I'm currently doing a lot of simple GIS work in R, including points
in polygon queries. My .Rprofile file has
require(maptools)
require(rgdal)
With that as a starting point, I find that the data structures play
well together.
Define a coordinate reference system object with
crs.ll <- CRS('+proj=longlat +ellps=GRS80 +datum=NAD83 +no_defs')
Load a shapefile with
my.shp <- readOGR('directoryname','filename', p4s=CRSargs(crs.ll) )
This will give you an object of class SpatialPolygonsDataFrame.
readOGR() is in the rgdal package.
readShapeSpatial or readShapePoly from the maptools package should
work as well, and I used to use them, but lately I've been using
readOGR().
Then the overlay() function in the sp package will do your #2. But I
do think you'll need your points to be one of the SpatialPoints
classes.
Omitting the p4s argument from readOGR() might work, I'm not sure.
Or, I think you might be able to just supply the text string, i.e.,
p4s='+proj=longlat +ellps=GRS80 +datum=NAD83 +no_defs'
but I have found it handy to have several projections predefined, as in
crs.ll <- CRS('+proj=longlat +ellps=GRS80 +datum=NAD83 +no_defs')
crs.utm <- CRS('+init=epsg:32610')
for use in the spTransform() function.
Also, your question would go better on R-sig-geo mailing list.
A final note, some plotting functions need to have the sp package
earlier in the search() path than maptools.
-Don
At 9:37 AM -0600 4/1/10, Scott Duke-Sylvester wrote:
I have a simple problem: I need to load a ERSI shapefile of US states
and check whether or not a set of points are within the boundary of
these states. I have the shapefile, I have the coordinates but I'm
having a great deal of difficulty bringing the two together. The
problem is the various GIS packages for R do not play well with each
other. sp, shapefiles, maptools, etc all use different data
structures. Can someone suggest a simple set of commands that will
work together that will:
1) load the shapefile data.
2) Allow me to test whether or not a (lng,lat) coordinate pair are
inside or outside the polygons defined in the shapefile.
Many thanks,
scott.
--
Scott M. Duke-Sylvester
Assistant Professor
Department of Biology
Office : 300 E. St. Mary Blvd
Billeaud Hall, Room 141
Lafayette, LA 70504
Mailing address : UL Lafayette
Department of Biology
P.O.Box 42451
Lafayette, LA 70504-2451
Phone : 337 482 5304
Fax : 337 482 5834
email : smd3...@louisiana.edu
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--
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062
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