DOC: Add an example for 2D images in 3D plots

galleries/examples/mplot3d/imshow3d.py

@@ -0,0 +1,88 @@
+"""
+===============
+2D images in 3D
+===============
+
+This example demonstrates how to plot 2D color coded images (similar to
+`.Axes.imshow`) as a plane in 3D.
+
+Matplotlib does not have a native function for this. Below we build one by relying
+on `.Axes3D.plot_surface`. For simplicity, there are some differences to
+`.Axes.imshow`: This function does not set the aspect of the Axes, hence pixels are
+not necessarily square. Also, pixel edges are on integer values rather than pixel
+centers. Furthermore, many optional parameters of `.Axes.imshow` are not implemented.
+
+Multiple calls of ``imshow3d`` use independent norms and thus different color scales
+by default. If you want to have a single common color scale, you need to construct
+a suitable norm beforehand and pass it to all ``imshow3d`` calls.
+
+A fundamental limitation of the 3D plotting engine is that intersecting objects cannot
+be drawn correctly. One object will always be drawn after the other. Therefore,
+multiple image planes can well be used in the background as shown in this example.
+But this approach is not suitable if the planes intersect.
+"""
+
+import matplotlib.pyplot as plt
+import numpy as np
+
+from matplotlib.colors import Normalize
+
+
+def imshow3d(ax, array, value_direction='z', pos=0, norm=None, cmap=None):
+    """
+    Display a 2D array as a  color-coded 2D image embedded in 3d.
+
+    The image will be in a plane perpendicular to the coordinate axis *value_direction*.
+
+    Parameters
+    ----------
+    ax : Axes3D
+        The 3D Axes to plot into.
+    array : 2D numpy array
+        The image values.
+    value_direction : {'x', 'y', 'z'}
+        The axis normal to the image plane.
+    pos : float
+        The numeric value on the *value_direction* axis at which the image plane is
+        located.
+    norm : `~matplotlib.colors.Normalize`, default: Normalize
+        The normalization method used to scale scalar data. See `imshow()`.
+    cmap : str or `~matplotlib.colors.Colormap`, default: :rc:`image.cmap`
+        The Colormap instance or registered colormap name used to map scalar data
+        to colors.
+    """
+    if norm is None:
+        norm = Normalize()
+    colors = plt.get_cmap(cmap)(norm(array))
+
+    if value_direction == 'x':
+        nz, ny = array.shape
+        zi, yi = np.mgrid[0:nz + 1, 0:ny + 1]
+        xi = np.full_like(yi, pos)
+    elif value_direction == 'y':
+        nx, nz = array.shape
+        xi, zi = np.mgrid[0:nx + 1, 0:nz + 1]
+        yi = np.full_like(zi, pos)
+    elif value_direction == 'z':
+        ny, nx = array.shape
+        yi, xi = np.mgrid[0:ny + 1, 0:nx + 1]
+        zi = np.full_like(xi, pos)
+    else:
+        raise ValueError(f"Invalid value_direction: {value_direction!r}")
+    ax.plot_surface(xi, yi, zi, rstride=1, cstride=1, facecolors=colors, shade=False)
+
+
+fig = plt.figure()
+ax = fig.add_subplot(projection='3d')
+ax.set(xlabel="x", ylabel="y", zlabel="z")
+
+nx, ny, nz = 8, 10, 5
+data_xy = np.arange(ny * nx).reshape(ny, nx) + 15 * np.random.random((ny, nx))
+data_yz = np.arange(nz * ny).reshape(nz, ny) + 10 * np.random.random((nz, ny))
+data_zx = np.arange(nx * nz).reshape(nx, nz) + 8 * np.random.random((nx, nz))
+
+imshow3d(ax, data_xy)
+imshow3d(ax, data_yz, value_direction='x', cmap='magma')
+imshow3d(ax, data_zx, value_direction='y', pos=ny, cmap='plasma')
+
+plt.show()