[GRASS-stats] Scatterplot "thinning" (points reduction)?

[Markus Neteler]

Hi Dylan,

On Sun, Aug 16, 2009 at 8:02 PM, Dylan
Beaudette<dylan.beaudette at gmail.com> wrote:
> Hi Markus,
>
> Can you sample the original maps with v.random + v.what.rast first?

This gave me the idea: spsample() - I just read page 118 in "Applied
spatial data analysis with R" (great book, http://www.asdar-book.org/ !).

But apparently I am missing something... (I am certainly reading too fast):

# Spearfish example
> mydata <- readRAST6(c("elevation.dem","soils"))
> subdata <- spsample(mydata, 500, type= "random")

Looks good but...

> str(subdata)
Formal class 'SpatialPoints' [package "sp"] with 3 slots
  ..@ coords     : num [1:497, 1:2] 600572 596804 599446 597732 600336 ...
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : NULL
  .. .. ..$ : chr [1:2] "x" "y"
  ..@ bbox       : num [1:2, 1:2] 590022 4914167 608953 4927981
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : chr [1:2] "x" "y"
  .. .. ..$ : chr [1:2] "min" "max"
  ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
  .. .. ..@ projargs: chr " +proj=utm +zone=13 +a=6378206.4
+rf=294.9786982 +no_defs
+nadgrids=/home/neteler/grass65/dist.x86_64-unknown-linux-gnu/etc/nad"|
__truncated__

... where are the data?

The original looks like:
> str(mydata)
Formal class 'SpatialGridDataFrame' [package "sp"] with 6 slots
  ..@ data       :'data.frame': 2654802 obs. of  2 variables:
  .. ..$ elevation.dem: int [1:2654802] NA NA NA NA NA NA NA NA NA NA ...
  .. ..$ soils        : int [1:2654802] NA NA NA NA NA NA NA NA NA NA ...
  ..@ grid       :Formal class 'GridTopology' [package "sp"] with 3 slots
  .. .. ..@ cellcentre.offset: Named num [1:2] 590015 4914025
  .. .. .. ..- attr(*, "names")= chr [1:2] "x" "y"
  .. .. ..@ cellsize         : num [1:2] 10 10
  .. .. ..@ cells.dim        : int [1:2] 1899 1398
  ..@ grid.index : int(0)
  ..@ coords     : num [1:2, 1:2] 590015 608995 4914025 4927995
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : NULL
  .. .. ..$ : chr [1:2] "x" "y"
  ..@ bbox       : num [1:2, 1:2] 590010 4914020 609000 4928000
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : chr [1:2] "x" "y"
  .. .. ..$ : chr [1:2] "min" "max"
  ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
  .. .. ..@ projargs: chr " +proj=utm +zone=13 +a=6378206.4
+rf=294.9786982 +no_defs
+nadgrids=/home/neteler/grass65/dist.x86_64-unknown-linux-gnu/etc/nad"|
__truncated__

According to
showMethods("spsample")
grids are supported... I guess I am missing a trivial bit, might be
the time here...

thanks
Markus