[R-sig-Geo] Outline of Study area

[Brian Oney]

Hi List,
I am mosaicking several maps of different areas and I would like to make 
an outline of the different study areas for plotting etc.. I have played 
around extensively in GRASS and R and still don't have what I need. I 
would like to do it in R because, at the moment, I am a windows slave, 
and windows slaves are especially disadvantaged in GRASS.

# In R I have tried:
rast[!is.na(rast)] <- 1
rasterToPolygons(rast, function(x) !is.na(x)) # This just overwhelmed my 
computer and gave me lots of little polygons


#Trying the same after using aggregate also did not help speed.
#So say that I am satisfied with the product from raster to polygons.
#Then I use:
unionSpatialPolygons(polyrange, IDs=somethingsane) # And it takes an 
additional several hours time as well as excludes my islands.

Does anyone have suggestion to create an outline in a reasonable amount 
of time?
I would greatly appreciate it!

Regards,
Brian