geographical coordinates. Including trends also 
becomes a problem, by the way.

Roger

>
> Any help with either question is much appreciated!
>
> Many thanks,
>
> S. Churcher
>
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-- 
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