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

From: Paul Hiemstra <p.hiemstra_at_geo.uu.nl>
Date: Tue, 01 Jul 2008 10:34:53 +0200

The r-sig-geo mailing list is a better forum for your kind of questions, you are much more likely to get good answers.

cheers,
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=""))
>
> Regards,
> Jan
>
> Ps. Is this good approach to plot satellite images as spatial grids in
> R? is rgdal an better approach?
>
> ______________________________________________
> R-help_at_r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.
>

```--
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone: 	+31302535773
Fax:	+31302531145
http://intamap.geo.uu.nl/~paul

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