[R-sig-Geo] Apparent rotation when plotting a SpatialGridDataFrame?

[MacQueen, Don]

Thank you, Roger.

I see that in essence I separated my coords from my data,
in effect re-ordered the coords by making a grid topology,
and then rejoined the coords with the data in the original
order.

-Don

-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 10/1/12 11:45 AM, "Roger Bivand" <Roger.Bivand at nhh.no> wrote:

>On Mon, 1 Oct 2012, MacQueen, Don wrote:
>
>>
>> I have simple data coming to me from an outside source.
>> x,y are coordinates in a UTM projection, and z is a
>> measured value at each location.
>>
>> I make a SpatialPointsDataFrame from it, plot it with spplot(),
>> and it appears as expected.
>>
>> I convert to a SpatialGridDataFrame, plot using spplot(),
>> it appears to have been rotated 90 degrees.
>>
>> See example code to illustrate below.
>>
>> Am I doing something wrong?
>>
>
>No, this is a consequence of code cleanup, revision 1140 in R-forge SVN:
>
>https://r-forge.r-project.org/scm/viewvc.php/pkg/sp/R/Class-SpatialGrid.R?
>root=rspatial&r1=1140&r2=1204
>
>removing "coords" and "grid.index" slots from the definition of
>the SpatialGrid class. This split SpatialPixels and SpatialGrid cleanly,
>but meant that you can't smuggle the data slot across unpunished. This
>works:
>
>slot(tstsp, "data")$z
>tstpxdf <- as(tstsp, "SpatialPixelsDataFrame")
>slot(tstpxdf, "data")$z
>tstgrdf <- as(tstpxdf, "SpatialGridDataFrame")
>slot(tstgrdf, "data")$z # showing the re-ordering
>tmppl4 <- spplot(tstgrdf)
>print(tmppl4)
>
>
>Hope this helps,
>
>Roger
>
>>
>> I used the same sequence of conversions about 7 months ago on
>> a different set of data and did not see this problem. Inspecting
>> the two versions of the data does not suggest a problem with
>> the conversion process. The bounding box is consistent before
>> and after the conversion.
>>
>> Here is a simple example to illustrate, followed by sessionInfo()
>> It should be possible to just source the example code into an
>> R session.
>>
>> ##
>> ## simple example to illustrate the question
>> ##
>> require(sp)
>>
>> ## example data
>> tstdf <- expand.grid(x=1:3, y=1:3)
>> tstdf$z <- 5
>> tstdf$z[tstdf$x==tstdf$y] <- 10
>>
>> ## move points to somewhere actually in the zone
>> tstdf$x <- tstdf$x +  608000
>> tstdf$y <- tstdf$y + 4167900
>>
>> ## convert to spatial points data frame; UTM projection
>> tstsp <- tstdf
>> coordinates(tstsp) <- c('x','y')
>> proj4string(tstsp) <- CRS('+init=epsg:32610')
>> print(bbox(tstsp))
>>
>> ## plot
>> tmppl1 <- spplot(tstsp)
>> print(tmppl1)
>>
>>
>> ## convert to spatial grid
>> tstgr <- points2grid(tstsp)
>> tstsgr <- SpatialGrid(tstgr,
>>             proj4string=CRS('+init=epsg:32610'))
>> print(bbox(tstsgr))
>> tstsgrd <- SpatialGridDataFrame(tstgr,
>>                data=tstsp at data,
>>                proj4string=CRS('+init=epsg:32610'))
>> print(bbox(tstsgrd))
>>
>> ## plot -- compare with first plot
>> tmppl2 <- spplot(tstsgrd)
>> print(tmppl2)
>>
>> ##
>> ## sessionInfo()
>> ##
>> R version 2.15.1 (2012-06-22)
>> Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
>>
>> locale:
>> [1] C
>>
>> attached base packages:
>> [1] stats     graphics  grDevices utils     datasets  methods   base
>>
>> other attached packages:
>> [1] sp_1.0-0
>>
>> loaded via a namespace (and not attached):
>> [1] grid_2.15.1    lattice_0.20-6
>>
>>
>> -------------------------------
>> By the way, the reason for converting to a spatial grid is
>> so that I can then convert it to a SpatialPolygonsDataFrame,
>> spTransform() to long/lat and export to KML,
>> then display in GoogleEarth with a raster-like appearance.
>>
>>
>> There are no doubt other and likely better ways to accomplish
>> the same end goal, a raster-like display in GoogleEarth,
>> but this is a way I found.
>> --------------------------------
>>
>>
>
>-- 
>Roger Bivand
>Department of Economics, NHH Norwegian School of Economics,
>Helleveien 30, N-5045 Bergen, Norway.
>voice: +47 55 95 93 55; fax +47 55 95 95 43
>e-mail: Roger.Bivand at nhh.no
>