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grid package and lines

Paul Murrell 
Hi
"Willemsen, Sten" wrote:
I think you are getting bitten by the fact that the locations for
drawing points and lines can be specified in a number of different
coordinate systems.  There is a default coordinate system for each
graphical primitive;  for points the default is "native" which means
that points are drawn relative to the x-scale and y-scale of the current
viewport, but for lines the default is "npc" which means that lines are
drawn relative to a "normalised" coordinate system [bottom-left corner
of the viewport is (0,0), top-right corner is (1,1)].  The defaults are
there so that you can ignore the use of "units" to specify a coordinate
system in some cases, but if the default isn't what you want then you
will have to get your hands dirty :)  [Complaints about selection of
inappropriate default units should be directed to me :(]

I hope the following example (comments included) helps to show what is
going on ...

    library(grid)
    x <- rnorm(10)
    y <- rnorm(10)
    push.viewport(plotViewport(c(5, 5, 3, 2)))
    push.viewport(dataViewport(x, y))
    grid.rect(gp=gpar(lty="dashed"))
    grid.xaxis()
    grid.yaxis()
    # default units for grid.points are "native"
    grid.points(x, y)
    # can specify other units
    grid.points(c(0, 0, 1, 1),
                c(0, 1, 1, 0),
                default.units="npc",
                pch=16)
    # default units for grid.lines are "npc"
    grid.lines(c(0, 0.5, 1, 0.5, 0),
               c(0.5, 1, 0.5, 0, 0.5),
               gp=gpar(col="green"))
    # can specify other units
    grid.lines(unit(x, "native"),
               unit(y, "native"))
    

Paul

Thread (3 messages)

Willemsen, Sten grid package and lines Nov 27 Deepayan Sarkar grid package and lines Nov 27 Paul Murrell grid package and lines Nov 27