Dear friends,

      The user coordiante system in the R graphics is easy to understand as
it simply corresponds to the range of values on the axes of the plot.
However, sometimes, we want to kown the coordinates of a region in other
system, e.g., the normal coordinate system whose origin is the the
upper-left cornner of the drawing area which is used to set the hot regions
in the HTML image maps. Is there any suggestion?

     For example, I execute the code,

> png("x.png",  width = 480, height = 480,
+     pointsize = 12, bg = "white", res = 100);
> plot(0, xlim=c(0, 100), ylim = c(0,100), type="n")
> rect(0, 0, 100, 100)
> points(0, 0, col = 'red')
> dev.off()

I will get a figure named "x.png". The resolution of this figure is 100 dpi
and the width and height are 480 pixels when I opened it with Photoshop.
When I move the cursor to the point drawed by points(0, 0, col = 'red'), I
can find the position of this point is about (87, 376) [(x, y)]. I want to
know how to convert the (0, 0) in the user coordinate system to this value?

I look forward to hearing from you.

-- 
ADDRESS: Bioinformatics Center, Shanghai Institutes for Biological Sciences,
Chinese Academy of Sciences
320 Yueyang Road, Shanghai 200031, P.R.China
TELEPHONE: 86-21-54920086

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