[R-sig-Geo] R/ArcGis and R-DCOM?

[Roger Bivand]

On Thu, 29 Nov 2007, paallen at attglobal.net wrote:

> Hi all,
>
> I am an ArcGis and R user.  I normally just share data between the two 
> with the old import/export game using csv, pdf, and jpg file.  Lately I 
> have just started to looked into the R-DCOM project and the r/arcgis 
> repository 
> (http://perso.univ-lr.fr/csainte/recherche/rarcgis/index.html).

This site was current for ArcGIS 8, but it seems that for ArcGIS 9, the 
Python interface using win32com.client to access the geoprocessor is 
easier to get running. One can call a short Python script from the R 
system() command, or call R from a Python script run from ArcGIS 
(typically using the R (D)COM StatConnector, or have a Python script use 
both.

Two useful links are:

http://code.env.duke.edu/projects/mget

and

http://courses.washington.edu/geog465/

where only MGET uses R, but the UW course provides a lot of useful 
guidance. Unfortunately, a University of Bergen course that we've just 
finished is only on an intranet - the general conclusions were that 
"things take time", and that the simplest scripts are the ones that work; 
beyond that, much of the documentation needs patience because many things 
do not work either at all, or as described - however, there are usually 
workarounds. Stopping using the ModelBuilder was crucial in most cases - 
it was far too difficult to debug - running code step-by-step from the 
Python command prompt was the main mode of learning. Styrk Finne (a 
participant) found that deleting the geoprocessor seemed to help on lab 
machines that were seldom shut down - the GP seems to be started at boot 
and accumulates zombie connections until it becomes unstable (in 9.1 and 
for our installation - laptop users who shutdown frequently could do more 
than users of the regular lab machines).

Most often the exchange is still by a subset of filetypes, but a good deal 
is possible. This, combined with the use of drivers for raster and vector 
data in the rgdal package, means that a lot can be streamlined.

> I am hoping to use it to streamline the sharing of data between the two 
> easier.  Specifically I am wanting to use r for some gridding and have 
> it save the rasters into native arcgis rasters and automatically paste 
> histograms/ecdf graphs onto layouts and plot princomp scores.
>

This imports an ASCII raster as written with writeAsciiGrid() in the 
maptools package - there are ways to use the AAIGrid driver in rgdal too - 
into Arc 9.1:

# import modules
import sys, os
from win32com.client import Dispatch

script = sys.argv[0]

# initialize ESRI ArcGIS geoprocessor
print "Initialising ArcGIS geoprocessor ..."
GP = Dispatch('esriGeoprocessing.GpDispatch.1')
GP.CheckOutExtension('Spatial')
GP.OverwriteOutput = 1    # setup for overwrite

out_ascii_grid = sys.argv[1]

out_ascii_type = sys.argv[2]

gridPath = sys.argv[3]

in_grid = sys.argv[4]

inRaster = gridPath + "/" + in_grid
try:
    GP.ASCIIToRaster_conversion(out_ascii_grid, inRaster, out_ascii_type)
except:
    msg = 'GP Error: %s' % GP.GetMessages()
    GP.AddError(msg); print msg; raise

del(GP)

(very rough, but apart from error handling, you can see how you might pass 
the arguments from system() in R).

To get R (D)COM Python support running, see the samples/scripts directory 
of the R(D)COM install - essentially a one-off build in Pythonwin of the 
COM hooks for the StatConnector server.

In rgdal, look at gdalDrivers() and ogrDrivers() to see what is available 
- the standard Windows binary package has plenty of drivers for reading 
things (but convert personal geodatabase files to say shapefiles or 
coverages using the GP to read), and many fewer for writing to Arc - 
again, use the GP to convert back.

Hope this helps,

Roger

PS. It would be very helpful if others with relevant experience could join 
this thread, which can then be linked from the Rgeo website.

> I have tried the raster example on the r/arcgis repository page without luck.
>
> Has anyone else tried this or something similar?
>
> Regards,
>
> Phillip Allen
> Geochemist
>
> Sent via BlackBerry by AT&T
>
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no