MyEllipsefit

R package to fit an ellipse to data points. Convience wrapper around the conicfit package to provide ellipsis parameters (axes, angle, area, bounding box, and more). Offers an option to draw the ellipse as layer in ggplot2.

See

    help(package = "MyEllipsefit") 

for details on the function provided by this package.

See help(package = "conicfit")

for details on the conicfit package that provides the actual calculcations.

Function returns either a data frame with the fit parameters for the ellipse (Default). Or a list with two data frames, the fit parameters and the coordinates to draw the ellipse.

Fit parameters are:

• The X coordinate of the center of the ellipse.
• The Y coordinate of the center of the ellipse.
• The distance from the center to the perimenter along the major axis.
• The distance from the center to the perimenter along the minor axis.
• The tilt angle of the ellipse.
• The area of the ellipse.
• The goodnes-of-fit R2 of the ellipse fit.

If coords = TRUE, returns a data frame with the coordinates of the ellipse in addition.

If bbox = TRUE, in addition, returns a data frame with the extreme values of the coordinates of the bounding box for the ellipse.

Items are returned as a named list. See example below.

Installation

Installation straight from github (if package "devtools" is already installed) via

devtools::install_github("MarkusLoew/MyEllipsefit")

Example session

library(MyEllipsefit)

mydata <- data.frame(x = c(5.92, 5.37, 3.16, 0.71, -0.29, -1.14, -0.8291667, 4.14, 10.74, 18.97, 21.66,  21.57, 21.56, 23.15, 24.17, 24.10, 23.26, 19.39, 12.31, 6.11, 7.49, 5.79, 2.66, 1.01),
                     y = c(0.14, 0.14, 0.10, 0.08, 0.08, 0.08, 0.12, 0.22, 0.36, 0.43, 0.42, 0.42, 0.43, 0.42, 0.37, 0.32, 0.26, 0.20, 0.12, 0.10, 0.14, 0.11, 0.07, 0.05))

ell <- Ellipsefit(mydata, x, y, coords = TRUE, bbox = TRUE)

coord <- ell$Coord
bbox <- ell$Bbox
plot(y ~ x, data = mydata, ylim = c(0, 0.5), xlim = c(-2, 25))
lines(y ~ x, data = coord, col = "blue")
abline(v = bbox$x, h = bbox$y, col = "red")

# Calculate bounding box area to compare to ellipse area
bbox.area <- (bbox$x[2] - bbox$x[1]) * (bbox$y[2] - bbox$y[1])
area.ratio <- ell$Para$Area / bbox.area


# comparison with ggplot2::stat_ellipse
library(ggplot2)

p <- ggplot(mydata, aes(x = x, y = y))
 p <- p + geom_point()
 p <- p + stat_myell()
 p <- p + stat_ellipse(colour = "red")
p