R help - Nov 2002 - grid package and lines

Hello list,

When using the grid package in R 1.60 under windows grid.lines and
grid.line.to seem not to use the coordinate system as defined by the current
viewport whereas grin.points does. Am I doing something wrong?

Sten
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On Wednesday 27 November 2002 05:27 am, Willemsen, Sten
wrote:
> Hello list,
>
> When using the grid package in R 1.60 under windows grid.lines and
> grid.line.to seem not to use the coordinate system as defined by the
> current viewport whereas grin.points does. Am I doing something wrong?
?grid.points says:

Usage:

     grid.points(x = unit(runif(10), "native"),
                 y = unit(runif(10), "native"),
                 pch = 1, size = unit(1, "char"),
                 default.units = "native", 
                                 ^^^^^^^^
                 gp=gpar(), draw = TRUE, vp = NULL)


?grid.lines says:

Usage:

     grid.lines(x = unit(c(0, 1), "npc", units.per.obs),
            y = unit(c(0, 1), "npc", units.per.obs), 
            default.units = "npc", units.per.obs = FALSE,
                            ^^^^^
            gp=gpar(), draw = TRUE, vp = NULL)

Nothing you have said seems to contradict this. If you want grid.lines to use 
the native coordinate system, use 'default.units = "native"'

Deepayan




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Hi


"Willemsen, Sten" wrote:
> 
> Hello list,
> 
> When using the grid package in R 1.60 under windows grid.lines and
> grid.line.to seem not to use the coordinate system as defined by the
current
> viewport whereas grin.points does. Am I doing something wrong?

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
-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x5392
paul at stat.auckland.ac.nz
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