I have a plot with three curves. x is a function of v. Is there a way to extract a table of the all of the coordinates on the plot? I am specifically looking for a way to find the average [x] value and the average [y] value for each curve. Open in Wolfram Cloud ↗

Something like this perhaps (for your first function)? c1 = 1.01/.01 f1[v_, x_] := v^2/2 + c1 ((.7/(v x^2))^.01 - 1) - 1 xvals = Table[{v, x /. FindRoot[f1[v, x] == 0, {x, 1}]}, {v, .2, 2.5, .2}] ListLinePlot[xvals]

That did not work. I need to find a way to create a table with the x and v values from the curves so I can find the average for each curve. Open in Wolfram Cloud ↗

The points for each line can be extracted from the ContourPlot. p3 = ContourPlot[{v^2/2 + 1.01/(1.01 - 1) ((0.7/(v x^2))^(1.01 - 1) - 1) == 1/x, v^2/2 + 1.01/(1.01 - 1) ((1.092/(v x^2))^(1.01 - 1) - 1) == 1/x, v^2/2 + 1.01/(1.01 - 1) ((1.3/(v x^2))^(1.01 - 1) - 1) == 1/x}, {x…

How do I extract the coordinates?

Don’t understand the question, the list linepoints has the {x, y} coordinates. linePoints[[1]] gives the coordinates for the first plot, etc.

Hello Rohit. Coool. Do you have any idea what is the purpose of that polygon-stuff? Greetings, HD P.S. I made an error when copying the 1st function ( right hand side 1 instead 1/x). With the correct formula FindRoot doesn’t work. I really wonder how they find these contours…

Hi Hans, If you look at InputForm@p3 there is a GraphicsComplex with a list of coordinates. Those coordinates correspond to all of the points in the plot. Further down there are 6 Line, each with a list of integers. Is that what you mean by “polygon-stuff”? These integers are indexes into the Graph…

Hello Rohit, thank you very much. I know how GraphicsComplex works. What I meant was plt = ContourPlot[x^2 + y^2, {x, -2, 2}, {y, -2, 2}, Contours -> {1}] points = Cases[plt, GraphicsComplex[pts___] :> pts, Infinity]; lineIndexes = plt // Cases[#, Line[idx___] :> idx, Infinity] &; nps = Flatten[l…

I need to find a way to create a table with the x and v values from the curves so I can find the average for each curve. Finding this average is a nice problem for its own sake! One cannot just use the coordinates of these points and calculate its mean, because they are not necessarily equally sp…

Finding [x] and [y] coordinates on curves.

Questions

henrikschachner (Henrik Schachner) December 21, 2021, 5:52pm 15

This appears to be somewhat related to this old post:
Is there a problem with ContourPlot[] function?

One just needs the option Mesh -> All:

ContourPlot[x^2 + y^2, {x, -2, 2}, {y, -2, 2}, Contours -> {1, 2.2}, 
 Mesh -> All]

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Finding [x] and [y] coordinates on curves.

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