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adding ids and df to hexagonal polys ?

5 messages · Roger Bivand, Horacio Samaniego

Original
Horacio Samaniego
# 
Hi, 

I am trying to understand the different data types in the sp package.
However, I do not seem to get the way that spdf are built. 

For example, let say that I can build a hexagonal grid. That work just
fine using
I'm unclear about adding a df with IDs to this new SpetialPolygons class

I guess that I'm not understanding how ids are assigned... any hint
would be appreciated

thanks
Roger Bivand
#
On Wed, 9 Sep 2009, Horacio Samaniego wrote:

            

      
      
      
    

        
library(maptools)
xx <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1],
  IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66"))
hpts <- spsample(xx, type="hexagonal", n=100)
hpoly <- HexPoints2SpatialPolygons(hpts)
o <- overlay(xx, hpts)
row.names(o) <- row.names(hpoly)
hpoly1 <- SpatialPolygonsDataFrame(hpoly, data=o)
summary(hpoly1)
spplot(hpoly1, "BIR74")

After making sure that the IDs agree, just use the constructor for
SpatialPolygonsDataFrame objects.

Hope this helps,

Roger

            

      
      
      
    

        

      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Horacio Samaniego
    

    

      
      #
    

  


  

      
Thanks for the hints here... but I'm guessing that there's somethings
missing...

the 5th command line (row.names(o) <- row.names(hpoly)) does not make
sense to me as hpoly is a spatialPolygon which has no row names

            

      
      
      
    

        
Formal class 'SpatialPolygons' [package "sp"] with 4 slots
  ..@ polygons   :List of 965
  ..@ plotOrder  : int [1:965] 1 2 3 4 5 6 7 8 9 10 ...
  ..@ bbox       : num [1:2, 1:2] 446230 3778428 1331230 8047934
  .. ..- attr(*, "dimnames")=List of 2
  ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots

            

      
      
      
    

        
Length  Class   Mode 
     0   NULL   NULL 

I thought, perhaps there's a spelling problem? but no...

            

      
      
      
    

        
Error in SpatialPolygonsDataFrame(hpoly, data = o) : 
  row.names of data and Polygons IDs do not match

How is this possible?


So I tried a "brute force" approach, with no success

            

      
      
      
    

        
Error in `rownames<-`(x, value) : 
  attempt to set rownames on object with no dimensions

I seem to have the concept wrong to begin with here. How are IDs
assigned to a 'SpatialPolygons' class? I should be able to assign them
regardless of the template shape used, right? Which would make the
overlay() step unnecessary?


I guess that I need some clarification on how the class is built..
my apologies if it's too obvious of a  question... I just hope not to be
the only one missing this
 thanks

        
On Thu, 2009-09-10 at 09:22 +0200, Roger Bivand wrote:

            

      
      
      
    

        

      
      
    

            

      
      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Roger Bivand
    

    

      
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On Thu, 10 Sep 2009, Horacio Samaniego wrote:

        

            

      
      
      
    

        
The overlay() step was just for illustration. Spatial* objects may have 
row.names() methods, but they are not row.names()<- methods. Look for 
spChFIDs() methods in maptools for changing or assigning IDs. However, the 
hexagon polygons do have IDs, just look at them (assuming you have a 
recent sp - you do update regularly?).

Roger

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Horacio Samaniego
    

    

      
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Thanks a lot Roger, I had overlooked spChFIDs()

I just run the packages off the repositories in ubuntu jaunty

I have sp = 2.8.1

it seem to be an old version with no rownames for my hexagon polys...
however, this an easy fix.

            

      
      
      
    

        
spChFIDs(hpoly,as.character(1:length(slot(hpoly,"polygons"))))

did the trick and I now understand better how to create hexagonal
polys, 

thanks again!!

        
On Thu, 2009-09-10 at 18:19 +0200, Roger Bivand wrote: