Hi Paulo,
You can read ESRI ASCII grids (amongst many others) using rgdal package:
library(rgdal)
d <- readGDAL("file1.asc")
See gdalDrivers() for a listing of the available file formats for your
package build.
The read above would result in a single-colum SpatialGridDataFrame -
named "band1". To add further files as a new column (assuming the
subsequent files have exactly the same grid topology):
d$band2 <- readGDAL("file2.asc")$band1
. . . and so on.
To obtain the resulting raster bands as individual matrices you can use
as.image.SpatialGridDataFrame:
m1 <- as.image.SpatialGridDataFrame(d[1])$z
m2 <- as.image.SpatialGriddataFrame(d[2])$z
. . .
Then use your matrices as needed. If you only want the matrices and not
the intermediate SGDF objects, use readGDAL directly:
m1 <- as.image.SpatialGridDataFrame(readGDAL("file1.asc")[1])
. . .
These could be collected in a single 3-way array, or a list of matrices
as needed.
HTH,
Mike.
Paulo Cardoso wrote:
Can R perform matrix algebra between ascii converted Esri grids? I'm
convinced that its trivial.
The question is a little more complex (from my point of view and
inexperience): I'm interested in perform cost surface and distance surface
analysis avoiding ArcGIS tools. Maybe R can deal with grid formatted as
matrices...
Maybe R could call FWtools to perform all calculations iteratively...
Paulo
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