From nils106 at googlemail.com  Wed Nov  6 06:41:55 2019
From: nils106 at googlemail.com (Nils Wagner)
Date: Wed, 6 Nov 2019 12:41:55 +0100
Subject: [Matplotlib-users] Extract the x- and y-locations from the contour
 matrix C
Message-ID: <CAE7vhgN0cKXf54hvgT4Y=up_vYFL-o=w=ChSWUBNBMDnZ-nCPQ@mail.gmail.com>

Hi All,

in Octave you can do something like this

% Define the input grid
[x, y] = meshgrid(linspace(-2, 2));
% Calculate the two surfaces
%z1 = y.^2 + 2*x;
z1 = exp(-(x.^2 + y.^2));
%z2 = 2*y.^3 - x.^2;
z2 =  0.4+0.0*x+0.0*y;
% Visualize the two surfaces
figure(1);
surface(x, y, z1, 'FaceColor', [0.5 1.0 0.5], 'EdgeColor', 'none');
surface(x, y, z2, 'FaceColor', [1.0 0.5 0.0], 'EdgeColor', 'none');
view(3); camlight; axis vis3d
% Take the difference between the two surface heights and find the contour
% where that surface is zero.
zdiff = z1 - z2;
%C = contours(x, y, zdiff, [0 0]);
figure(2);
contour(x, y, zdiff, [0 0]);
C = contour(x, y, zdiff, [0 0]);
% Extract the x- and y-locations from the contour matrix C.
xL = C(1, 2:end)
yL = C(2, 2:end)
% Interpolate on the first surface to find z-locations for the intersection
% line.
zL = interp2(x, y, z1, xL, yL);
% Visualize the line.
figure(3);
line(xL, yL, zL, 'Color', 'k', 'LineWidth', 3);

How can we extract the x- and y-locations from the contour matrix C in
matplotlib?
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From jslavin at cfa.harvard.edu  Wed Nov  6 15:13:43 2019
From: jslavin at cfa.harvard.edu (Slavin, Jonathan)
Date: Wed, 6 Nov 2019 15:13:43 -0500
Subject: [Matplotlib-users] Extract the x- and y-locations from the
 contour matrix C
In-Reply-To: <mailman.44.1573059604.12249.matplotlib-users@python.org>
References: <mailman.44.1573059604.12249.matplotlib-users@python.org>
Message-ID: <CACcRS=fykjZM57H5Wuf-q7cdt3Bs4pJ-qKSHcApNQTMsy4NTGQ@mail.gmail.com>

Hi Nils,

Extracting the x and y locations from a contour is a bit of a pain in
matplotlib (or at least was last time I tried it). if you do something like
c = ax.contour(x,y,z,...)
(where ... stands in for the arguments you might want to supply)
then c is a QuadContourSet. To get at the contour data you need to do
something like
p = c.collections[i].get_paths()
(if you want the i'th collection, i.e. contour level number i, or you could
iterate of c.collections)
then p is a list of Path objects corresponding to each separate contour.
p.vertices is then an N x 2 array of the x and y values

An alternative to this is to use scikit-image package, in particular
skimage.measure.find_contours. However in that case you do something like:
c = find_contours(image,level)
(where image is a 2D array) and you get back a list of (n,2) arrays with
the indices of the image for the contour. To get the x,y values then you
need to scale those indices accordingly.

Jon

> Date: Wed, 6 Nov 2019 12:41:55 +0100
> From: Nils Wagner <nils106 at googlemail.com>
> To: matplotlib-users at python.org
> Subject: [Matplotlib-users] Extract the x- and y-locations from the
>         contour matrix C
> Message-ID:
>         <CAE7vhgN0cKXf54hvgT4Y=up_vYFL-o=w=
> ChSWUBNBMDnZ-nCPQ at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi All,
>
> in Octave you can do something like this
>
> % Define the input grid
> [x, y] = meshgrid(linspace(-2, 2));
> % Calculate the two surfaces
> %z1 = y.^2 + 2*x;
> z1 = exp(-(x.^2 + y.^2));
> %z2 = 2*y.^3 - x.^2;
> z2 =  0.4+0.0*x+0.0*y;
> % Visualize the two surfaces
> figure(1);
> surface(x, y, z1, 'FaceColor', [0.5 1.0 0.5], 'EdgeColor', 'none');
> surface(x, y, z2, 'FaceColor', [1.0 0.5 0.0], 'EdgeColor', 'none');
> view(3); camlight; axis vis3d
> % Take the difference between the two surface heights and find the contour
> % where that surface is zero.
> zdiff = z1 - z2;
> %C = contours(x, y, zdiff, [0 0]);
> figure(2);
> contour(x, y, zdiff, [0 0]);
> C = contour(x, y, zdiff, [0 0]);
> % Extract the x- and y-locations from the contour matrix C.
> xL = C(1, 2:end)
> yL = C(2, 2:end)
> % Interpolate on the first surface to find z-locations for the intersection
> % line.
> zL = interp2(x, y, z1, xL, yL);
> % Visualize the line.
> figure(3);
> line(xL, yL, zL, 'Color', 'k', 'LineWidth', 3);
>
> How can we extract the x- and y-locations from the contour matrix C in
> matplotlib?
>
-- 
Jonathan D. Slavin
Astrophysicist - High Energy Astrophysics Division
Center for Astrophysics | Harvard & Smithsonian
Office: (617) 496-7981 | Cell: (781) 363-0035
60 Garden Street | MS 83 | Cambridge, MA 02138
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From story645 at gmail.com  Tue Nov 26 16:27:00 2019
From: story645 at gmail.com (Hannah)
Date: Tue, 26 Nov 2019 16:27:00 -0500
Subject: [Matplotlib-users] ANN: contrib_colormaps
Message-ID: <CAOuQ7j38xTNgiO9p5XQAQv0swNvEzGuDhiAkkRn9_f17KWCZ1Q@mail.gmail.com>

Want to make your own custom colormap? And share it with the world?

