MaplePrimes - answers and comments on Question, How to extract data from a contour plot?

By getdata command

Markiyan Hirnyk — Tue, 09 Oct 2012 12:11:31 Z

It can be done as follows.
> p := contourplot(x*F1, x = -3 .. 3, eta = -.2 .. .2):
> d := [plottools:-getdata(p)];
> nops(d);

664
> a := [seq(convert(d[j, 3][1], list), j = 1 .. 664),
seq(convert(d[j, 3][2], list), j = 1 .. 664)]:
#We skip the unnecessary information in the list d, remaining only the coordinates of the points.
#Because these are stored as Vectors, we convert the ones to lists. You may order a in need.
> writedata("c:/data.txt", a);

But why do it?

Preben Alsholm — Tue, 09 Oct 2012 12:38:09 Z

I wonder why you would want to do it, but certainly getdata will get you the data:

contourplot(x*F1,x=-3..3,eta=-0.2..0.2);
dat:=plottools:-getdata(%):
dm:=op(op~(3,[dat])):
M:=<dm>;
#Notice that if you plot M by plot(M); you get connecting lines unless you ask for style=point, whereas plotting [dm] doesn't.
plot([dm]);
#You can use ExportMatrix to export M and ImportMatrix to get it back. The sequence dm is easily recovered from M:
dm[1..10];
seq(M[i..i+1,1..2],i=1..20,2);

increase grid size

Christopher2222 — Tue, 09 Oct 2012 17:00:13 Z

It is good you used grid=[100,100] as the default is 25 but why don't you increase your grid size to 1000 or more? That should increase your resolution.

Also maybe use contours=# option to fix the number of contours being drawn.

The reason

J4James — Tue, 09 Oct 2012 13:37:44 Z

First of all, I would like to thank both of you (@Markiyan Hirnyk and @Preben Alsholm) .

The reason is that I use another software for just plotting purpose,

which gives me a very nice visual results.

The problem is that the output produced by maple is not that good

(maybe bcoz of my lack of understanding).

Forexample

contourplot(p(x)(y),x=-4.0..4,y=-1.5..1.5,grid=[100,100]);

Here you can see, the output is not that clear. And I do not know how to choose

a more visible color and also how to change the labels and to make it more bright.

P.S. As you mentined about the "connecting lines", bcoz of that I can not use the

data more freely (restricted to point style).

Not restricted to point style

Preben Alsholm — Tue, 09 Oct 2012 16:21:09 Z

@J4James You are restricted to point style only if you plot M as is. And that would only be relevant if you imported M from a file. But then, as I said, you can recover the sequence dm, which was constructed directly from the plot data.

memory allocation problem

J4James — Wed, 10 Oct 2012 07:13:04 Z

@Christopher2222 As you suggested, I have increased the grid size and it gives me a

more clear result. There is a problem of memory allocation, whenever I go beyond

[500,500]. But this time the results are very good.

contourplot(p(x)(y),x=-4.0..4,y=-1.5..1.5,grid=[400,400],

contours=25,color=black,labels=["x","y"]);

I choose to export the fig from maple as .eps, which gives a better visual output.

Thanks