[R-sig-Geo] GIS Tasks in R

[Roger Bivand]

On Tue, 6 Feb 2007, CJ Jackson wrote:

> Hi everyone,
> 
> I'm currently working on my PhD (geology) and would like to explore the 
> possible GIS capabilities of R.  I currently use ESRI's ArcView (3.x), 
> ArcGIS (9.1), and ArcInfo (9) software for all of my GIS work.  I have 
> written an "extension" for the old ArcView that performs various 
> analyses of points/polylines/polygons and have been wanting to update 
> the extension for the latest version of ArcGIS to help me solve various 
> research problems.  With that being said, I discovered 'R' last year and 
> fell in love with it and have been using it for data analysis of 
> attribute tables from GIS Shapefiles.  Ultimately, as part of my 
> research, I would like to make a package for R that would handle various 
> GIS tasks of shapefiles themselves, not just their data tables.  It 
> would be great to have a analysis package for my research that is not 
> solely dependent on ESRI's software.  Furthermore, I dread programming 
> in Visual Basic for the new ArcGIS because I have limited programming 
> skills.  

There are a number of possibilities for computing on the geometries, using 
the classes defined in the sp package as containers. There is no direct 
interface to the Geom functionality in GDAL/OGR, so access to 
computational geometry is patchy, and spread across several packages.

> Here are some of the tasks I would like to perform:
> 
> - produce a new point shapefile that contains points where two or more 
> shapefiles with polylines intersect

This involves finding the crossing point of the polylines, and may be
somewhere, probably an internal function in the spatstat package - see
?distppll for a list (the functions are described as not being for users
to call directly, but I've found those I've used very solid). There may be 
suitable code in the PBSmapping package.

> - intersect two or more shapefiles with polygons and store the results 
> in a new shapefile

Either the PBSmapping package or use gpclib with sp and maptools (there is 
a function for merging SpatialPolygons in a single set of shapes in 
maptools using gpclib).

> - calculate area of polygons

Code lots of places, sp, PBSmapping, spatstat, splancs - the main issues 
are what to do with holes.

> - calculate the distance from a point shapefile to another point shapefile
> 

spDistN1 in sp, stepping over the coordinates in one set for all in the 
other probably using *apply(), or alternatives in spatstat or splancs.

I'm assuming that the geometries are all projected, if not, things get a 
bit more interesting.

> Is this possible in R, or, am I barking up the wrong tree?  Thanks!
> 

library(fortunes)
fortune("Yoda")

Roger

> cj
> 
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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