[R-sig-Geo] spsample() ok with type= 'stratified', but gives error with 'random'

[Olsen.Tony at epamail.epa.gov]

You can also use the library spsurvey to do a random sample using a sp
object or ESRI  shapefile.  It handles polygons, lines, and point
spatial objects.  Does stratified, unequal probability, and spatial
balance.

Anthony (Tony) R. Olsen
AMB Branch Chief
USEPA NHEERL
Western Ecology Division
200 S.W. 35th Street
Corvallis, OR 97333
Voice: (541) 754-4790
Fax: (541) 754-4716
email: Olsen.Tony at epa.gov
ARM Web Page: http://www.epa.gov/nheerl/arm


                                                                        
             Don MacQueen                                               
             <macq at llnl.gov>                                            
             Sent by:                                                To 
             r-sig-geo-bounce         r-sig-geo at stat.math.ethz.ch       
             s at stat.math.ethz                                        cc 
             .ch                                                        
                                                                Subject 
                                      [R-sig-Geo] spsample()  ok with   
             06/07/2007 09:27         type= 'stratified', but gives     
             AM                       error with 'random'               
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        




I don't know enough to assess whether I have a misunderstanding or a
mistake.

spsample() with type='random' is giving an error, but succeeding with
type='stratified'.

Maybe random sampling requires projection information and stratified
doesn't?
I may have constructed my SpatialPolygonsDataFrame incorrectly?

Thanks
-Don

Details:

spgd consists of two rectangles, one inside the other, and the inside
one is a hole.
The outer one has vertices in counter-clockwise order; the inner one
in clockwise order.

>  class(tst)
[1] "SpatialPolygonsDataFrame"
attr(,"package")
[1] "sp"

>  summary(tst)
Object of class SpatialPolygonsDataFrame
Coordinates:
         min      max
r1 990396.8 990762.3
r2 213369.4 213702.6
Is projected: NA
proj4string : [NA]
Data attributes:
     ID
  zone:1


>  stst <- spsample(tst,type='stratified',n=50)
>  plot(tst)
>  points(stst)
>  stst <- spsample(tst,type='random',n=50)
Error in `proj4string<-`(`*tmp*`, value = <S4 object of class "CRS">) :
         proj4string only works for class(es extending) Spatial


##########
>  sessionInfo()
R version 2.5.0 (2007-04-23)
powerpc-apple-darwin8.9.1

locale:
C

attached base packages:
[1] "stats"     "graphics"  "grDevices" "utils"     "datasets"
"methods"   "base"

other attached packages:
maptools       sp  foreign    rmacq
"0.6-12" "0.9-14" "0.8-20"    "1.0"

##########
## since tst is fairly small, here it is:
##########
>  tst
An object of class "SpatialPolygonsDataFrame"
Slot "data":
        ID
zone zone

Slot "polygons":
[[1]]
An object of class "Polygons"
Slot "Polygons":
$zn
An object of class "Polygon"
Slot "labpt":
[1] 990579.4 213536.2

Slot "area":
[1] 64601.13

Slot "hole":
[1] FALSE

Slot "ringDir":
[1] 1

Slot "coords":
             x        y
[1,] 990499.3 213702.6
[2,] 990762.3 213559.8
[3,] 990658.2 213369.4
[4,] 990396.8 213513.2
[5,] 990499.3 213702.6


$zn2
An object of class "Polygon"
Slot "labpt":
[1] 990584.4 213537.3

Slot "area":
[1] 30367.20

Slot "hole":
[1] TRUE

Slot "ringDir":
[1] -1

Slot "coords":
             x        y
[1,] 990492.6 213650.8
[2,] 990441.8 213549.4
[3,] 990673.3 213423.7
[4,] 990728.1 213525.6
[5,] 990492.6 213650.8



Slot "plotOrder":
[1] 1 2

Slot "labpt":
[1] 990579.4 213536.2

Slot "ID":
[1] "zone"

Slot "area":
[1] 94968.33



Slot "plotOrder":
[1] 1

Slot "bbox":
         min      max
r1 990396.8 990762.3
r2 213369.4 213702.6

Slot "proj4string":
CRS arguments: NA

--
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA

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