Coordinates for Named Plot Positions

Returns the xy-coordinates and text-adjustment values for named anchor positions such as "topleft", "center", etc., as used by legend(). Useful for placing text or other annotations at consistent, region-aware positions.

Usage

abcCoords(
  x = "topleft",
  region = c("plot", "figure", "device"),
  cex = NULL,
  inset = 0
)

Arguments

x

A character string specifying the anchor position. One of "bottomright", "bottom", "bottomleft", "left", "topleft", "top", "topright", "right", or "center". Partial matching is supported.

region

one of "plot" (default), "figure", or "device". Determines the coordinate region used. See Details for the clipping that comes with the latter two.

cex

character expansion factor. If NULL (default), the current par("cex") is used.

inset

inset distance from the boundary, specified in lines of text (character heights/widths). May be a scalar (applied to both x and y) or a length-2 vector (x inset, y inset). Default 0.

Value

A list with two components:

xy

A list with elements x and y giving the anchor coordinates in user space.

adj

A numeric vector of length 2, suitable for the adj argument of text().

Details

The positioning logic is adapted from legend(). The inset is computed in character units via strwidth() and strheight(), making it robust to device resizing, font changes, and plot-range scaling.

Three regions are supported:

"plot"

The inner plot area (par("usr")). The default, and the region legend() positions in.

"figure"

The figure region within the device, accounting for par("fig").

"device"

The full device area.

Coordinates for "figure" and "device" lie outside par("usr") and are therefore clipped away by text() and friends unless the drawing call sets xpd = NA. The returned values are in user space either way; only the clipping has to be turned off by the caller.

See also

text(), legend()

Other graphics.layout: axTicks, axisBreak(), isValidPlotRegion(), lineToUser(), mar(), plotFacet(), spreadOut()

Examples

plot(x = rnorm(10), type = "n", xlab = "", ylab = "")

# coordinates only
abcCoords("bottomleft")
#> $xy
#> $xy$x
#> [1] 0.64
#> 
#> $xy$y
#> [1] -2.580691
#> 
#> 
#> $adj
#> [1] 0 0
#> 

# place text at a named position
xy <- abcCoords("bottomleft")
text(x = xy$xy$x, y = xy$xy$y, labels = "My Label", adj = xy$adj)

# all nine positions with inset
sapply(c("topleft", "top", "topright",
         "left",    "center", "right",
         "bottomleft", "bottom", "bottomright"),
  function(p) {
    xy <- abcCoords(p, inset = 1)
    text(x = xy$xy$x, y = xy$xy$y,
         labels = p, adj = xy$adj)
  })
#> $topleft
#> NULL
#> 
#> $top
#> NULL
#> 
#> $topright
#> NULL
#> 
#> $left
#> NULL
#> 
#> $center
#> NULL
#> 
#> $right
#> NULL
#> 
#> $bottomleft
#> NULL
#> 
#> $bottom
#> NULL
#> 
#> $bottomright
#> NULL
#> 

# the margins need xpd = NA, whatever the coordinates say
xy <- abcCoords("bottomright", region = "figure", inset = 0.5)
text(x = xy$xy$x, y = xy$xy$y, labels = "source: ...",
     adj = xy$adj, cex = 0.7, xpd = NA)