Using RGDAL to "copy" header information... (Jonathan Greenberg)

Thu, Nov 6, 2008 5:56 AM

Sorry, I hit the send button unintentionally

Next try:

The output file is a binary file with a text (ini type) header. It is
fairly trivial to write other, more standard, hdr files, and I will
add that over the coming weeks.
If you do not want to build the package, just have a look at the
raster.write.R file in the code repository. You will able to see how
we do it.

Robert

Message: 2
Date: Wed, 05 Nov 2008 09:18:47 -0800
From: Jonathan Greenberg <greenberg at ucdavis.edu>
Subject: [R-sig-Geo] Using RGDAL to "copy" header information...
To: gdal-dev at lists.osgeo.org, R-sig-Geo at stat.math.ethz.ch,
       r-help at r-project.org
Cc: Solomon Dobrowski <solomon.dobrowski at cfc.umt.edu>
Message-ID: <4911D577.2050300 at ucdavis.edu>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

R-geographers...

I'm trying to solve a problem to implement a line-by-line tiled
processing using RGDAL (read 1 line of an image, process the one line,
write one line of the image to a binary file).  Everything except for
the final step I'm able to do using a combination of RGDAL and r-base
commands.  Below is the basic structure, the input file "elev" can be
any image file GDAL supports -- the code below just "copies" the image
one line at a time:

###

library(rgdal)
infile='elev'
outfile_base='testout'
outfile_ext='.bil'
outfile=paste(outfile_base,outfile_ext,sep='')
outcon <- file(outfile, "wb")

infile_info=GDALinfo(infile)
nl=infile_info[[1]]
ns=infile_info[[2]]

for (row in 1:nl) {
   templine <- readGDAL(infile,region.dim=c(1,ns),offset=c(row-1,0))
   writeBin(templine[[1]], outcon,size=4)
}
close(outcon)
# Below doesn't work
# writeGDAL(templine,outfile_base,drivername='EHdr',type="Float32")

###

The issue is this: I need to be able to effectively copy the
geographic/header information from the input file (the last line almost
works, but as you can see it sets the line #s to 1, not "ns"), and parse
it over to the output file (which is some form of a flat binary file --
in this case, an Arc Binary Raster, but an ENVI binary output would also
be good) -- ideally I'd like to be able to modify this header,
particularly the number type (e.g. if the input file is an integer, and
I'm writing out a floating point binary, I need that reflected in the
output header).  I can do this by *manually* creating the output header
via a series of ascii-writes, but I was wondering if there is a more
effective way of doing this using RGDAL that might apply generically to
the header of any binary image file I might write?  Thanks!

--j

--

Jonathan A. Greenberg, PhD
Postdoctoral Scholar
Center for Spatial Technologies and Remote Sensing (CSTARS)
University of California, Davis
One Shields Avenue
The Barn, Room 250N
Davis, CA 95616
Cell: 415-794-5043
AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307

Using RGDAL to "copy" header information... (Jonathan Greenberg)

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