proj4string-issue - leading spaces

On Fri, 11 Jan 2013, Edzer Pebesma wrote:

On 01/11/2013 12:10 PM, Jon Olav Skoien wrote:

Is there a simple way to solve this, not having check and modify the
proj4string of all objects? Or could the call to identical in functions
like over be replaced by an identicalCRS()-function?

identicalCRS = function(x,y) {
  identical(CRS(proj4string(x)), CRS(proj4string(y)))
}

Great suggestion, Jon; I added this to sp on r-forge.

Not so great, it doesn't address the problem that users with different 
versions of rgdal (and/or with stored objects from older versions of 
rgdal) may have extraneous prepended spaces. The function nees to test 
for NA or not, then length, if lengths equal, OK, test, if differ by 
one check whether space and if so trim, ...

You mean that the suggestion does not solve the problem when using CRS 
from sp instead of rgdal as the sp-version does not trim leading spaces? 
Then I think an alternative sp version could use gsub without being too 
complicated. Leading spaces can be removed from the proj4string if they 
exists, NAs are not touched:

ch = "+init=epsg:4326"
gsub("^ .", "", ch)
ch = " +init=epsg:4326"
gsub("^ .", "", ch)
ch = NA
gsub("^ .", "", ch)

and the function could be something like:

identicalCRS = function(x,y) {
   if (inherits(x, "Spatial")) x = proj4string(x)
   if (inherits(y, "Spatial")) y = proj4string(y)
   x = gsub("^ .", "", y)
   y = gsub("^ .", "", y)
   identical(x,y)
}

Two NA-proj4strings will be treated as identical, same as they are now. 
However, it will not catch the similarity between "+init=epsg:4326" and 
"+init=epsg:4326 +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs 
+towgs84=0,0,0" such as a possible rgdal-version (first suggestion 
above) can do.

Cheers,
Jon

Jon Olav Sk?ien
Joint Research Centre - European Commission
Institute for Environment and Sustainability (IES)
Land Resource Management Unit

Via Fermi 2749, TP 440,  I-21027 Ispra (VA), ITALY

jon.skoien at jrc.ec.europa.eu
Tel:  +39 0332 789206

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