RE: [R] Using locator() to digitise

From: Mulholland, Tom <>
Date: Tue 22 Mar 2005 - 12:30:00 EST

I've used rimage to read in graphics files (jpeg.) If I recall correctly, I think I had to install some libraries. What I can't recall is if it was any faster than pixmap, as I was mainly concerned with the file format and the forensic image processing possibilities.


> -----Original Message-----
> From:
> []
> Sent: Monday, 21 March 2005 12:09 AM
> To:
> Subject: [R] Using locator() to digitise
> Hi Folks,
> I'm contemplating using locator() to digitise external
> graphics. To set context, I would be using X11 display
> on Linux.
> To pre-empt the obvious comment: I've found on the R site
> the suggestion to use the 'pixmap' package. I've tried
> this, and it works; but it involves building a big R
> object (the internal pixmap representation), and this
> chokes my somewhat puny laptop (e.g. it can take about
> 1 minute to draw the graphic inside a plot area using
> addlogo(), with mucho swappo, and subsequently working
> knee-deep in treacle). The following idea would be a lot
> slicker.
> For examples: I have something like
> a) A scatterplot of data printed in a journal (but the
> data values are not available;
> b) A contour map (on paper) of a region.
> So, I can scan the document, and obtain a file in some
> graphics format (jpeg, pbm or png, say).
> Now: an idea which I find attractive is to be able to
> overlay an R plot with axes onto a display of the graphics
> file (produced as an X window by any suitable program such
> as 'xv' or 'display') so that (if the overlay were possible)
> clicking on the points of the graphic would in fact be
> clicking on the R plot and, via locator(), generate the
> R-plot coordinates of the mouse clicks which would correspond
> to the selected points on the graphic.
> Provided the coordinate system of the R plot were properly
> related to the graphic, the results would be a digitisation
> of the selected points on the graphic.
> What seems to be needed for this idea to work is that
> the R-plot should be displayed in an X11() device whose
> background was completely transparent, so that when
> moved over the (independently generated) display of the
> graphic the latter would be visible (but locator() would
> still be working on the R-plot itself). Window resizing
> could look after the correspondence between graphic coordinates
> and R-plot coordinates.
> The R plot itself could be empty (apart from coordinate axes)
> or could contain "helper" elements such as grid lines, circles
> (e.g. I want to digitise graphics points within a certain circle),
> etc. "Helper" elements could be added to the R-plot by subsequent
> 'lines' or 'points' commands (e.g. I identify two points on
> the graphic, R-plot the line joining them, and then pick off
> graphic-points which lie on the R-line).
> So this question is really about producing a "bare" R plot
> on, as it were, a virtual acrylic transparency. It's certainly
> possible to do such a thing in X: e.g. the cute "xteddy" is
> in fact a picture of a bear on a completely transparent
> rectangular background, though you'd never know by looking!
> Any comments?
> With thanks, and best wishes to all,
> Ted.
> --------------------------------------------------------------------
> E-Mail: (Ted Harding) <>
> Fax-to-email: +44 (0)870 094 0861
> Date: 20-Mar-05 Time: 16:09:11
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> mailing list PLEASE do read the posting guide! Received on Tue Mar 22 12:34:02 2005

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