cnvrt.coords: Convert between the 4 different coordinate sytems on a graphical device

Description

Takes a set of coordinates in any of the 4 coordinate systems (usr, plt, fig, or dev) and returns the same points in all 4 coordinate systems.

Usage

cnvrt.coords(x, y = NULL, input = c("usr", "plt", "fig", "dev"))

Arguments

Vector, Matrix, or list of x coordinates (or x and y coordinates), NA's allowed.

y coordinates (if x is a vector), NA's allowed.

input

Character scalar indicating the coordinate system of the input points.

Value

A list with 4 components, each component is a list with vectors named x and y. The 4 sublists are:
usrThe coordinates of the input points in usr (User) coordinates.
pltThe coordinates of the input points in plt (Plot) coordinates.
figThe coordinates of the input points in fig (Figure) coordinates.
devThe coordinates of the input points in dev (Device) coordinates.

Details

Every plot has 4 coordinate systems: usr (User): the coordinate system of the data, this is shown by the tick marks and axis labels. plt (Plot): Plot area, coordinates range from 0 to 1 with 0 corresponding to the x and y axes and 1 corresponding to the top and right of the plot area. Margins of the plot correspond to plot coordinates less than 0 or greater than 1. fig (Figure): Figure area, coordinates range from 0 to 1 with 0 corresponding to the bottom and left edges of the figure (including margins, label areas) and 1 corresponds to the top and right edges. fig and dev coordinates will be identical if there is only 1 figure area on the device (layout, mfrow, or mfcol has not been used). dev (Device): Device area, coordinates range from 0 to 1 with 0 corresponding to the bottom and left edges of the device (piece of paper, window on screen) and 1 corresponds to the top and right edges.

Examples

Run this code

old.par <- par(no.readonly=TRUE)

par(mfrow=c(2,2),xpd=NA)

# generate some sample data
tmp.x <- rnorm(25, 10, 2)
tmp.y <- rnorm(25, 50, 10)
tmp.z <- rnorm(25, 0, 1)

plot( tmp.x, tmp.y)

# draw a diagonal line across the plot area
tmp1 <- cnvrt.coords( c(0,1), c(0,1), input='plt' )
lines(tmp1$usr, col='blue')

# draw a diagonal line accross figure region
tmp2 <- cnvrt.coords( c(0,1), c(1,0), input='fig')
lines(tmp2$usr, col='red')

# save coordinate of point 1 and y value near top of plot for future plots
tmp.point1 <- cnvrt.coords(tmp.x[1], tmp.y[1])
tmp.range1 <- cnvrt.coords(NA, 0.98, input='plt')

# make a second plot and draw a line linking point 1 in each plot
plot(tmp.y, tmp.z)

tmp.point2 <- cnvrt.coords( tmp.point1$dev, input='dev' )
arrows( tmp.y[1], tmp.z[1], tmp.point2$usr$x, tmp.point2$usr$y,
 col='green')

# draw another plot and add rectangle showing same range in 2 plots

plot(tmp.x, tmp.z)
tmp.range2 <- cnvrt.coords(NA, 0.02, input='plt')
tmp.range3 <- cnvrt.coords(NA, tmp.range1$dev$y, input='dev')
rect( 9, tmp.range2$usr$y, 11, tmp.range3$usr$y, border='yellow')

# put a label just to the right of the plot and 
#  near the top of the figure region.
text( cnvrt.coords(1.05, NA, input='plt')$usr$x,
	cnvrt.coords(NA, 0.75, input='fig')$usr$y,
	"Label", adj=0)

par(mfrow=c(1,1))

## create a subplot within another plot

plot(1:10, 1:10)

tmp <- cnvrt.coords( c( 1, 4, 6, 9), c(6, 9, 1, 4) )

par(plt = c(tmp$dev$x[1:2], tmp$dev$y[1:2]), new=TRUE)
hist(rnorm(100))

par(fig = c(tmp$dev$x[3:4], tmp$dev$y[3:4]), new=TRUE)
hist(rnorm(100))

par(old.par)




## The function is currently defined as
function(x,y=NULL,input=c('usr','plt','fig','dev')) {

  input <- match.arg(input)
  xy <- xy.coords(x,y)
  
  cusr <- par('usr')
  cplt <- par('plt')
  cfig <- par('fig')
  
  if(input=='usr'){
    usr <- xy
    
    plt <- list()
    plt$x <- (xy$x-cusr[1])/(cusr[2]-cusr[1])
    plt$y <- (xy$y-cusr[3])/(cusr[4]-cusr[3])

    fig <- list()
    fig$x <- plt$x*(cplt[2]-cplt[1])+cplt[1]
    fig$y <- plt$y*(cplt[4]-cplt[3])+cplt[3]

    dev <- list()
    dev$x <- fig$x*(cfig[2]-cfig[1])+cfig[1]
    dev$y <- fig$y*(cfig[4]-cfig[3])+cfig[3]

    return( list( usr=usr, plt=plt, fig=fig, dev=dev ) )
  }

  if(input=='plt') {

    plt <- xy

    usr <- list()
    usr$x <- plt$x*(cusr[2]-cusr[1])+cusr[1]
    usr$y <- plt$y*(cusr[4]-cusr[3])+cusr[3]

    fig <- list()
    fig$x <- plt$x*(cplt[2]-cplt[1])+cplt[1]
    fig$y <- plt$y*(cplt[4]-cplt[3])+cplt[3]

    dev <- list()
    dev$x <- fig$x*(cfig[2]-cfig[1])+cfig[1]
    dev$y <- fig$y*(cfig[4]-cfig[3])+cfig[3]

    return( list( usr=usr, plt=plt, fig=fig, dev=dev ) )
  }

  if(input=='fig') {

    fig <- xy

    plt <- list()
    plt$x <- (fig$x-cplt[1])/(cplt[2]-cplt[1])
    plt$y <- (fig$y-cplt[3])/(cplt[4]-cplt[3])

    usr <- list()
    usr$x <- plt$x*(cusr[2]-cusr[1])+cusr[1]
    usr$y <- plt$y*(cusr[4]-cusr[3])+cusr[3]

    dev <- list()
    dev$x <- fig$x*(cfig[2]-cfig[1])+cfig[1]
    dev$y <- fig$y*(cfig[4]-cfig[3])+cfig[3]
    
    return( list( usr=usr, plt=plt, fig=fig, dev=dev ) )
  }

  dev <- xy

  fig <- list()
  fig$x <- (dev$x-cfig[1])/(cfig[2]-cfig[1])
  fig$y <- (dev$y-cfig[3])/(cfig[4]-cfig[3])

  plt <- list()
  plt$x <- (fig$x-cplt[1])/(cplt[2]-cplt[1])
  plt$y <- (fig$y-cplt[3])/(cplt[4]-cplt[3])

  usr <- list()
  usr$x <- plt$x*(cusr[2]-cusr[1])+cusr[1]
  usr$y <- plt$y*(cusr[4]-cusr[3])+cusr[3]

  return( list( usr=usr, plt=plt, fig=fig, dev=dev ) )

  }