[R-sig-Geo] Converting shapefile from gridded to lat/ lng

[Pascal Oettli]

Hello,

Thank you Barry. Always interesting to learn something.

Regards,
Pascal


On 20 January 2014 17:25, Barry Rowlingson <b.rowlingson at lancaster.ac.uk> wrote:
> On Mon, Jan 20, 2014 at 8:10 AM, Pascal Oettli <kridox at ymail.com> wrote:
>
>> crs.ll <- "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0"
>> crs.tmerc <- "+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717
>> +x_0=400000 +y_0=-100000 +ellps=airy +datum=OSGB36 +units=m +no_defs"
>>
>> authoritiesMap.TMERC <- readShapePoly("LAD_Pop_EngWales2011",
>> proj4string=CRS(crs.tmerc))
>
> proj4string(authorities.Map) = CRS(crs.tmerc) # surely?
>
>> authoritiesMap.LL <- spTransform(authoritiesMap.TMERC, CRS(crs.ll))
>
> If you use readOGR from package:rgdal *and* your shapefile comes with
> the correct .prj file (in the same folder with the .shp and .dbf) then
> the spatial polygons object will already have the correct CRS assigned
> to it and you can skip half these steps. Something like:
>
> map = readOGR(".","LAD_Pop_EngWales2011")
> mapLL = spTransform(map, CRS("+init=epsg:4326"))
>
>  - epsg code 4326 is the lat-long system as used by GPS. epsg code
> 27700 is the UK national grid format which might be what you original
> file is, or something else entirely! Anyway, if you've got a .prj
> file, its a two-liner.



-- 
Pascal Oettli
Project Scientist
JAMSTEC
Yokohama, Japan