diff --git a/galleries/examples/mplot3d/intersecting_planes.py b/galleries/examples/mplot3d/intersecting_planes.py new file mode 100644 index 000000000000..b8aa08fd7e18 --- /dev/null +++ b/galleries/examples/mplot3d/intersecting_planes.py @@ -0,0 +1,89 @@ +""" +=================== +Intersecting planes +=================== + +This examples demonstrates drawing intersecting planes in 3D. It is a generalization +of :doc:`/gallery/mplot3d/imshow3d`. + +Drawing intersecting planes in `.mplot3d` is complicated, because `.mplot3d` is not a +real 3D renderer, but only projects the Artists into 3D and draws them in the right +order. This does not work correctly if Artists overlap each other mutually. In this +example, we lift the problem of mutual overlap by segmenting the planes at their +intersections, making four parts out of each plane. + +This examples only works correctly for planes that cut each other in haves. This +limitation is intentional to keep the code more readable. Cutting at arbitrary +positions would of course be possible but makes the code even more complex. +Thus, this example is more a demonstration of the concept how to work around +limitations of the 3D visualization, it's not a refined solution for drawing +arbitrary intersecting planes, which you can copy-and-paste as is. +""" +import matplotlib.pyplot as plt +import numpy as np + + +def plot_quadrants(ax, array, fixed_coord, cmap): + """For a given 3d *array* plot a plane with *fixed_coord*, using four quadrants.""" + nx, ny, nz = array.shape + index = { + 'x': (nx // 2, slice(None), slice(None)), + 'y': (slice(None), ny // 2, slice(None)), + 'z': (slice(None), slice(None), nz // 2), + }[fixed_coord] + plane_data = array[index] + + n0, n1 = plane_data.shape + quadrants = [ + plane_data[:n0 // 2, :n1 // 2], + plane_data[:n0 // 2, n1 // 2:], + plane_data[n0 // 2:, :n1 // 2], + plane_data[n0 // 2:, n1 // 2:] + ] + + min_val = array.min() + max_val = array.max() + + cmap = plt.get_cmap(cmap) + + for i, quadrant in enumerate(quadrants): + facecolors = cmap((quadrant - min_val) / (max_val - min_val)) + if fixed_coord == 'x': + Y, Z = np.mgrid[0:ny // 2, 0:nz // 2] + X = nx // 2 * np.ones_like(Y) + Y_offset = (i // 2) * ny // 2 + Z_offset = (i % 2) * nz // 2 + ax.plot_surface(X, Y + Y_offset, Z + Z_offset, rstride=1, cstride=1, + facecolors=facecolors, shade=False) + elif fixed_coord == 'y': + X, Z = np.mgrid[0:nx // 2, 0:nz // 2] + Y = ny // 2 * np.ones_like(X) + X_offset = (i // 2) * nx // 2 + Z_offset = (i % 2) * nz // 2 + ax.plot_surface(X + X_offset, Y, Z + Z_offset, rstride=1, cstride=1, + facecolors=facecolors, shade=False) + elif fixed_coord == 'z': + X, Y = np.mgrid[0:nx // 2, 0:ny // 2] + Z = nz // 2 * np.ones_like(X) + X_offset = (i // 2) * nx // 2 + Y_offset = (i % 2) * ny // 2 + ax.plot_surface(X + X_offset, Y + Y_offset, Z, rstride=1, cstride=1, + facecolors=facecolors, shade=False) + + +def figure_3D_array_slices(array, cmap=None): + """Plot a 3d array using three intersecting centered planes.""" + fig = plt.figure() + ax = fig.add_subplot(projection='3d') + ax.set_box_aspect(array.shape) + plot_quadrants(ax, array, 'x', cmap=cmap) + plot_quadrants(ax, array, 'y', cmap=cmap) + plot_quadrants(ax, array, 'z', cmap=cmap) + return fig, ax + + +nx, ny, nz = 70, 100, 50 +r_square = (np.mgrid[-1:1:1j * nx, -1:1:1j * ny, -1:1:1j * nz] ** 2).sum(0) + +figure_3D_array_slices(r_square, cmap='viridis_r') +plt.show()