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### finding area in ListContourPlot

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Hi-

I'm new to the site, and I've searched around a bit for the solution to this problem, but the answer doesn't seem too tractable. The nearest I've gotten was here: https://groups.google.com/forum/?fromgroups#!searchin/comp.soft-sys.math.mathematica/finding\$20area\$20of\$20a\$20contour\$20region/comp.soft-sys.math.mathematica/Hs6KIWL3fvE/DnZQm6joE0gJ

I would like to find the area bounded by the 95% confidence level of an object like <plotname>=ListContourPlot[<listname>,Contours->chimin+9.2]. In the first place, I'm having trouble getting a list of the points that bound 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 least getting a list of points that define the region would be most appreciated.

Thanks very much,
Sam

 0

See related articles to this posting

Use Cases to extract points.

plot = ListContourPlot[
Table[Sin[x] Sin[y], {x, -3, 3, 0.1}, {y, -3, 3, 0.1}],
Contours -> 7]
points = Cases[plot, GraphicsComplex[x__] :> {x}, Infinity];

I'm not sure how you'll isolate precisely the points you want, but that's
a start.

Bobby

On Wed, 02 Feb 2011 05:07:24 -0600, Sam McDermott <samwell187@gmail.com>
wrote:

> Hi-
>
> I'm new to the site, and I've searched around a bit for the solution to
> this problem, but the answer doesn't seem too tractable. The nearest
> I've gotten was here:
>
> I would like to find the area bounded by the 95% confidence level of an
> object like <plotname>=ListContourPlot[<listname>,Contours->chimin+9.2].
> In the first place, I'm having trouble getting a list of the points that
> bound 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
> least getting a list of points that define the region would be most
> appreciated.
>
> Thanks very much,
> Sam
>

--
DrMajorBob@yahoo.com

 0

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

(*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...@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=
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=
..
>
> Thanks very much,
> Sam

 0

Thanks so much for the help! This seems to extract everything in the
correct way.

All the best,
Sam

 0