[R-sig-Geo] R 3.0.0 and spatial classes

[Edzer Pebesma]

On 12/16/2012 08:58 PM, Barry Rowlingson wrote:
> On Sun, Dec 16, 2012 at 6:53 PM, Chris English <sglish at hotmail.com> wrote:
>>
>> Edzer:
>> On Tue, Jul 17, 2012 at 2:34 PM, Agustin Lobo ~ from Barry Rowlingson
>> wrote:
>> To convert to SpatialLines, get the coordinates and build in the
>> usual convoluted manner:
>>
>>  > s=data.frame(x=runif(10),y=1:10,z=rnorm(10))
>>  > coordinates(s)=~x+y
>>  > L = SpatialLines(list(Lines(list(Line(coordinates(s))),"X")))
>>  > plot(L)
>> Convoluted is not the same as orphaned, certainly, but one gets the sense that
>> 'Line' owes its existence to matters of plotting rather than line as line, independent of
>> drawing it, and this may have some import upon line analysis and the possibility of
>> arriving at topology and dispensing with shared lines and the like.
> 
>  "Line" is a non-spatial Line, made up from an ordered set of (x,y)
> coordinate pairs. It cannot have a coordinate system assigned to it.
> 
>  "Lines" is a list of Lines, making a non-spatial set of Line
> segments. It too cannot have a coordinate system assigned.
> 
>  "SpatialLines" is a spatial set of Lines, for when you have a number
> of features each of which may be composed of several disconnected
> segments. It can have a coordinate system assigned.
> 
>  You are making a SpatialLines object where a single feature has a
> single line segment. The slightly annoying
> list(Lines(list(Line(...)))) dance is unavoidable because the lists
> are necessary since the lists can have more than one element, but you
> could easy create a 'SimpleSpatialLine' function that did all that. It
> might even make sp for R 3.0.0! (SimpleSpatialPolygon might be handy
> too...)

Nice idea -- or a "simple" method that does it with whatever you feed it
with? Or simply "c" methods, like c(Line1,Line2,Line3) creating a
SpatialLines object?

@Chris: the convolution of lines is identical to that of polygons, as is
its lack of topology and facilities for analysis.

> 
> Another possibility might be to write methods for SpatialLines that
> takes a matrix and skips the complexity for simple cases...

like, a n x 2 matrix with NA-separated lines?

> 
> Barry
> 

-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de