Re: Extracting contour values from ContourPlot

• To: mathgroup at smc.vnet.net
• Subject: [mg100873] Re: Extracting contour values from ContourPlot
• From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
• Date: Tue, 16 Jun 2009 21:55:21 -0400 (EDT)
• References: <h12gg4\$ect\$1@smc.vnet.net> <h13vp8\$8pm\$1@smc.vnet.net>

To build the legend it is necessary to determine the color Mathematica
used in the areas between the contour lines. Something like this then
draws the legend:

cols = Cases[plt, RGBColor[___], Infinity];
labels = Cases[plt, _Tooltip, Infinity] /. Tooltip[_, lbl_] :> lbl;
Graphics[
{
Riffle[cols, Table[Rectangle[{0, i}, {1, i + 1}], {i, Length
[cols]}]],
Table[Text[labels[[-i]], {1.5, i + 1}], {i, Length[labels]}]
}
]

I wonder whether color and labels will always be sorted in this
convenient order, though.

Cheers -- Sjoerd

On Jun 15, 1:06 am, Jens-Peer Kuska <ku... at informatik.uni-leipzig.de>
wrote:
> Hi,
>
> plt = ContourPlot[Cos[x*y], {x, -Pi, Pi}, {y, -Pi, Pi}];
>
> and
>
> Cases[plt, _Tooltip, Infinity] /. Tooltip[_, lbl_] :> lbl
>
> ?
>
> Regards
>    Jens
>
> dg wrote:
> > I have spent an hour researching this group and online, with no
> > definitive answer.
>
> > The problem: I have an nxm matrix of z values that I want to plot with
> > List(Contour|Density)Plot together with a legend that shows the
> > *actual* values of the contours used in the plot. (Seems like a pretty
> > basic thing to me....). I know how to draw a nice legend, that's not
> > the problem.
>
> > I have found a way to do it: I can specify the contours and plot range
> > explicitly. But what I really want is not to have to do this, and rely
> > on the semi-intelligent mechanism of Mathematica to pick an appropriate=
number
> > of contours and their values, THEN use those to draw the legend.
>
> > It seems that there is no way to do this. That is, there is no way to
> > extract the actual contour values used in the plot. I found a
> > ColorBarPlot package which however does not work in Mathematica 7:
> >   <http://library.wolfram.com/infocenter/MathSource/7030/>
>
> > Is it really not possible to do
> > this?

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