[R-sig-Geo] Creating a spatial grid from table and x & y break vectors?

[Michael Sumner]

If image(gridData) works, then image(xbrks, ybrks, gridData) should
work as well, and plot with the correct spatial coordinates - this
assumes that xbrks and ybrks correspond to the dimensions of gridData
- either exactly (the centres) or longer by one element (the corners).

In the sp package you can do x <-  image2Grid(list(x = xbrks, y =
ybrks, z = gridData)) to get a SpatialGridDataFrame, and then with
maptools you can easily convert to spatstat's "im":

library(maptools)
x.im <- as.im(x)

Either of those will help to plot or image() the data in the proper
space and overplot points.

Cheers, Mike.

On Thu, Mar 31, 2011 at 2:21 PM,  <stepen.condors at gmail.com> wrote:
> Hi all,
> I have the following datasets and am trying to generate a spatial grid which can be plotted (somewhat like the object created by spatstat's quadratcount):
>
> Dataset 1: A table containing a known number of cells, each value relating to the intensity at a given cell.
>
>> str(gridData)
>  table [1:250, 1:400] 0 0 0 0 0 0 1.72 0 0 0 ...
>  - attr(*, "dimnames")=List of 2
>  ..$ : chr [1:250] "A" "B" "C" "D" ...
>  ..$ : chr [1:400] "A" "B" "C" "D" ...
>
> Datasets 2&3: vectors of xbreaks and ybreaks - specifying the eastings and northings of the grid cells I want to plot.
>
>> str(xbrks)
>  num [1:401] 1740000 1740100 1740200 1740300 1740400 ...
>
>> str(ybrks)
>  num [1:251] 5420000 5420100 5420200 5420300 5420400 ...
>
>
> Given these three datatsets, what would be the easiest way to turn this into a plottable (spatially located) grid, that I can then overlay ppp onto?
>
> I am aware that I can simply plot the table as an image, but obviously this is not spatially referenced in anyway so I wouldn't then be able to overlay a point data set and allow the pts and grid polygons to interact.
>
> Any assistance is greatly appreciated.
> Stepen
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-- 
Michael Sumner
Institute for Marine and Antarctic Studies, University of Tasmania
Hobart, Australia
e-mail: mdsumner at gmail.com