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MathGroup Archive 2007

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Re: Reading Coordinates from Plot

  • To: mathgroup at
  • Subject: [mg80166] Re: Reading Coordinates from Plot
  • From: Albert <awnl at>
  • Date: Tue, 14 Aug 2007 06:59:15 -0400 (EDT)
  • References: <> <f9p564$r44$>


> The following code, based upon some posts of "Albert" to that thread, 
> allows you to click points ONLY on the graph of the function and see the 
> coordinates of that point below the plot, where from which you can copy 
> the current coordinate pair and paste it elsewehere. Unfortunately, as 
> it stands it does not allow you to produce all at once, and hence to 
> copy, all the points you've clicked.
>    trackPointOnPlot[f_,{a_,b_},strt_: Automatic]:=
>      Module[
>        {start=strt/.Automatic->a},DynamicModule[{p={start,f[start]}},
>        Column[{
>          LocatorPane[Dynamic[p,(p={First@#,f[First@#]})&],
>            Plot[f[x],{x,a,b}]],
>          Dynamic[p]
>        }]
>      ]
>    ]
>    (* examples to try *)
>    trackPointOnPlot[Cos,{0,10},Pi]
>    trackPointOnPlot[Cos,{0,10}]

Murray mentioned my code which was actually written for a slightly 
different problem.

Since I was missing the behavior myself, I made another attempt to mimic 
the original V5 behavior. Still this does not give a good answer why 
something like that isn't provided with Mathematica in the first place. 
Also worth a note is that with <<Version5`Graphics` one can get the old 
behavior, including the reading off of coordinates.

The function below can be wrapped around any 2d Graphics-Object and 
should work with most, a simple example usage is shown after the 
definition. It shows you the coordinates of where your mouse position 
sits and when clicking appends the coordinates to a list which is copied 
to the clipboard. The copy to clipboard functionality can probably be 
done better, what I came up with is rather a kind of workaround. Also I 
have not found a possibility to get the information of whether the 
Alt-Key is hold on the keyboard, that functionality seems to be limited 
to regular letters and some more, according to the docs. I wonder why 
this limitation has been necessary and irritated as I am :-) I don't 
make use of any keyboard events at all...

Well, here is the code:

ShowAndGetCoordinates[g_Graphics] := Deploy[DynamicModule[{
     coords = {Indeterminate, Indeterminate},
     collected = {},
     copytoclipboard = Function[
        nb = CreateDocument[ExpressionCell[#], Visible -> False];
        SelectionMove[nb, Before, Notebook];
        SelectionMove[nb, Next, Cell];
        SelectionMove[nb, All, CellContents];
        FrontEndTokenExecute[nb, "Copy"];
           Dynamic[Point /@ collected]}]],
         "MouseMoved" :> (coords = MousePosition["Graphics"]),
         "MouseClicked" :> (
            coords = MousePosition["Graphics"];
            AppendTo[collected, coords];
            Dynamic[ToString@NumberForm[coords[[1]], {10, 2}]], String,
             Enabled -> False, ImageSize -> 170], "x", Left],
            Dynamic[ToString@NumberForm[coords[[2]], {10, 2}]], String,
             Enabled -> False, ImageSize -> 170], "y", Left],
          Button["Reset", copytoclipboard[collected = {}],
           ImageSize -> 70]

Example Usage:

  Plot[Sin[x], {x, 0, Pi}, PlotStyle -> Red, ImageSize -> 500,
   Frame -> True]]

Or, if you prefer to see this in an extra window:

   Plot[Sin[x], {x, 0, \[Pi]}, PlotStyle -> Red, ImageSize -> 500,
    Frame -> True]]

Of course, like always, appearance is a matter of taste and there is 
room for improvement, so let me know if you have some...



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