[R-sig-Geo] Union sp polygons ID (rgoes and sp)

[Roger Bivand]

On Sat, 16 Mar 2013, Omphalodes Verna wrote:

> Thanks Roger!
>
> No, there is no mistaking. This is kind of dissolve function. But I need 
> overlapping / intersection of polygons, where common polygons have 
> unique ID

Well, certainly your example is unclear. You are taking the unions 
byid=TRUE of 5 Polygons objects with the same objects, so if you start 
with

set.seed(1)

you get:

> gArea(SPLpoly, byid=TRUE)
          1          2          3          4          5
0.04823433 0.03769229 0.04274933 0.06575346 0.09910228

and

> gArea(gU, byid=TRUE)
        1 1        1 2        1 3        1 4        1 5        2 1
0.04823433 0.06825532 0.09098365 0.11398779 0.14733661 0.06825532
        2 2        2 3        2 4        2 5        3 1        3 2
0.03769229 0.08044161 0.10344575 0.13679457 0.09098365 0.08044161
        3 3        3 4        3 5        4 1        4 2        4 3
0.04274933 0.10850279 0.14076253 0.11398779 0.10344575 0.10850279
        4 4        4 5        5 1        5 2        5 3        5 4
0.06575346 0.14303501 0.14733661 0.13679457 0.14076253 0.14303501
        5 5
0.09910228

where 1 1, 2 2, etc. agree with the single Polygons values. If byid=TRUE, 
you get the union of the two Polygons objects, see:

plot(gU[2])

and

gEquals(gU[2], gU[6])

It isn't clear what you want.

Roger

>
> Thanks
>
>
>
>
> ----- Original Message -----
> From: Roger Bivand <Roger.Bivand at nhh.no>
> To: Omphalodes Verna <omphalodes.verna at yahoo.com>
> Cc: "r-sig-geo at r-project.org" <r-sig-geo at r-project.org>
> Sent: Saturday, March 16, 2013 4:34 PM
> Subject: Re: [R-sig-Geo] Union sp polygons ID (rgoes and sp)
>
> On Sat, 16 Mar 2013, Omphalodes Verna wrote:
>
>> Dear list.
>> 
>> I would like to do union of many polygons in R (rgeos) with ''gUnion'' function (in attached code only 5). Final result should be polygons with unique ID (using attached code it is), but when I plot them (colors by ID value), there are only 5 polygons. Please, give me some idea. Thanks to all, OV
>
> Are you mistaking gUnion() for gUnaryUnion()?
>
> gU = gUnaryUnion(SPLpoly, id=rep("1", length(SPLpoly)))
>
> Roger
>
>> 
>> RCode:
>> library(rgeos)
>> library(sp)
>> n <- 5
>> xy <- cbind(runif(n), runif(n), runif(n), runif(n))
>> LLine <- vector("list", n)
>> LLines <- vector("list", n)
>> for(i in 1:n) LLine[[i]] <- Line(rbind(xy[i, 1:2], xy[i, 3:4]))
>> for(i in 1:n) LLines[[i]] <- Lines(LLine[[i]], ID = i)
>> SPLines <- SpatialLines(LLines)
>> SPLpoly <- gBuffer(SPLines, width = 0.05, byid = TRUE)
>> plot(SPLines, col = getSLLinesIDSlots(SPLines))
>> plot(SPLpoly, add = TRUE, col = getSLLinesIDSlots(SPLines))
>> SPLpolyA <- SPLpoly
>> SPLpolyB <- SPLpoly
>> gU = gUnion(SPLpolyA, SPLpolyB,  byid = TRUE)
>> plot(gU, col = rainbow(length(gU)))
>> 
>> 
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>> 
>
> -- Roger Bivand
> Department of Economics, NHH Norwegian School of Economics,
> 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
>

-- 
Roger Bivand
Department of Economics, NHH Norwegian School of Economics,
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