Mailman 3 November 2019 - Matplotlib-users

ANN: contrib_colormaps
by Hannah Nov. 26, 2019

Nov. 26, 2019

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

2 2

Re: [Matplotlib-users] Extract the x- and y-locations from the contour matrix C
by Slavin, Jonathan Nov. 6, 2019

Nov. 6, 2019

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(a)googlemail.com> > To: matplotlib-users(a)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(a)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

1 0

Extract the x- and y-locations from the contour matrix C
by Nils Wagner Nov. 6, 2019

Nov. 6, 2019

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?

1 0

When was axes kwarg rmoved?
by Vicki Brown Nov. 1, 2019

Nov. 1, 2019

I'm hoping someone can tell me (point me to the ChanegLog for) when he axes kwarg was removed from matplotlib.pyplot.clabel, matplotlib.pyplot.contou, and matplotlib.pyplot.contourf. My search has turned up nothing. I have code in an exercise for a class that called: plt.contourf(xx, yy, Z, cmap=ccolor, alpha=.2, axes=ax) cs2 = plt.contour(xx, yy, Z, cmap=ccolor, alpha=.6, axes=ax) plt.clabel(cs2, fmt = '%2.1f', colors = 'k', fontsize=14, axes=ax) when run, this raised errors. I've changed it to ax.contourf(xx, yy, Z, cmap=ccolor, alpha=.2) cs2 = ax.contour(xx, yy, Z, cmap=ccolor, alpha=.6) ax.clabel(cs2, fmt = '%2.1f', colors = 'k', fontsize=14) and the errors are gone. However, a confirming reference would be helpful. -- Vicki Vicki Brown cfcl.com/vlb

3 6