Calculating the length of a line created from a spatial intersect.
Walter,
Next time, please try to give as a simple self contained example in R
showing what you have done, and where you are stuck.
Here is how you can intersect lines and polygons, keeping their attributes:
library(raster)
library(rgeos)
# example data
p <- shapefile(system.file("external/lux.shp", package="raster"))
k1 <- (rbind(c(5.5, 49.6), c(6.5, 49.6)))
k2 <- (rbind(c(5.5, 50), c(6.5, 50)))
k <- SpatialLines(list(Lines(list(Line(k1)), "1"), Lines(list(Line(k2)), "2")))
k <- SpatialLinesDataFrame(k, data.frame(LID=1:2))
crs(k) <- crs(p)
# intersection
x <- intersect(k, p)
## note that x <- intersect(p, k)
## currently does not work; I'll fix that.
x
data.frame(x)
Robert
On Wed, Apr 1, 2015 at 8:18 AM, Walter Anderson <wandrson01 at gmail.com> wrote:
Hello all, I am continuing on the process of automating an analysis that I developed with ArcInfo using R with the sp, rgdal, rgeos, and raster libraries. This step is similiar to my previous question concerning calculating the area of a polygon created from a spatial intersect; however, the command I was referred doesn't perform the merge of the two data frames as it does when both spatial data sets are polygons. Here is the process I am using in ArcInfo that I need to replicate: I have a shape file (lines) that defines the limits of all of the projects with each project having a unique identifier. I have another shape file (lines) that represent the road centerlines and have a traffic volumen associated with each link. Process Step 1. I then buffer these project lines to create a second shape file that represents the 'footprint' of the project. (Creates polys). This is a small footprint (250 ft) that is solely used to associate the appropriate portion of any adjacent roadways. Mostly to accomodate spatial errors... Step 2. In ArcInfo, I perform an intersection of the two shape files (footprint and roadway centerlines) and this creates a third shape file which has a unique line for every project buffer/roadway intersection. This attribute table contains the attributes from both original shape files Step 3. I then perform a calculation that provides a weighted volume to associate with each project. The weighting is based upon the lengths of the road segments that are 'cut' by the project in relation to their original lengths. My issue is that I have not found a method to 'intersect' the two spatial data sets and retain both of their attributes (and calculate new lengths). Walter Anderson
_______________________________________________ R-sig-Geo mailing list R-sig-Geo at r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo