The getRasterData command in rgdal will return a subset of the image given an rgdal object handle. I believe you can now also use simple array [] operations as well.
THK On 6/1/07, Andrew Niccolai <[EMAIL PROTECTED]> wrote: > Greetings Spatial R users/developers, > > I was curious as to whether or not it would be possible to describe a > bounding box for a large image so that what is read into R would be just the > contents of the image inside the bounding box. Conceptually, it would be > akin to "clipping" the image but without the image read into the program. > My issue is that I have a very large 3-band orthophoto of several hundreds > of hectares of forest (roughly 8MB image). I am running an analysis of > LIDAR data that requires the user to select a smaller area of a highly > degraded lidar image. I would like the bounding box of this LIDAR area to > be used to "clip" a georegistered orthophoto that complements the LIDAR > data. However, the complete ortho image seems to crash my WindowsXP, R > v2.4.1 setup. When I take the bounding box coordinates into ERDAS Imagine > and subset the orthophoto the following code works fine to bring it into R: > > ## Read in Tif file > setwd(anypathway) > tif.image <- "Pre_Subset_Image.tif" > LIDAR.tif <- GDAL.open(tif.image) > dim(LIDAR.tif) > image(LIDAR.tif[,,1]) > > ## This converts the rgdal class to an SpatialGridDataFrame class > LIDAR.tif.1 <- LIDAR.tif[,] > bbox(LIDAR.tif.1) > image(LIDAR.tif.1,main="") > mtext("Orthophoto of Preloaded Fusion Example", side=3, line = 3, font=3, > cex=1.25) > > > However, this would be impractical with the code that I am building to jump > out of R and subset images in Imagine (plus very expensive for the end > user). Therefore, does anyone have any solutions for reading in an image > that would work in theory like the following: > > setwd(anypathway) > tif.image <- "VERY_LARGE_IMAGE.tif" > Bounded.tif <- GDAL.open(tif.image, bbox=c(UpL.X, LwR.X, UpL.Y, LwR.Y)) > > By the way, I am not set on GDAL.open as the solution but it seems to work > well reading in Tifs & Jpegs. > > Again, thanks in advance > > > Andrew Niccolai > Doctoral Candidate > Yale School of Forestry > > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@stat.math.ethz.ch > https://stat.ethz.ch/mailman/listinfo/r-sig-geo > -- Timothy H. Keitt, University of Texas at Austin Contact info and schedule at http://www.keittlab.org/tkeitt/ Reprints at http://www.keittlab.org/tkeitt/papers/ ODF attachment? See http://www.openoffice.org/ _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo