-----Message d'origine----- De?: Roger Bivand [mailto:Roger.Bivand at nhh.no] Envoy??: 24 ao?t 2006 15:28 ??: Philippe Roy Cc?: r-sig-geo at stat.math.ethz.ch Objet?: Re: [R-sig-Geo] Mass conversions of Lat/Long to UTM (many zone)
On Thu, 24 Aug 2006, Philippe Roy wrote:
Hi everyone! I'm new to R. I'll try using it for some Kriging. My aim in the short-term is to convert my 2300 stations database from lat-long to UTM. This network of stations goes from Virginia to the south, to Montr?al to the north, east coast to Michigan in the west. So, I have a lot of UTM zones to consider. Reading the archives, I've seen this formula to calculate the zones, based on lat-long coordinates : UTM = floor((lon + 180) / 6) + 1 So, if I understand correctly, I need to run this formula on each station to get their zone, abnd then I use something like convUL ?
If you want to use all the stations together, then they must be in the same zone (otherwise the western edge of the zone will jump for stations in different zones). I think that for continental North America a central UTM zone will not be a very good idea, and that probably a Lambert Azimuthal Equal Area is a better choice. You can then use project() or spTransform() in the rgdal package, for example, with EPSG code 2163: US National Atlas Equal Area +proj=laea +lat_0=45 +lon_0=-100 +x_0=0 +y_0=0 +a=6370997 +b=6370997 +units=m with some modification of +lat_0 and +lon_0 to suit your region.
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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 Ok, so, in my kriging code, I need to specify a maximum distance in km (or meter can't remember). Is this Lambert Azimuthal Equal Area good for Euclidian distance? I mean, I need to specify the maximum distance to consider a station or not for each grid point of my regular grid. Would that be good then? Sorry if it sounds non-understandable! :/