RE: Pick up coordinates along different contours.
- To: mathgroup at smc.vnet.net
- Subject: [mg43399] RE: [mg43382] Pick up coordinates along different contours.
- From: "David Park" <djmp at earthlink.net>
- Date: Fri, 29 Aug 2003 07:15:59 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Jun,
You can extract the points by digging into the graphics. Here is an example.
f[x_, y_] := x^2 + y^2
plot1 = ContourPlot[f[x, y], {x, -1.5, 1.5}, {y, -1.5, 1.5},
Contours -> {0.5, 1.0}, ContourShading -> False]
Now if we convert plot1 from ContourGraphics to Graphics we will obtain
Lines for the contours, which we can then extract using Cases.
clines = Cases[First[Graphics[plot1]], Line[_], Infinity]
You will notice that this contains a number of spurious lines that contain
only one point or the same point repeated. We can massage clines to get rid
of these cases.
clines2 =
clines /.
Line[{begin___List, a_List, b_List, end___List}] /;
Sqrt[(a - b).(a - b)] < 10.*^-10 -> Line[{begin, end}] /.
Line[{}] -> Sequence[] /. Line[{a_}] -> Sequence[]
Then you can extract the points themselves with
points = Cases[clines2, Line[pts_] -> pts, Infinity]
David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/
From: Jun Lin [mailto:jl_03824 at yahoo.com]
To: mathgroup at smc.vnet.net
I plot a couple of 2D contours by using ContourPlot. Now, I want to
pick up the coordinate of each point along each contour for next step
calculation purposes. I appreciate with your any suggestion of how to
get the coordinates of each point along a specific contour (suppose
two contours have been created).
Jun