SpatialGrid from matrix

object.size(g)

object.size(x)

Michael Sumner wrote:

require(splancs)
data(bodmin)
x= kernel2d(as.points(bodmin), bodmin$poly, h0=2, nx=100, ny=100)
require(sp)
g=expand.grid(x$x,x$y,x$z)

The last line gives the following error:
Error: cannot allocate vector of size 390625 Kb

You are expanding your grid for every cell in the matrix, per every grid
location - which *really is* a lot of memory.  You really want something
like this:

g <- cbind(expand.grid(x = x$x, y = x$y), as.vector(x$z))
coordinates(g) <- c("x", "y")
gridded(g) <- TRUE
image(g)
contour(x, add = T)  ## just to be sure

I'm pretty sure the ordering is right for this case, but be sure to check.

Cheers, Mike.

Thanks, Mike, that's an excellent solution.

In this way g is of

class(g)

[1] "SpatialPixelsDataFrame"
attr(,"package")
[1] "sp"

meaning that it stores x and y coordinates. To save this
space, you could store it as SpatialGridDataFrame:

object.size(g)

[1] 283528

fullgrid(g)=T
object.size(g)

[1] 83476

class(g)

[1] "SpatialGridDataFrame"
attr(,"package")
[1] "sp"

A direct way to create a SpatialGridDataFrame without
using expand.grid() would use GridTopology() and
SpatialGridDataFrame(). You'd have to reorder x$z
for that, too.
--
Edzer