Check out our new project: https://contrib_colormaps.pyviz.org/
[image: index]

The project provides instructions for making custom colormaps that work
with Matplotlib, colormaps that you can then contribute back to the project
so that your colormaps can be widely available. You can also use the
repository as a model for making your own colormaps:
https://github.com/pyviz/contrib_colormaps
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From nathan.goldbaum at gmail.com  Tue Nov 26 16:46:07 2019
From: nathan.goldbaum at gmail.com (Nathan)
Date: Tue, 26 Nov 2019 14:46:07 -0700
Subject: [Matplotlib-users] ANN: contrib_colormaps
In-Reply-To: <CAOuQ7j38xTNgiO9p5XQAQv0swNvEzGuDhiAkkRn9_f17KWCZ1Q@mail.gmail.com>
References: <CAOuQ7j38xTNgiO9p5XQAQv0swNvEzGuDhiAkkRn9_f17KWCZ1Q@mail.gmail.com>
Message-ID: <CAJXewOkKYz-hieQN-bieGZEk2UFhYhtJCrCnWX7z=Av10rrfvg@mail.gmail.com>

Hi Hannah,

Cool!

However, on firefox at least that site currently complains with the
following SSL error:

Websites prove their identity via certificates. Firefox does not trust this
site because it uses a certificate that is not valid for
contrib_colormaps.pyviz.org. The certificate is only valid for the
following names: www.github.com, *.github.io, *.githubusercontent.com, *.
github.com, github.com, github.io, githubusercontent.com

Error code: SSL_ERROR_BAD_CERT_DOMAIN

-Nathan

On Tue, Nov 26, 2019 at 2:27 PM Hannah <story645 at gmail.com> wrote:

> Want to make your own custom colormap? And share it with the world?
>
> Check out our new project: https://contrib_colormaps.pyviz.org/
> [image: index]
>
> The project provides instructions for making custom colormaps that work
> with Matplotlib, colormaps that you can then contribute back to the project
> so that your colormaps can be widely available. You can also use the
> repository as a model for making your own colormaps:
> https://github.com/pyviz/contrib_colormaps
> _______________________________________________
> Matplotlib-users mailing list
> Matplotlib-users at python.org
> https://mail.python.org/mailman/listinfo/matplotlib-users
>
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From story645 at gmail.com  Tue Nov 26 17:50:44 2019
From: story645 at gmail.com (Hannah)
Date: Tue, 26 Nov 2019 17:50:44 -0500
Subject: [Matplotlib-users] ANN: contrib_colormaps
In-Reply-To: <CAJXewOkKYz-hieQN-bieGZEk2UFhYhtJCrCnWX7z=Av10rrfvg@mail.gmail.com>
References: <CAOuQ7j38xTNgiO9p5XQAQv0swNvEzGuDhiAkkRn9_f17KWCZ1Q@mail.gmail.com>
 <CAJXewOkKYz-hieQN-bieGZEk2UFhYhtJCrCnWX7z=Av10rrfvg@mail.gmail.com>
Message-ID: <CAOuQ7j0njv8HNszekHN1QihRUUu1K=BrkAjC6FWc_qJXyktLPg@mail.gmail.com>

Thanks, wrote up the issue with credit to you (
https://github.com/pyviz/contrib_colormaps/issues/9#issue-529014368) cause
I don't have access to the domain.

On Tue, Nov 26, 2019, 4:46 PM Nathan <nathan.goldbaum at gmail.com> wrote:

> Hi Hannah,
>
> Cool!
>
> However, on firefox at least that site currently complains with the
> following SSL error:
>
> Websites prove their identity via certificates. Firefox does not trust
> this site because it uses a certificate that is not valid for
> contrib_colormaps.pyviz.org. The certificate is only valid for the
> following names: www.github.com, *.github.io, *.githubusercontent.com, *.
> github.com, github.com, github.io, githubusercontent.com
>
> Error code: SSL_ERROR_BAD_CERT_DOMAIN
>
> -Nathan
>
> On Tue, Nov 26, 2019 at 2:27 PM Hannah <story645 at gmail.com> wrote:
>
>> Want to make your own custom colormap? And share it with the world?
>>
>> Check out our new project: https://contrib_colormaps.pyviz.org/
>> [image: index]
>>
>> The project provides instructions for making custom colormaps that work
>> with Matplotlib, colormaps that you can then contribute back to the project
>> so that your colormaps can be widely available. You can also use the
>> repository as a model for making your own colormaps:
>> https://github.com/pyviz/contrib_colormaps
>> _______________________________________________
>> Matplotlib-users mailing list
>> Matplotlib-users at python.org
>> https://mail.python.org/mailman/listinfo/matplotlib-users
>>
>
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