[R] Are centre coordinates or upper left corners used of x, y for SpatialPixels?

[Paul Hiemstra]

Hi Jan,

In response to your ps. I think using rgdal is the best way to go. If 
your data is for example in a GeoTIFF file, reading it is as simple as:

GRID = readGDAL("your_file.tif")

Saves you some hassel and a number of lines of code.

cheers and hth,
Paul

Jan.Verbesselt at csiro.au wrote:
> Dear all,
>
> I'm working with satellite images in R and plotting them via the code
> below.
> I was wondering whether coordinates (spatial["x"], spatial["y"]) are
> used as centre coordinates of the pixels in the GRID? In this script;
> spatial["x"] & spatial["y"] are the centre coordinates of the satellite
> image pixels. I'm asking this because some software packages use the
> upper left corner of a pixel as a reference.
>
> require(sp)
>   # --> Create GRID and image in R
>    S <- SpatialPoints(cbind(spatial["x"], spatial["y"]), proj4string =
> proj)
>     SP <- SpatialPixels(S, proj4string = proj, tolerance = 5e-07)
>     GRID <- SpatialPixelsDataFrame(points = SP , tolerance = 5e-07, data
> = spatial[columnname])
>     proj4string(GRID) <- proj
>     gridded(GRID)
>     
>     nr <- 30
>     zaxis <- c(0.7, 1)
>     plot(as(GRID, "Spatial"), axes=T)
>     title(main = paste(" Day ",dy[i,1], " Year ",dy[i,2], sep=""))
>     image(GRID, zlim=zaxis, col=rainbow(nr,start=0, end=2/6),add=T)
>
> Thanks for your help,
> Regards,
> Jan
>
> Ps. Is this good approach to plot satellite images as spatial grids in
> R? is rgdal an better approach?
>
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-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
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