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MathGroup Archive 1999

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Re: Contourline values

  • To: mathgroup at smc.vnet.net
  • Subject: [mg20034] Re: Contourline values
  • From: "Kevin J. McCann" <kevinmccann at Home.com>
  • Date: Sat, 25 Sep 1999 18:46:03 -0400
  • Organization: @Home Network
  • References: <7se5tl$qrp@smc.vnet.net> <7sho0u$1jq@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Allan,

I had a look at your example and wonder if you could elaborate a bit on what
happened.  If I look at cg with FullForm, I get  stuff like:

cg = ContourPlot[1/((x - 1)(x + 1)), {x, -2, 2}, {y, 0, 1},ContourShading ->
False, Contours -> 3];

cg//FullForm

Produces:
ContourGraphics[List[List[0.333333, 0.515789, ...


On the other hand

Graphics[cg]//FullForm

Produces:

Graphics[List[
    List[GrayLevel[0.], AbsoluteThickness[0.5],
      Line[List[List[1.37445, 1.], List[1.37445, 0.928571],...

I don't see the correlation.  In particular, I don't see how the first {x,y}
point in the Line, viz. {1.37445,1.}, is produced from the earlier
ContourGraphics.

Thanks,

Kevin


Allan Hayes <hay at haystack.demon.co.uk> wrote in message
news:7sho0u$1jq at smc.vnet.net...
>
> Rita Bijlsma <R.Bijlsma at iri.tudelft.nl> wrote in message
> news:7se5tl$qrp at smc.vnet.net...
> > Hi!
> >
> >   I can not find a way to get contourline values in contour plots.
> >
> >   Can it be done (automatically) ?
> >
> >                                    Thanks!
> >                                             Rita
> >
> > --
> >   .-. || Drs. Rita Bijlsma                 tel: +31-15-2787109
> >  /   \|| IRI dept of Radiation Physics     fax: +31-15-2786422
> >  |   ||| Delft University of Technology  email: rita at iri.tudelft.nl
> >  |   |||_The Netherlands ______________ http://www.iri.tudelft.nl/~rita
> >
>
> Rita,
>
> cg = ContourPlot[1/((x - 1)(x + 1)), {x, -2, 2}, {y, 0, 1},
>       ContourShading -> False, Contours -> 3];
>
> ContourGraphics[]
>
>
> Contour graphics stores a matriex of heights - no explicit lines. To get
the
> lines we convert the contour graphics object to a Graphics object and then
> use Cases to gert a list of the result of passing the first point
> coordinates for each line to the expression being plotted. Since there may
> be, as here, more than one line at the same height, we then use Union to
> remove duplicates.
>
> Cases[Graphics[cg],
>     Line[{{x_, y_}, ___}] :> (1/((x - 1)(x + 1))),
>     Infinity] // Union
>
>
> Out[28]=
> {-10175.9, -10175.9, -7.48556, -7.48556, -1.63844, -1.63844, 1.1247,
1.1247,
> \
> 6.99341, 6.99341}
>
>
> --
> Allan
> ---------------------
> Allan Hayes
> Mathematica Training and Consulting
> Leicester UK
> www.haystack.demon.co.uk
> hay at haystack.demon.co.uk
> Voice: +44 (0)116 271 4198
> Fax: +44 (0)870 164 0565
>
>
>



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