[R-sig-Geo] reading *.grd files - revisited

[Monica Pisica]

Hi Robert,
 
Thank you so much for your help. It works very nicely .... i wonder why the extension was grd .... nowhere on the site from where i downloaded the data it said it is a netCDF file .... 
 
Monica


> Date: Wed, 28 Jan 2009 09:58:23 +0800
> Subject: Re: [R-sig-Geo] reading *.grd files - revisited
> From: r.hijmans at gmail.com
> To: pisicandru at hotmail.com
> CC: r-sig-geo at stat.math.ethz.ch
> 
> Dear Monica,
> 
> You probably refer to this thread:
> https://stat.ethz.ch/pipermail/r-sig-geo/2008-October/004326.html
> which is about Surfer (.grd) files. Unfortunately .grd is used for
> many different formats, and your file is not a Surfer .grd file.
> 
> In fact it is a netCDF file. ( .cdf or .nc are more common extensions
> for that format !)
> 
> I was able to read your file and plot the values like this (I use the
> raster package, but you can adapt the last bit if you do not want
> that):
> 
> # you probably need to install these two packages:
> install.packages("ncdf")
> install.packages("raster", repos="http://R-Forge.R-project.org")
> 
> require(ncdf)
> require(raster)
> 
> f <- "d:/test_grid.grd"
> nc <- open.ncdf(f)
> xr <- get.var.ncdf(nc, nc$var[[1]])
> yr <- get.var.ncdf(nc, nc$var[[2]])
> res <- get.var.ncdf(nc, nc$var[[4]])
> dims <- get.var.ncdf(nc, nc$var[[5]])
> v <- as.vector(get.var.ncdf(nc, nc$var[[6]]))
> close.ncdf(nc)
> 
> xm <- xr[1] - 0.5 * res[1]
> xx <- xr[2] + 0.5 * res[1]
> ym <- yr[1] - 0.5 * res[2]
> yx <- yr[2] + 0.5 * res[2]
> 
> r <- newRaster(xmn=xm, xmx=xx, ymn=ym, ymx=yx, ncols=dims[1], nrows=dims[2])
> r <- setValues(r, v)
> plot(r)
> 
> # if you want an sp grid object
> sp <- asSpGrid(r)
> 
> 
> Robert
> 
> On Wed, Jan 28, 2009 at 12:21 AM, Monica Pisica  wrote:
>>
>> Hi,
>>
>> I've read already the thread about how to read *.grd files in R. What i want to do is to re-save the file in a geotiff format so i can load it in ArcGIS. I tried readRGDAL and i got the following error:
>>
>> x <- readRGDAL("test_grid.grd")
>> Error in .local(.Object, ....):
>> GDAL Error 4: "test_grid.grd' not recognized as a suported file format.
>>
>> Next step was to do what Alexander Brenning suggested using RSAGA but after installing the library and trying the following command i got this error:
>>
>> rsaga.get.usage("io_grid",3)
>>
>> Error in setwd (env$workspace) : character argument expected
>> In addition: warning message:
>> In rsaga.env()
>> SAGA command line program 'saga.cmd.exe' not found in any of the paths
>> c:/PROGRA~2/R/R~28~1.1PA/library/RSAGA/saga_vc
>> .....
>>
>> Following afterwards a list of directories in my computer. Do i need to install any other additional package and load it in order to use RSAGA???
>>
>> I receive almost same error for the command
>> rsaga.geoprocessor("io_grid",3, param = list(GRID = "temp.sgrd", FILE = "test_grid.grd"))
>>
>> I have installed R 2.8.1 patched and all packages are updated, on a Windows XP professional x64 machine 64 bit.
>>
>> If anybody wants to give it a try you will find the file (probably around noon - it takes about 15 - 30 min to upload on the site) at ftp://stpfiles.er.usgs.gov/Monica/GRID/test_grid.grd
>>
>> Thanks for all the help,
>>
>> Monica
>> _________________________________________________________________
>>
>>
>> 12009
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>>
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owitworks_012009