On Sep 26, 2011, at 11:03 AM, Chris82 wrote:
Dear R users,
I am thinking about an easy and especially fast solution to
calculate the
x,y coordinates of the interesection between the borders of the red
circle
and the line.
This would seem to be the solution to two simultaneous equations : one
a quadratic and the other linear. I suspect tenth-grade algebra would
be the level; Looking for something to minimize the mental strain also
succeeds easily. Googling on "intersection of line and circle"
produces this analytic approach (and there are many other webpages.)
http://mathworld.wolfram.com/Circle-LineIntersection.html
--
plot(c(-3,0,3,9,21),c(-8,0,5,12,25))
draw.circle(0,0,radius=6,border="red",col=NA,lty=1,lwd=1)
x <- c(-12,-6,-1,0,13,21)
y <- c(-19,-10,-5,0,9,25)
plot(x,y)
require(plotrix)
draw.circle(0,0,radius=6,border="red",col=NA,lty=1,lwd=1)
lines(c(-12,-6,-1,13,21),c(-19,-10,-5,9,25),cex=2)
At the moment I am interpolating the points which gives the basis
coordinates of the line. I do this with approx() and then I check
which
point is within the circle and which one is not. The probleme is,
that this
method is not really exact and for my dataset it takes too much time.
Thanks.
With best regards
--
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Sent from the R help mailing list archive at Nabble.com.
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