The function crossing.psp() in the spatstat package might be of use. Here's an excerpt from its help page:
crossing.psp package:spatstat R Documentation Crossing Points of Two Line Segment PatternsDescription: Finds any crossing points between two line segment patterns. Usage: crossing.psp(A,B) -Don -- Don MacQueen Lawrence Livermore National Laboratory 7000 East Ave., L-627 Livermore, CA 94550 925-423-1062 On 11/22/11 12:48 PM, "R. Michael Weylandt <michael.weyla...@gmail.com>" <michael.weyla...@gmail.com> wrote: >If it's a one off, the identify() function might be of help -- if you >need something algorithmic it's harder due to floating point stuff and >sampling frequencies. Let me know if that's the case. > >Michael > >On Nov 22, 2011, at 3:40 PM, Monica Pisica <pisican...@hotmail.com> wrote: > >> >> >> >> Hi everyone, >> >> >> >> I am trying to get a point of intersection between a >> polyline and a straight line Š.. and get the x and y coordinates of >>this point. >> For exemplification consider this: >> >> >> >> >> >> set.seed(123) >> >> >> >> k1 <-rnorm(100, mean=1.77, sd=3.33) >> >> k1 <- sort(k1) >> >> q1 <- rnorm(100, mean=2.37, sd=0.74) >> >> q1 <- sort(q1, decreasing = TRUE) >> >> plot(k1, q1, xlim <- c((min(k1)-5), (max(k1)+5)), >> type="l") >> >> >> >> ya <- 2 >> >> xa = -5 >> >> yb=4 >> >> xb=12 >> >> >> >> lines(c(xa, xb), c(ya, yb), col = 2) >> >> >> >> # I want to get the x and y coordinates of the >> intersection of the 2 lines Š. >> >> >> >> m <- (ya-yb)/(xa-xb) >> >> b <- ya-m*xa >> >> ln <- loess(q1~k1) >> >> lines(ln) >> >> >> >> It is clear that the x, y will satisfy both linear >> equations, y = m*x + b and the ln polyline Š.. but while I can >>visualize the >> equation of the straight line I have problems with the polyline. I >>will appreciate >> any ideas to solve this problem. I thought it a trivial solution but it >>seems I >> cannot see it. >> Thanks, >> Monica >> >> >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >>http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. > >______________________________________________ >R-help@r-project.org mailing list >https://stat.ethz.ch/mailman/listinfo/r-help >PLEASE do read the posting guide >http://www.R-project.org/posting-guide.html >and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.