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 [EMAIL PROTECTED] (801) 408-8111 > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] 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 > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@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. > ______________________________________________ R-help@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.
