matplotlib
diff --git a/‎lib/mpl_toolkits/mplot3d/axis3d.py
+27-4 b/‎lib/mpl_toolkits/mplot3d/axis3d.py
+27-4
diff --git a/‎lib/mpl_toolkits/tests/baseline_images/test_mplot3d/axes3d_primary_views.png
7.43 KB b/‎lib/mpl_toolkits/tests/baseline_images/test_mplot3d/axes3d_primary_views.png
7.43 KB
diff --git a/‎lib/mpl_toolkits/tests/baseline_images/test_mplot3d/axes3d_rotated.png
244 Bytes b/‎lib/mpl_toolkits/tests/baseline_images/test_mplot3d/axes3d_rotated.png
244 Bytes
diff --git a/‎lib/mpl_toolkits/tests/test_mplot3d.py
+20-3 b/‎lib/mpl_toolkits/tests/test_mplot3d.py
+20-3
@@ -231,11 +231,34 @@ def _get_coord_info(self, renderer):
         bounds_proj = self.axes.tunit_cube(bounds, self.axes.M)
 
         # Determine which one of the parallel planes are higher up:
-        highs = np.zeros(3, dtype=bool)
+        means_z0 = np.zeros(3)
+        means_z1 = np.zeros(3)
         for i in range(3):
-            mean_z0 = np.mean(bounds_proj[self._PLANES[2 * i], 2])
-            mean_z1 = np.mean(bounds_proj[self._PLANES[2 * i + 1], 2])
-            highs[i] = mean_z0 < mean_z1
+            means_z0[i] = np.mean(bounds_proj[self._PLANES[2 * i], 2])
+            means_z1[i] = np.mean(bounds_proj[self._PLANES[2 * i + 1], 2])
+        highs = means_z0 < means_z1
+
+        # Special handling for edge-on views
+        equals = np.abs(means_z0 - means_z1) <= np.finfo(float).eps
+        if np.sum(equals) == 2:
+            vertical = np.where(np.invert(equals))[0][0]
+            if vertical == 2:
+                if highs[2]:  # looking at -XY plane
+                    highs[0] = False
+                    highs[1] = True
+                else:  # looking at +XY plane
+                    highs[0] = True
+                    highs[1] = True
+            elif vertical == 1:
+                if highs[1]:  # looking at +XZ plane
+                    highs[0] = True
+                else:  # looking at -XZ plane
+                    pass
+            elif vertical == 0:
+                if highs[0]:  # looking at -YZ plane
+                    highs[1] = True
+                else:  # looking at +YZ plane
+                    pass
 
         return mins, maxs, centers, deltas, bounds_proj, highs
 
 
@@ -60,6 +60,23 @@ def test_axes3d_repr():
         "title={'center': 'title'}, xlabel='x', ylabel='y', zlabel='z'>")
 
 
+@mpl3d_image_comparison(['axes3d_primary_views.png'])
+def test_axes3d_primary_views():
+    # (view, (elev, azim, roll))
+    views = [(90, -90, 0),  # XY
+             (0, -90, 0),   # XZ
+             (0, 0, 0),     # YZ
+             (-90, 90, 0),  # -XY
+             (0, 90, 0),    # -XZ
+             (0, 180, 0)]   # -YZ
+    # When viewing primary planes, draw the two other axes on left and bottom
+    fig, axs = plt.subplots(2, 3, subplot_kw={'projection': '3d'})
+    for i, ax in enumerate([ax for ax_row in axs for ax in ax_row]):
+        ax.set_proj_type('ortho')
+        ax.view_init(elev=views[i][0], azim=views[i][1], roll=views[i][2])
+    plt.tight_layout()
+
+
 @mpl3d_image_comparison(['bar3d.png'])
 def test_bar3d():
     fig = plt.figure()
@@ -1839,9 +1856,9 @@ def test_scatter_spiral():
                 [0.0, 0.0, -1.142857, 10.571429],
             ],
             [
-                ([0.06329114, -0.06329114], [-0.04746835, -0.04746835]),
-                ([-0.06329114, -0.06329114], [0.04746835, -0.04746835]),
-                ([0.05617978, 0.06329114], [-0.04213483, -0.04746835]),
+                ([-0.06329114, 0.06329114], [0.04746835, 0.04746835]),
+                ([0.06329114, 0.06329114], [-0.04746835, 0.04746835]),
+                ([-0.05617978, -0.06329114], [0.04213483, 0.04746835]),
             ],
             [2, 2, 0],
         ),