R Raster to ArcGIS

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

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

Hi list,

I'm going to borrow what I just learned from my other thread.  I'd
export your raster data as an ENVI file, which ArcGIS should be able
to read with the ENVI Reader for ArcGIS installed.

1. Go to www.ittvis.com and download the appropriate version of the
ENVI Reader for ArcGIS (1.1 for ArcGIS 8.3-9.1, 1.2 for ArcGIS 9.2).
You won't need the ENVI reader for ArcGIS 9.3 as support for this
format is in the upcoming version.
2. Get the caTools package for R and load it.
3. Export your data from R using write.ENVI
4. Read data into ArcGIS using usual means.

You could also see if one of the other packages, e.g., RPyGeo, allows
you to directly interface between R and ArcGIS for your purposes.

Best of luck,
Guy Serbin

On Tue, Jul 29, 2008 at 2:54 PM, Ashton Shortridge <ashton at msu.edu> wrote:

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