On 05/06/2010 07:26 AM, Robert J. Hijmans wrote:
> Seth,
> I think I overlooked what is perhaps the easiest way to do this, using
> a standard replacement approach:
>
> library(raster)
> r <- raster(system.file("external/test.grd", package="raster"))
> p1a <- rep(100, ncol(r))
> r[1:ncol(r)] <- p1a
> r <- writeRaster(r, filename='test.rst', overwrite=TRUE)
> plot(r)
Please note that in order to get the usual map view for this data set,
such that 1 km NS equals 1 km EW, you need to add:
plot(r, asp=1)
> Robert
>
>
> On Wed, May 5, 2010 at 10:05 PM, Robert J. Hijmans <r.hijm...@gmail.com>
> wrote:
>> 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
>>> _______________________________________________
>>> R-sig-Geo mailing list
>>> R-sig-Geo@stat.math.ethz.ch
>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>
>>
>
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--
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics e.pebe...@wwu.de
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