interactive 2-D plot interrogation

Greetings Friends:

I am trying to find a widget or some other method to let me interrogate a 
2-D image using the mouse.  I have a data.frame that I can visualize using
image() in R.  I would like to point to a pixel and have its coordinates
displayed.

I've read Peter Dalgaard's primer on R-Tcl/Tk, R-News, 1(3):27-31, and his
update R-News2(3):25-27, but am still struggling. 

Can anyone suggest a method for interactively interrogating of a 2-D image?

Look at the InteractiveTkrPlot example on James Wettenhall's site:
http://bioinf.wehi.edu.au/~wettenhall/RTclTkExamples/InteractiveTkrPlot.html

His example is over discrete set of points, which you can adapt to find the
location with respect to curves or lines (which I did at work, where I can't
get to right now).

The key is that the 'widget' you bind to an event (like left-Mouse in his
example) get (x,y) pixel coordinates from the system which given appropriate
information from par() can be translated into your data coordinates in just
a few steps.

James' site is a treasure chest for R and tcltk. Highly recommended.

Hope this helps, Dirk

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