x, y for point of intersection
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 <pisicandru at hotmail.com> wrote:
Hi everyone,
I am trying to get a point of intersection between a
polyline and a straight line ?.. 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 ?.
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 ?.. 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
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