[R-sig-Geo] question about rgeos "gDistance" parameters

[Roger Bivand]

Please post plain text only - since you didn't provide an example, your 
code wasn't deformed by HTML formatting, but had you provided an example 
it would have been. Did you look at the examples on the help page?

library(rgeos)
pt1 = readWKT("POINT(0.5 0.5)")
pt2 = readWKT("POINT(2 2)")

p1 = readWKT("POLYGON((0 0,1 0,1 1,0 1,0 0))")
p2 = readWKT("POLYGON((2 0,3 1,4 0,2 0))")

gDistance(pt1,pt2)
gDistance(p1,pt1)
gDistance(p1,pt2)
gDistance(p1,p2)

Modifying this:

pt3 <- rbind(pt1, pt2)
row.names(p2) <- "2"
p3 <- rbind(p1, p2)
gDistance(pt3, p3)
gDistance(pt3, p3, byid=c(TRUE, TRUE))
gDistance(pt3, p3, byid=c(TRUE, FALSE))
gDistance(pt3, p3, byid=c(FALSE, TRUE))

Hope this clarifies,

Roger

On Fri, 10 Nov 2017, Julie Lee-Yaw via R-sig-Geo wrote:

> Can someone better explain what the byid parameter does in the gDistance 
> command? The help for the command states: "Logical vector determining if 
> the function should be applied across ids (TRUE) or the entire object 
> (FALSE) for spgeom1 and spgeom2"
>
> If spgeom1 is a spatial points objects and spgeom2 is a shapefile with 
> multiple polygons, will byid=FALSE return a single value and byid=TRUE 
> return a matrix of the distances between every point and every polygon? 
> If I'm correct, what does that single value represent (e.g. which 
> distance) when byid=TRUE? Thanks
> 	[[alternative HTML version deleted]]
>
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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; e-mail: Roger.Bivand at nhh.no
Editor-in-Chief of The R Journal, https://journal.r-project.org/index.html
http://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en