[R-sig-Geo] R Raster to ArcGIS

[Ashton Shortridge]

Hi Matt (and list),

ArcGIS still (as far as I know) doesn't work with rectangular cells. This 
isn't a problem with the AsciitoGrid function, but I think is more 
fundamentally a problem with Arc's raster data structure.

The trick to getting around this may be to convert your matrix to a point 
object - with x, y, and z values - in R, where x and y correspond to the 
ground coordinates of each cell in the matrix. I think you would have to do 
this with your own code, but if you've programmed with arrays before it would 
not be difficult. Then interpolate these points to a square grid. The 
interpolation could be done in R (using gstat routines for example) or within 
a GIS (that is, write the xyz object to a text file, or perhaps straight to a 
shapefile, import it as a vector point set to a GIS, and then convert that to 
a raster.

Hope this helps,

Ashton


On Tuesday 29 July 2008, Matt.Farnsworth at aphis.usda.gov wrote:
> Dear list,
>
> I'm trying to bring an ASCII raster file into ArcGIS that resulted from
> calling the R function Tsp(), which is in the "fields" library, followed
> by the use of the function predict.surface() to generate the matrix of
> predicted values. These functions use many of the same inputs as the
> Krig() function in R. My problem is that the output is a symmetrical
> matrix of dimension NxN, however, because R outputs an NxN matrix it
> necessarily results in having a rectangular grid cell (e.g., x dimension
> is 50 and y dimension is 30) for any input data set whose spatial extent
> is not square.
>
> My question is; does anybody know how to import a rectangular grid from an
> ASCII raster file into ArcGIS using something other than the AsciiToGrid
> function in ArcGIS, which only allows for square grids?
>
> Thanks in advance for any help,
> Matt
>
> *************************************************
> Matt Farnsworth
> Disease Ecologist
> Spatial Epidemiology Unit
> Centers for Epidemiology and Animal Health

-- 
Ashton Shortridge
Associate Professor			ashton at msu.edu
Dept of Geography			http://www.msu.edu/~ashton
235 Geography Building		ph (517) 432-3561
Michigan State University		fx (517) 432-1671