[R-sig-Geo] How to segment or split a spatial line in R

[Robert J. Hijmans]

I should add that you can use geosphere::midPoint if you wanted the
great circle (longitude/latitude) mid-point instead of the Cartesian
midpoint.
But I now also see that you did not ask for splitting into
pre-existing segments, but into new ones ---- Edzer's solution seems
appropriate for that...
Robert

On Thu, Oct 23, 2014 at 9:46 AM, Robert J. Hijmans <r.hijmans at gmail.com> wrote:
> I think the below is a solution:
>
> library(raster)
> # create some lines
> cds1 <- rbind(c(-180,-20), c(-140,55), c(10, 0), c(-140,-60))
> cds2 <- rbind(c(-10,0), c(140,60), c(160,0), c(140,-55))
> cds3 <- rbind(c(-125,0), c(0,60), c(40,5), c(15,-45))
> lns <- SpatialLines(list(Lines(list(Line(cds1)), "1"),
>      Lines(list(Line(cds2)), "2"), Lines(list(Line(cds3)), "3") ))
>
>
> # get coordinates
> xy <- as.data.frame(lns, xy=TRUE)
>
> # get midpoints
> x <- xy$x[-1] + (xy$x[-nrow(xy)] - xy$x[-1]) / 2
> y <- xy$y[-1] + (xy$y[-nrow(xy)] - xy$y[-1]) / 2
> m <- cbind(x,y)
>
> # remove mid-points between non-segments
> i <- xy$cump[-1] == xy$cump[-nrow(xy)]
> m <- m[i,]
>
> plot(lns)
> points(m)
>
>
> On Thu, Oct 23, 2014 at 8:56 AM, Edzer Pebesma
> <edzer.pebesma at uni-muenster.de> wrote:
>> sp::spsample also offers regular sampling of points on SpatialLines objects.
>>
>> On 10/23/2014 05:21 PM, Mathieu Basille wrote:
>>> May be a little bit far fetched, but maybe check 'redisltraj' from the
>>> adehabitatLT package (and section 4.2.2 of the vignette [1]). Note that
>>> it was intended for animal trajectories so might be a little bit out of
>>> scope for you.
>>>
>>> Mathieu.
>>>
>>>
>>> [1]
>>> http://cran.r-project.org/web/packages/adehabitatLT/vignettes/adehabitatLT.pdf
>>>
>>>
>>> Le 23/10/2014 10:10, Manuel Spínola a écrit :
>>>> Dear list members,
>>>>
>>>> How to segment or split a spatial line in shorter equal segments, and
>>>> also,
>>>> how to get the mid point of ecah segment.
>>>>
>>>> Best,
>>>>
>>>> Manuel
>>>>
>>>
>>
>> --
>> Edzer Pebesma,  Co-Editor-in-Chief Computers & Geosciences
>> Institute for Geoinformatics (ifgi), University of Münster
>> Heisenbergstraße 2, 48149 Münster, Germany. Phone: +49 251
>> 83 33081 http://ifgi.uni-muenster.de GPG key ID 0xAC227795
>>
>>
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