On Wed, 27 Sep 2006, Horacio Samaniego wrote:
> I am unsure on how to deal with this... (this is usually easy on
> grass), however cuz all me figs have been done in R I need to be
> consistent.
>
> The question is how to to get a contour plot from a
> SpatialPixelsDataFrame.
>
> So far I have generated I seem to be succesfully generating the plot
> using :
> > contour(seq(-2423411.1,271933.9,length=674),seq
> (248129.5,3239402.6,length=748),matrix([EMAIL PROTECTED],ncol=748))
>
> but the plot seem to be upside down. It looks ok, but wen adding the
> map lines with :
> > plot(usaca,add=T)
>
> I notice that only the 'y' axis is shifted.... a transformation of
> the matrix won't do the trick. So, I wonder is what the best
> approach is for this. I tried making an image of it, but thinking
> that as.image.SpatialGridDataFrame will create a usable matrix don't
> seem to be quite right
>
No, because it creates the input list of x, y, z used by image() and
contour - the z component is the matrix.
> anyhow, I hope that some more experienced user will be able to tell
> me the correct way to do this,
>
> thanks,
>
It's not hard (from the example for image.SpatialGridDataFrame):
data(meuse.grid)
coordinates(meuse.grid) = c("x", "y")
gridded(meuse.grid) = TRUE
class(meuse.grid) # is a "SpatialPixelsDataFrame"
xyz <- as.image.SpatialGridDataFrame(meuse.grid["dist"]) # choose the
# variable you need
image(meuse.grid["dist"], axes=TRUE)
contour(xyz, add=TRUE)
(if you just do contour() on the matrix, the coordinates and aspect get
blown away) and if you want the contours as a SpatialLinesDataFrame:
SLDF <- contourLines2SLDF(contourLines(xyz))
image(meuse.grid["dist"], axes=TRUE)
plot(SLDF, add=TRUE)
Roger
>
> PD: here is the definition of my sp object:
>
> > str(grPC)
> Formal class 'SpatialPixelsDataFrame' [package "sp"] with 7 slots
> ..@ data :Formal class 'AttributeList' [package "sp"] with 1
> slots
> .. .. ..@ att:List of 6
> .. .. .. ..$ PC1: num [1:504152] 0.299 0.301 0.302 0.303 0.305 ...
> .. .. .. ..$ PC2: num [1:504152] -0.218 -0.219 -0.220 -0.220
> -0.221 ...
> .. .. .. ..$ PC3: num [1:504152] -0.0222 -0.0226 -0.0230 -0.0233
> -0.0237 ...
> .. .. .. ..$ PC4: num [1:504152] -0.0290 -0.0288 -0.0286 -0.0285
> -0.0283 ...
> .. .. .. ..$ PC5: num [1:504152] 0.0607 0.0608 0.0609 0.0610
> 0.0611 ...
> .. .. .. ..$ PC6: num [1:504152] 0.0681 0.0683 0.0685 0.0687
> 0.0688 ...
> ..@ coords.nrs : num(0)
> ..@ grid :Formal class 'GridTopology' [package "sp"] with 3
> slots
> .. .. ..@ cellcentre.offset: Named num [1:2] -2421412 250129
> .. .. .. ..- attr(*, "names")= chr [1:2] "s1" "s2"
> .. .. ..@ cellsize : Named num [1:2] 3999 3999
> .. .. .. ..- attr(*, "names")= chr [1:2] "s1" "s2"
> .. .. ..@ cells.dim : Named int [1:2] 674 748
> .. .. .. ..- attr(*, "names")= chr [1:2] "s1" "s2"
> ..@ grid.index : int [1:504152] 1 2 3 4 5 6 7 8 9 10 ...
> ..@ coords : num [1:504152, 1:2] -2421412 -2417413 -2413414
> -2409414 -2405415 ...
> .. ..- attr(*, "dimnames")=List of 2
> .. .. ..$ : NULL
> .. .. ..$ : chr [1:2] "s1" "s2"
> ..@ bbox : num [1:2, 1:2] -2423411 248130 271934 3239403
> .. ..- attr(*, "dimnames")=List of 2
> .. .. ..$ : chr [1:2] "s1" "s2"
> .. .. ..$ : chr [1:2] "min" "max"
> ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
> .. .. ..@ projargs: chr NA
>
> --
> Horacio Samaniego
> Dept. Biology
> University of New Mexico
> Albuquerque 87106, NM
>
> http://www.unm.edu/~horacio
>
>
>
>
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>
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--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: [EMAIL PROTECTED]
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