geom_arc2() size parameter

[MartinMSPedersen]

I am trying to make a large red quarter circle using the code below.
I want the circle to have a width of 20.

1. Does the size parameter work correctly? Is size and width the same?
2. I expects the width same for the whole arc. It looks like it is wider to the left than to the bottom.
   

library(ggforce)
library(ggplot2)

l1 <- data.frame(x = c(0,50), y = c(30,30))
l2 <- data.frame(x = c(0,50), y = c(50,50))
l3 <- data.frame(x = c(30,30), y = c(0,50))
l4 <- data.frame(x = c(50,50), y = c(0,50))
a1 <- data.frame(x0 = 0, y0 = 0, r0 = 0, r = 40, angle = c(0, pi/2))

g <- ggplot()
g <- g + geom_arc2(data = a1, size = 80, color = "red",
                   aes(x0 = 0, y0 = 0, r = r, end = angle))
g <- g + geom_path(data = l1, aes(x,y))
g <- g + geom_path(data = l2, aes(x,y))
g <- g + geom_path(data = l3, aes(x,y))
g <- g + geom_path(data = l4, aes(x,y))
g <- g + coord_cartesian(expand = FALSE, xlim = c(-5, 55), ylim = c(-5, 55))
g

[thomasp85]

size (now linewidth) is the width of the line and is an absolute value not related to the coordinate system. if you want to control the width in relation to the coordinate system you can use geom_arc_bar()

l1 <- data.frame(x = c(0,50), y = c(30,30))
l2 <- data.frame(x = c(0,50), y = c(50,50))
l3 <- data.frame(x = c(30,30), y = c(0,50))
l4 <- data.frame(x = c(50,50), y = c(0,50))
a1 <- data.frame(x0 = 0, y0 = 0, r0 = 30, r = 50, angle = c(0, pi/2))

g <- ggplot()
g <- g + geom_arc_bar(data = a1, fill = "red", colour = NA,
                   aes(x0 = 0, y0 = 0, r0 = r0, r = r, start = 0, end = angle))
g <- g + geom_path(data = l1, aes(x,y))
g <- g + geom_path(data = l2, aes(x,y))
g <- g + geom_path(data = l3, aes(x,y))
g <- g + geom_path(data = l4, aes(x,y))
g <- g + coord_cartesian(expand = FALSE, xlim = c(-5, 55), ylim = c(-5, 55))
g