Re: [R] How to convert the "user coordinate system" in R graph to"normal coordinate system" whose origin is the upper-leftcornner of the drawing area?

From: Greg Snow <Greg.Snow_at_imail.org>
Date: Fri, 29 Feb 2008 09:32:59 -0700

Look at the cnvrt.coords function in the TeachingDemos package.

You should be able to use that function to transform from user coordinates to device coordinates (where 0 is left/bottom and 1 is right/top), then multiply the device coordinates by the resolution to get the pixel numbers.

Hope this helps,

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow_at_imail.org
(801) 408-8111
 
 


> -----Original Message-----
> From: r-help-bounces_at_r-project.org
> [mailto:r-help-bounces_at_r-project.org] On Behalf Of Guohui Ding
> Sent: Friday, February 29, 2008 12:12 AM
> To: R help (E-mail)
> Subject: [R] How to convert the "user coordinate system" in R
> graph to"normal coordinate system" whose origin is the
> upper-leftcornner of the drawing area?
>
> 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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>
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>
______________________________________________ R-help_at_r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Received on Fri 29 Feb 2008 - 16:50:45 GMT

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