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

From: <Jan.Verbesselt_at_csiro.au>
Date: Tue, 01 Jul 2008 18:03:59 +1000


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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