[R-sig-Geo] Splitting spatial lines at self intersections (line crossings)

[Marcelino de la Cruz Rot]

You should load before library(maptools) and the coercion is done.

Cheers

Marcelino




El 26/01/2018 a las 13:12, Michael Sumner escribió:
> Ege: I don't believe that this code is enough to get coercion between sp
> and spatstat:
>
> pts <- cbind(c(120:123,121,125),c(100,100,104,102,99,98))
> pt2 <- cbind(c(124,124,123,118,124,125),c(100,97,100,104,106,110))
> library(sp)
> library(spatstat)
> L1 <- SpatialLines(list(Lines(list(Line(pts)), "X")))
> L2 <- SpatialLines(list(Lines(list(Line(pt2)), "X")))
> l1 <- as.psp(L1)
> l2 <- as.psp(L2)
> int <- crossing.psp(l1, l2)
>
> Are we relying on some other code, or perhaps a specific version of
> spatstat or its family?  (I know ways to convert from Spatial to psp, but I
> was taken by this apparent lack of infrastructure - and I'm very keen on
> seeing more bridges between these rich worlds).
>
> Cheers, Mike
>
>
> On Fri, 26 Jan 2018 at 17:48 Ege Rubak <rubak at math.aau.dk> wrote:
>
>> The `psp` class in spatstat consists of individual line segments and
>> `selfcrossing.psp` checks whether each individual line intersects one of
>> the other lines, which happens at all the points in your plot.
>>
>> If instead you treat each of the two line sequences as a `psp` you can
>> check find the crossings of the two `psp` objects. I.e., continuing your
>> code (with `spatstat` and `maptools` loaded):
>>
>> L1 <- SpatialLines(list(Lines(list(Line(pts)), "X")))
>> L2 <- SpatialLines(list(Lines(list(Line(pt2)), "X")))
>> l1 <- as.psp(L1)
>> l2 <- as.psp(L2)
>> int <- crossing.psp(l1, l2)
>>
>> This gives you the four intersections between the lines. I don't know of
>> a simple way to do the next task in `spatstat`. A useful function if you
>> are going to try to write some code is `test.crossing.psp` which gives
>> you a logical matrix indicating which segments cross.
>>
>> Cheers,
>> Ege
>>
>> On 01/25/2018 11:26 PM, Glenn Stauffer wrote:
>>> I have a Spatial Lines object I would like to split at every point where
>> the
>>> line self-intersects (crosses or touches itself), or anywhere lines touch
>>> each other, if there are multiple lines.
>>>
>>> I've tried using spatstat to convert the SpatialLines to a psp object and
>>> then use the selfcrossing.psp function to find the intersection points
>> (see
>>> example below). But that seems to identify all the nodes, not just the
>>> points where the line crosses. Also, even if it identified only the
>>> crossings (which is what I want), I am not sure how to perform the next
>> step
>>> and split the lines at those points.
>>>
>>> So, 1) I need to identify the crossings/touches, and 2) split the lines
>> at
>>> those points.
>>>
>>>
>>>
>>> Essentially, what I am looking for is an R equivalent to the planarize
>>> function in ArgGIS. Is there a relatively easy way to do this in R?
>>>
>>>
>>>
>>> Thanks,
>>>
>>> Glenn
>>>
>>>
>>>
>>> Here is an example of what I have tried.
>>>
>>>
>>>
>>>
>>>
>>> pts <- cbind(c(120:123,121,125),c(100,100,104,102,99,98))
>>>
>>> pt2 <- cbind(c(124,124,123,118,124,125),c(100,97,100,104,106,110))
>>>
>>> projstr <- "+init=epsg:3071"         # make everything in meters
>>>
>>> L <- SpatialLines(list(Lines(list(Line(pts),Line(pt2)),"X")),proj4string
>> =
>>> CRS(projstr))
>>>
>>> plot(L)
>>>
>>> PSP <- as.psp.SpatialLines(L)
>>>
>>> int <- selfcrossing.psp(PSP)
>>>
>>> plot(int,add=TRUE,col="red") # identifies more than just the crossings
>>>
>>>
>>>
>>>
>>>        [[alternative HTML version deleted]]
>>>
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-- 
Marcelino de la Cruz Rot
Depto. de Biología y Geología
Física y Química Inorgánica
Universidad Rey Juan Carlos
Móstoles España