Re: Numerical description of a contour
- To: mathgroup at smc.vnet.net
- Subject: [mg38780] Re: Numerical description of a contour
- From: "Allan Hayes" <hay at haystack.demon.co.uk>
- Date: Sun, 12 Jan 2003 06:16:58 -0500 (EST)
- References: <avjgd1$6ug$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Nicolas, I hope that the following will provide the data that you need For ContourPlot expr = x^2 + y^2; cg = ContourPlot[expr, {x, -1, 1}, {y, -1, 1}, ContourShading -> False]; The data here is a matrix of heights from which contour lines and contour shading is constructed, so convert the contour graphics into graphics which includes the contour lines explicitely. gr = Graphics[cg]; Extract the coordinates in the lines and add to each point {u,v} the value of expr for these values of x and y. cl = Cases[Graphics[cg], Line[lst_] :> (lst /. {u_Real, v_Real} -> {u, v, expr /. {x -> u, y -> v}}), Infinity]; This may do more than you need - note that the values of expr only approximate the intended contour height and that you can avoid adding the values if you plot the contour lines separately for specified heights. Anyway let's check: Show[Graphics3D[{Line /@ cl}]] For ContourPlot3D << "Graphics`ContourPlot3D`" No conversion is needed, and I will plot just one contour surface: gr3 = ContourPlot3D[x*y*z, {x, -1, 1}, {y, -1, 1}, {z, -1, 1}, Contours -> {0.1}] Extract the lists of points defining the polygons that make up the displayed surface. Cases[gr3, Polygon[lst_] :> lst, Infinity] 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 "Nicolas Fressengeas" <fresseng at ese-metz.fr> wrote in message news:avjgd1$6ug$1 at smc.vnet.net... > Dear Netters, > > In trying to analyse my 3D data with Mathematica, I want to visualize an > iso-surface. That is nicely done with ContourPlot in 2D and ContourPlot3D in > 3D. My aim is now to get a numerical description of these surfaces in order > to do them some numerical treatment. > > Any one to help me out ? > > Thanks in advance > > Nicolas > -- > ______________________________________________________ > Dr. Nicolas Fressengeas > http://www.ese-metz.fr/~fresseng > Supélec / Laboratoire Matériaux Optiques, Photonique et Systèmes > 2 rue E.Belin, 57070 METZ Cedex > Tel: +33 387 764 705 ... Fax: +33 387 764 700 > Plan d'accès:http://www.mappy.com/PlanPerso/fresseng/1 > > >