linepolygonqgissplitting
Is it possible in QGIS to split a line into segments given which polygon it falls within? I am using 2.8.
For example, a line that passes through three polygons will become three separate lines. Each time it crosses from one polygon into another it'd become a new line.
So in this case, where the green is a line, I would like to split it into three separate lines. Once for each time it crosses the black border of a polygon.
This can be done with the rgeos package, e.g. with gBuffer and gDifference:
library("rgeos")
library("rgdal")
line1 <- matrix(c(-1.81209, -1.80470, -1.80616, 55.68024, 55.67947,
55.67544), ncol=2)
line2 <- matrix(c(-1.80468, -1.80330, -1.79690, 55.68322, 55.68017,
55.67800), ncol=2)
line3 <- matrix(c(-1.79798, -1.80069, -1.78929, 55.68364, 55.68138,
55.67966), ncol=2)
lines <- SpatialLines(list(Lines(list(Line(line1)), ID="1"),
Lines(list(Line(line2)), ID="2"),
Lines(list(Line(line3)), ID="3")))
l <- SpatialLinesDataFrame(lines, data=data.frame(ID=paste(1:3)))
proj4string(l) <- CRS("+proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0")
lt <- spTransform(l, CRS("+init=epsg:27700 +datum=WGS84"))
plot(lt, lty=3)
buf_list <- vector(3, mode="list")
res <- vector(3, mode="list")
for (i in 1:3) {
ind <- setdiff(1:3, i)
buf_list[[i]] <- gBuffer(lt[ind,], width=200)
res[[i]] <- gDifference(lt[i, ], buf_list[[i]])
}
lapply(buf_list, plot, col="#FFFFFF90", add=TRUE)
lapply(res, plot, col="red", lwd=2, add=TRUE)
The current version of QGIS (QGIS 3.0+) has the option to Force segments to be exactly of a given length, except for the last one using v.split. v.split is accessed from the Processing Toolbox under GRASS --> Vector
Best Answer
[QGIS 2.8] Use the Intersect tool menu : "Vector / Geoprocessing tools / Intersect" (from Miro's answer in comments)
[QGIS 2.18] Use the Intersection Tool in the processing toolbox/panel :