Dear Seth,
I think the problem is that you try to overwrite values in an existing
file. That is not directly possible (with raster anyway). You have to
start a new fil. Below are some examples. Also see
vignette('functions', 'raster')
#1 if you can read the whole raster into memory
p1a <- rep(0, ncol(rout))
rin <- raster(system.file("external/test.grd", package="raster"), values=TRUE)
rin[1:ncol(rin)] = p1a
rout <- writeRaster(rin, filename="write1.rst", format="IDRISI",overwrite=TRUE)
#2 row by row (and slow)
rin <- raster(system.file("external/test.grd", package="raster"))
rout <- raster(rin)
p1a <- rep(0, ncol(rout))
rout <- setValues(rout, p1a, 1)
rout <- writeRaster(rout, filename="write2.rst", format="IDRISI",overwrite=TRUE)
for (r in 2:nrow(rout)) {
rin <- readRow(rin, r)
rout <-setValues(rout, values(rin), r)
rout <- writeRaster(rout, filename="write5.rst",
format="IDRISI",overwrite=TRUE)
}
# 3 block by block (much faster); using the rgdal driver
(format='RST') so that you
# first copy all values and then overwrite rows at any location
rin <- raster(system.file("external/test.grd", package="raster"))
rout <- raster(rin)
bs <- blockSize(rout)
rout <- writeStart(rout, filename="write3.rst", format="RST", overwrite=TRUE)
for (i in 1:bs$n) {
v = getValuesBlock(rin, row=bs$row[i], nrows=bs$size)
writeValues(rout, v, bs$row[i])
}
p1a <- rep(0, ncol(rout))
writeValues(rout, p1a, 1) # replace a row
rout <- writeStop(rout)
Robert
On Wed, May 5, 2010 at 6:52 PM, Seth J Myers <sjmy...@syr.edu> wrote:
> Hi,
>
> I'm running R 2.11.0 on a 32 bit Windows Vista machine. I have new versions
> of all relevant libraries installed. I have been reading from IDRISI .rst
> files and this works fine using raster() and getValues(). I have passed the
> values from the .rst files through another R object and would like to write
> them as an .rst file. In the following code, I am attempting to set the 1st
> row values of a RasterLayer object and then write these to a .rst file. All
> raster files I am working with have 3,700 columns and 4,203 rows and are
> Connecticut StatePlane coordinate system which is equivalent to lambert's
> conformal conic proj.
>
> #extract 2nd column of a matrix which are the values of interest for the 1st
> row
> p1a<-p1[c(1:3700),c(2)]
> p1am<-as.matrix(p1a)
> #create RasterLayer object from a .rst file that was created in IDRISI
> beforehand with all 0s (real nums) for cell values
> put<-raster("C:\\rforest\\data\\rst85\\write2.rst",values=FALSE)
> #set 1st row to equal the values of interest
> put<-setValues(put,p1am,1)
> #write to a .rst file that I created in IDRISI beforehand with all 0s (real
> nums)
> writeRaster(put, filename="C:\\rforest\\data\\rst85\\write5.rst",
> format="IDRISI",overwrite=TRUE)
>
>
> PROBLEM:
>
> Until the writeRaster function call, everything is working. I can use
> getValues to look at the 1st row of "put", and this equals p1am values. I
> can look at the 2nd row of "put" and they are all zeros. The writeRaster
> function does not give an error but, when opened in IDRISI, the legend seems
> correct but the values are expressed in scientific notation and are MUCH too
> small. Also, the 1st row values are copied for all rows, when I expect all
> but row=1 to be equal to 0. I tried, prior to opening in IDRISI, to create a
> RasterLayer object from the output raster from writeRaster above, to see if R
> gives the result wanted. This results in the following error message and
> report on the RasterLayer object created.
>
>> put2<-raster("C:\\rforest\\data\\rst85\\write5.rst",values=TRUE)
>> put3<-getValues(put2,1)
> Error:
> GDAL Error 3: Can't read(C:\rforest\data\rst85\write5.rst) block with
> X offset 0 and Y offset 0.
> No error
> Error in values(readRows(x, row, nrows)) :
> error in evaluating the argument 'x' in selecting a method for function
> 'values'
>> put2
> class : RasterLayer
> filename : C:\rforest\data\rst85\write5.rst
> nrow : 4203
> ncol : 3700
> ncell : 15551100
> min value : 0
> max value : 0
> projection : +proj=lcc +lat_1=41.86666666666667 +lat_2=41.2
> +lat_0=40.83333333333334 +lon_0=-72.75 +x_0=304800.6096 +y_0=152400.3048
> +ellps=GRS80 +datum=NAD83 +units=m +no_defs +towgs84=0,0,0
> xmin : 221895.5
> xmax : 334671.7
> ymin : 164342.4
> ymax : 292450.1
> xres : 30.48006
> yres : 30.48006
>
>
> I have tried this entire process starting NOT with blank 0 rasters to create
> my SpatialLayer object (a shortcut I thought may be a problem) but instead
> creating rasters by specifying projections etc on non-used filenames. The
> results are the same.
>
> Thanks,
> Seth
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>
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