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Re: finding area in ListContourPlot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg116169] Re: finding area in ListContourPlot
  • From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
  • Date: Thu, 3 Feb 2011 05:39:09 -0500 (EST)
  • References: <iibdtk$nod$1@smc.vnet.net>

Hi Sam,

I'm not sure how you would define a 95% confidence interval in a
ListContourPlot, but assuming it is a given contour level value in
your contour plot here's an example of how you could do this.

I put it in separate steps for clarity, but you could do it in one
line. Please note that if you specify a certain contour level for
drawing you need curly brackets around it. So the syntax differs from
your skeleton example.

(*example data*)
ed = Flatten[
   Table[{x, y, Exp[-x^2 - 2 y^2]}, {x, -1, 1, .1}, {y, -1, 1, .1}],
   1];

(*plot*)
pl = ListContourPlot[ed, Contours -> {0.5}, ContourShading -> False] //
Normal;
(*Normal converts GraphicsComplex constructions to more useful
primitives with plain coordinates*)

(*finding point set*)
Cases[pl, Line[a___] -> a, Infinity]

Note that depending on your data set there may be more contour lines
and they need not be closed.

Now that you have the coordinates you can use the method described in
the link you specified to calculate the area.

Hope this helps.

Cheers -- Sjoerd


On Feb 2, 12:07 pm, Sam McDermott <samwell... at gmail.com> wrote:
> Hi-
>
> I'm new to the site, and I've searched around a bit for the solution to t=
his problem, but the answer doesn't seem too tractable. The nearest I've go=
tten was here:https://groups.google.com/forum/?fromgroups#!searchin/comp.so=
ft-sys.m...
>
> I would like to find the area bounded by the 95% confidence level of an o=
bject like <plotname>=ListContourPlot[<listname>,Contours->chimin+9.2]. I=
n the first place, I'm having trouble getting a list of the points that bou=
nd the contour region. I can use FullForm[<plotname>], followed by hunting =
through the (huge) FullForm output to do this, but I'd like to automate the=
 process since I'll have to do this operation for dozens of contour plots.
>
> Any help finding the area of region bounded in ListContourPlot or at leas=
t getting a list of points that define the region would be most appreciated=


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