how to plot specific segment from density.lpp

Question

I use density.lpp for kernel density estimation. I want to pick specific segment in that and plot the estimation through chosen segment. As an example, I have a road which is a combination of two segments. each segments have different length so I don't know how many pieces each of them are divided by.

here is the locations of vertices and road segment ids. https://www.dropbox.com/s/fmuul0b6lus279c/R.csv?dl=0

here is the code I used to create spatial lines data frame and random points on the network and get density estimation.

Is there a way to know how many pieces each segment divided by? OR if I want to plot locations vs estimation for chosen segment how can I do? Using dimyx=100 created 199 estimation points but I don't know how many of them belongs to Swid=1 or Swid=2.

One approached I used was, using gDistance it works fine in this problem because these segments connected to one directions however, when there is 4 ways connection, some of the lambda values connects to another segments which is not belongs to that segment. I provided picture and circled 2 points, when I used gDistance, those points connected to other segments. Any ideas?

R=read.csv("R.csv",header=T,sep=",")
R2.1=dplyr::select(R, X01,Y01,Swid)

coordinates(R2.1) = c("X01", "Y01")
proj4string(R2.1)=CRS("+proj=utm +zone=17 +datum=NAD83 +units=m +no_defs +ellps=GRS80 +towgs84=0,0,0")
plot(R2.1,main="nodes on the road")


## 
LineXX <- lapply(split(R2.1, R2.1$Swid), function(x) Lines(list(Line(coordinates(x))), x$Swid[1L]))

## 
linesXY <- SpatialLines(LineXX)
data <- data.frame(Swid = unique(R2.1$Swid))
rownames(data) <- data$Swid
lxy <- SpatialLinesDataFrame(linesXY, data)
proj4string(lxy)=proj4string(trtrtt.original)

W.1=as.linnet.SpatialLines(lxy)

Rand1=runiflpp(250, W.1) 
Rand1XY=coords(Rand1)[,1:2]

W2=owin(xrange=c(142751.98, 214311.26), yrange=c(3353111, 3399329))

Trpp=ppp(x=Rand1XY$x, y=Rand1XY$y, window=W2)    ### planar point object
L.orig=lpp(Trpp,W.1) # discrete 
plot(L.orig,main="Original with accidents")


S1=bw.scott(L.orig)[1]  # in case to change bandwitdh
Try274=density(L.orig,S1,distance="path",continuous=TRUE,dimyx=100)  
L=as.linnet(L.orig)
length(Try274[!is.na(Try274$v)])
[1] 199

Answer 1

This is a question about the spatstat package.

The result of density.lpp is an object of class linim. For any such object, you can use as.data.frame to extract the data. This yields a data frame with one row for each sample point on the network. For each sample point, the data are xc, yc (coordinates of nearest pixel centre), x,y (exact coordinates of sample point on network), seg (identifier of segment), tp (relative position along segment) and values (the density value). If you split the data frame by the seg column, you will get the data for invididual segments of the network.

However, it seems that you may want information about the internal workings of density.lpp. In order to achieve adequate accuracy during the computation phase, density.lpp subdivides each network segment into many short segments (using a complex set of rules). This information is lost when the final results are discretised into a linim object and returned. The attribute "dx" reports the length of the short segments that were used in the computation phase, but that's all.

If you email me directly I can show you how to extract the internal information.