[R-sig-Geo] Which dimension should a matrix returned by a binary topological operaor have?

[Edzer Pebesma]

In sp and rgeos, we currently have

> library(sp)
> library(rgeos)
> p1 = SpatialPoints(matrix(1:4,2))
> p2 = SpatialPoints(matrix(1:6,3))
> gRelate(p1,p2,byid=TRUE)
  1           2
1 "FF0FFF0F2" "FF0FFF0F2"
2 "FF0FFF0F2" "FF0FFF0F2"
3 "FF0FFF0F2" "FF0FFF0F2"
> dim(gRelate(p1,p2,byid=TRUE))
[1] 3 2
> length(p1)
[1] 2
> length(p2)
[1] 3

Meaning: arguments with lengths 2 and 3 result in a 3 x 2 matrix. This
is true for all binary operators (covers, intersects, etc) and byid=TRUE.

I always found this counterintuitive, and consider implementing it the
other way around (2 and 3 -> 2 x 3) in package sf. Or am I overlooking
something obvious?
-- 
Edzer Pebesma
Institute for Geoinformatics  (ifgi),  University of Münster
Heisenbergstraße 2, 48149 Münster, Germany; +49 251 83 33081
Journal of Statistical Software:   http://www.jstatsoft.org/
Computers & Geosciences:   http://elsevier.com/locate/cageo/

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