[R-sig-Geo] Re: [R] A package for spatial data classes: request for comments

[Luc Anselin]

As I mentioned to Roger Bivand a few days ago, it might be a good
idea to take a look at the spatial classes in ESRI's ArcGIS. In my
view they are not 100% ready for statistical analysis, but the vector
classes are very well structured. What is missing is an efficient
way to incorporate "topology" (contiguity structure) to provide
an easy way to construct spatial weights. In GeoDa, we build this
from scratch, using the shape files, but  that's not the way it
should be (although very fast).
L.

On Monday, November 3, 2003, at 09:08 AM, Edzer J. Pebesma wrote:

> Barry Rowlingson wrote:
>
>>
>>> To be really useful, the class should include vector (polygon) data,
>>> and probably line elements. For this, I need help. The simples 
>>> approach
>>> would be to extend SpatialDataFrame to SpatialDataFramePolygon,
>>> and add for each row add the corresponding polygon.
>>
>>
>>  I think you need to stop thinking about building classes at the 
>> moment, and to think about specifying _interfaces_. What methods do 
>> we want for spatial data? How will functions get the spatial data out 
>> of the objects? Then we can build classes that implement these 
>> interfaces.
>
> Baz, I agree that interfaces are important. Still, concentrating on 
> interfaces _only_
> does encourage package writers to come up each with a new set of 
> spatial classes
> -- something I would like to discourage: sharing more code makes the 
> code more
> reliable.
>
> I did build upon your idea of sp.coords, but called it coordinates, 
> and used reference (column name/numbers) instead of actual values:
>
> coordinates(meuse) = c("x", "y")
>
> I prefer coordinates because at some stage the S3 method mechanism may
> interpret sp.coords as an sp method for a coords class.
>
> My question, in your perspective, would be: which methods do we need 
> for
> a generic class containing vector/polygon data?
>
> E.g. how is,
>
> polygons(world) # gets or sets the polygons, as a list of 2 col 
> matrices
> polygonAttributes(world) # gets or sets the polygon attributes, as 
> data frame
> --
> Edzer
>
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----------------------------------------------------------------
Luc Anselin, PhD.
Faculty Excellence Professor and Director
Spatial Analysis Laboratory
Dept. Agricultural and Consumer Economics
University of Illinois at Urbana-Champaign
http://sal.agecon.uiuc.edu/