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

问题描述

在一个上一个问题中，我问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轴或y轴处于对数刻度时，我无法弄清楚如何修改该功能以使其工作.

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.

我做了一些修改以适应对数刻度轴:

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)

在考虑以下示例后，压缩线才有意义:

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)

使用对数刻度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

这是可与对数刻度和线性刻度轴配合使用的版本.诀窍是用npc坐标而不是user坐标表示线位置，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))
}

以下是一些示例，它们通过mar=c(5, 5, 5, 5)应用于您的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)

这篇关于获取日志空间中的边距线位置的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！