获取日志空间中的边际线位置 [英] Get margin line locations in log space

问题描述

在上一个问题中，我问了如何获得用户坐标中的边界线位置.我以 line2user 函数的形式收到了一个很好的答案.但是，当 x 或 y 轴在对数刻度上时，我无法弄清楚如何修改该函数以使其工作.

In a previous question I asked how to get margin line locations in user coordinates. I received an excellent answer in the form of the line2user function. However, I cannot figure out how to modify the function to work when either the x or y axis is on a log scale.

我进行了一些修改以适应对数缩放轴:

I have made a couple modifications to accommodate a log-scaled axis:

line2user <- function(line, side, log = "") {
  lh <- par('cin')[2] * par('cex') * par('lheight')
  x_off <- diff(grconvertX(0:1, 'inches', 'user'))
  y_off <- diff(grconvertY(0:1, 'inches', 'user'))
  usr <- par('usr') ## Added by me
  if (grepl("x", log)) usr[1:2] <- 10^usr[1:2] ## Added by me
  if (grepl("y", log)) usr[3:4] <- 10^usr[3:4] ## Added by me
  switch(side,
         `1` = usr[3] - line * y_off * lh,
         `2` = usr[1] - line * x_off * lh,
         `3` = usr[4] + line * y_off * lh,
         `4` = usr[2] + line * x_off * lh,
         stop("Side must be 1, 2, 3, or 4", call.=FALSE))
}

但是，我无法弄清楚如何正确调整 xoff 和 yoff 变量以绘制正确的线条.插图:

However, I cannot figure out how to properly adjust the xoff and yoff variables to draw the proper lines. Illustration:

setup_plot <- function(log = "") {
  par(mar = c(2, 10, 2, 2), oma = rep(2, 4))
  plot.new()
  plot.window(xlim = c(1, 10), ylim = c(1, 10), log = log)
  box(which = "plot", lwd = 2, col = "gray40")
  box(which = "figure", lwd = 2, col = "darkred")
  box(which = "outer", lwd = 2, col = "darkgreen")
  text(x = 0.5, y = 0.5, 
       labels = "Plot Region", 
       col = "gray40", font = 2)
  mtext(side = 3, text = "Figure region", line = 0.5, col = "darkred", font = 2)
  mtext(side = 3, text = "Device region", line = 2.5, col = "darkgreen", font = 2)
  for (i in 0:9) {
    mtext(side = 2, col = "darkred", text = paste0("Line", i), line = i)
  }
}

setup_plot(log = "x")
abline(v=line2user(line=0:9, side=2, log = "x"), xpd=TRUE, lty=2)

考虑以下示例后，压缩行是有意义的:

The compressed lines make sense after considering the following example:

plot(10)
diff(grconvertX(0:1, 'inches', 'user'))
## [1] 0.08121573 (on my device)

plot(10, log = "x")
diff(grconvertX(0:1, 'inches', 'user'))
## [1] 0.0297354 (on my device)

在使用对数缩放轴时如何获得正确的 x_off 和 y_off 值?

How can I get the correct x_off and y_off values when working with a log-scaled axis?

推荐答案

这是一个适用于对数刻度和线性刻度轴的版本.诀窍是在 npc 坐标而不是 user 坐标中表示行位置，因为当轴在对数刻度上时，后者当然不是线性的.

Here's a version that works with log-scale and linear scale axes. The trick is to express line locations in npc coordinates rather than user coordinates, since the latter are of course not linear when axes are on log scales.

line2user <- function(line, side) {
  lh <- par('cin')[2] * par('cex') * par('lheight')
  x_off <- diff(grconvertX(c(0, lh), 'inches', 'npc'))
  y_off <- diff(grconvertY(c(0, lh), 'inches', 'npc'))
  switch(side,
         `1` = grconvertY(-line * y_off, 'npc', 'user'),
         `2` = grconvertX(-line * x_off, 'npc', 'user'),
         `3` = grconvertY(1 + line * y_off, 'npc', 'user'),
         `4` = grconvertX(1 + line * x_off, 'npc', 'user'),
         stop("Side must be 1, 2, 3, or 4", call.=FALSE))
}

这里有几个例子，用 mar=c(5, 5, 5, 5) 应用到你的 setup_plot:

And here are a couple of examples, applied to your setup_plot with mar=c(5, 5, 5, 5):

setup_plot()
axis(1, line=5)
axis(2, line=5)
abline(h=line2user(0:4, 1), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 2), lty=3, xpd=TRUE)
abline(h=line2user(0:4, 3), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 4), lty=3, xpd=TRUE)

setup_plot(log='x')
axis(1, line=5)
axis(2, line=5)
abline(h=line2user(0:4, 1), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 2), lty=3, xpd=TRUE)
abline(h=line2user(0:4, 3), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 4), lty=3, xpd=TRUE)

setup_plot(log='y')
axis(1, line=5)
axis(2, line=5)
abline(h=line2user(0:4, 1), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 2), lty=3, xpd=TRUE)
abline(h=line2user(0:4, 3), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 4), lty=3, xpd=TRUE)

setup_plot(log='xy')
axis(1, line=5)
axis(2, line=5)
abline(h=line2user(0:4, 1), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 2), lty=3, xpd=TRUE)
abline(h=line2user(0:4, 3), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 4), lty=3, xpd=TRUE)

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