[R-sig-Geo] How to create a SpatialMultiPoints object

[Roger Bivand]

On Mon, 14 Apr 2014, Stefan Jelkovich wrote:

> Roger,
>
> you are right. In case of the meuse data it makes no sense at all. Not 
> the best example... I do not see a clear adventage for the use of 
> MultiPoints, too. Maybe in case of categorical data? I only wanted to 
> create such an object to investigate the structure and prepare my 
> functions for MultiPoint objects.
>
> So MultiPoints are not supported by the SpatialPoints and 
> SpatialPointsDataFrame classes? That's fine for me.
>
> By the way: if MultiPoint objects are imported in R and converted to 
> SpatialPoints, the MultiPoint structure is just gone?

library(rgeos)
g4=readWKT("MULTIPOINT((3.5 5.6),(4.8 10.5))")
g4
class(g4)
str(g4)
slot(g4, "coords")

(they get identical rownames in the coordinate matrix, but by default 
there is no key/ID checking for points, so this is not reliable). The fact 
that the points belong to a multipoint geometry is not recorded anywhere 
as it is an attribute of the points.

In your use case, the categorical observations have point support, not 
multipoint support, so grouping points with the same category level is a 
choice the user makes, but does confuse support. It could be done, but 
would involve a lot of shoehorning to associate the points with their 
appropriate geometry, and makes no great sense.

Roger


>
> Thanks
> Stefan
>
>>> Am 13.04.2014 um 20:57 schrieb Roger Bivand <Roger.Bivand at nhh.no>:
>>> 
>>> On Sun, 13 Apr 2014, Stefan Jelkovich wrote:
>>> 
>>> Hi all,
>>> 
>>> I’m struggling with the creation of a SpatialPoints/SpatialPointsDataFrame object containing MultiPoints. Is this possible at all?
>> 
>> Why would it be possible, as each geomtry feature (point) is associated with unique observed data values? A multipoint object is of little use in point pattern analysis or geostatistics (or other areas of spatial statistics) as its support is hard to use - the single unique observed data value for each geometry would be associated with multiple points, and a set of such objects might well overlap mutually, meaning that it would be very hard to retrieve observations.
>> 
>> If you feel that multipoint objects have a future in spatial statistics, please contribute a suitable class container and methods for handling it.
>> 
>> Hope this clarifies,
>> 
>> Roger
>> 
>>> 
>>> # SinglePoints are that easy:
>>> library(sp)
>>> data(meuse)
>>> coordinates(meuse) <- ~x+y
>>> 
>>> # MultiPolygons are that easy:
>>> p1 <- Polygon(cbind(x=c(0, 0, 10, 10, 0), y=c(0, 10, 10, 0, 0)))
>>> p2 <- Polygon(cbind(x=c(13, 13, 17, 17, 13), y=c(13, 17, 17, 13, 13)))
>>> lp <- list(p1, p2)
>>> pls <- Polygons(lp, ID="1")
>>> mp <- SpatialPolygons(list(pls))
>>> 
>>> How can I put all the meuse data points in one MultiPoint object?
>>> 
>>> Stefan
>>> 
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>> 
>> -- 
>> Roger Bivand
>> Department of Economics, Norwegian School of Economics,
>> Helleveien 30, N-5045 Bergen, Norway.
>> voice: +47 55 95 93 55; fax +47 55 95 91 00
>> e-mail: Roger.Bivand at nhh.no
>
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-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: Roger.Bivand at nhh.no