Hello, You can use the function "circlefit" from "pracma". The example is adapted from the help page to fit your data.
#----------------------------------------------------------------------------------------------- require(pracma) xp <- c(113, 143, 184, 229, 290, 342, 393, 456, 540, 618) yp <- c(392, 389, 386, 383, 379, 380, 380, 380, 383, 388) rslt <- circlefit(xp, yp) x0 <- rslt[1]; y0 <- rslt[2]; r0 <- rslt[3] plot(c(100, 650), c(370, 400), type="n") grid() abline(h=0, col="gray"); abline(v=0, col="gray") points(xp, yp, col="darkred") w <- seq(0, 2*pi, len=1000) xx <- r0 * cos(w) + x0 yy <- r0 * sin(w) + y0 lines(xx, yy, col="blue") #----------------------------------------------------------------------------------------------- Hope this helps, Pascal 2013/9/19 Tom D. Harray <tomdhar...@gmail.com> > Hi there, > > I want to know the radius of curvature for a set of points, but cannot > figure out how to perform the fit in R. > > I have a set of points P_i for which I want to calculate the radius of > curvature. The coordinates (x_i|y_i) of the points in a data.frame: > > p <- data.frame( > x = c(113, 143, 184, 229, 290, 342, 393, 456, 540, 618), > y = c(392, 389, 386, 383, 379, 380, 380, 380, 383, 388) > ) > > For the radius of curvature I now have to find the circle the which > describes best my points. This circle has an origin at r_x and r_y, > and the radius r. The equation I started with is: > > r^2 = (r_x - x_i)^2 + (r_y + y_i)^2 > > r^2, r_x, and r_y are constant. Expanding the quadratic terms and > subtracting r^2 leads to > > 0 = x_i^2 + (-2*r_x)*x_i + y_i^2 + (-2*r_y)*y_i + r_x^2 + r_y^2 - r^2 > > The last three terms add up to zero due to r^2 = r_x^2 + r_y^2: > > 0 = x_i^2 + (-2*r_x)*x_i + y_i^2 + (-2*r_y)*y_i > > Here I got stuck. I -- as a non-mathematician -- would describe it as > quadratic equation in two dimensions, but I didn't succeed searching > for these terms in the help, mailing list, and web. > > My question is: How to estimate the r_x, and r_y from the set of > points p using R? > > > Thanks and regards, > > Dirk > > ______________________________________________ > 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. > -- Pascal Oettli Project Scientist JAMSTEC Yokohama, Japan [[alternative HTML version deleted]] ______________________________________________ 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.
