On Sat, 29 May 2010, Agustin Lobo wrote:
Why do I have to use proj4string() instead of projection() in this example?
You are getting mixed up between packages. projection() is a function in
the raster package, while proj4string() is a function in sp. Use
projection() for classes defined or extended in raster, proj4string() for
classes defined in sp. Critically, projection<-() tries to assign to a
slot called "crs", which is not present in Spatial* objects.
My feeling is that the sp nomenclature is clearer but clunkier, because it
specifies the representation of the projection as a PROJ.4 string, while
the name of the function "projection" could admit arbitrary
representations, but in fact uses the same representation and mechanisms
as sp (with verification through the PROJ.4 library if rgdal is loaded).
Probably projection<-() needs the same if() statement as that used in
projection(), to distinguish extensions of "BasicRaster" from those of
"Spatial", in which case projection<-() and proj4string<-() will both work
on objects extending "Spatial" too.
Roger
class(Montseny20090409sh)
[1] "SpatialPointsDataFrame"
attr(,"package")
[1] "sp"
projection(Montseny20090409sh)
[1] "+proj=utm +zone=31 +ellps=intl +units=m +no_defs"
a<- SpatialPoints(coordinates(Montseny20090409sh))
class(a)
[1] "SpatialPoints"
attr(,"package")
[1] "sp"
projection(a) <- projection(Montseny20090409sh)
Error in checkSlotAssignment(object, name, value) :
"crs" is not a slot in class "SpatialPoints"
Calls: projection<- -> @<- -> slot<- -> checkSlotAssignment
proj4string(a) <- projection(Montseny20090409sh)
geogWGS84 <- CRS("+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs")
aGW <- spTransform(a, geogWGS84)
Montseny20090409sh2 <- Montseny20090409sh
montseny20090409...@data <- cbind(montseny20090409...@data,coordinates(aGW))
Thanks for any clarification,
Agus
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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.biv...@nhh.no
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