Improvements and docs for QuadMesh

examples/reference/elements/bokeh/QuadMesh.ipynb

@@ -104,6 +104,40 @@
    "source": [
     "Now when you hover over this visualization, you can see the sample value as well as an outline of the selected bin."
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Irregular meshes\n",
+    "\n",
+    "In addition to axis aligned meshes like those we worked with above, a ``QuadMesh`` may also be used to represent irregular meshes. In this example we will create an irregular mesh consisting of 2D X, Y and Z arrays defining the position and value of each simplex in the mesh:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "n=20\n",
+    "coords = np.linspace(-1.5,1.5,n)\n",
+    "X,Y = np.meshgrid(coords, coords);\n",
+    "Qx = np.cos(Y) - np.cos(X)\n",
+    "Qz = np.sin(Y) + np.sin(X)\n",
+    "Z = np.sqrt(X**2 + Y**2)\n",
+    "\n",
+    "print(Qx.shape, Qz.shape, Z.shape)\n",
+    "qmesh = hv.QuadMesh((Qx, Qz, Z))\n",
+    "qmesh"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Unlike regular meshes an irregularly sampled mesh cannot be selected or grouped by value."
+   ]
   }
  ],
  "metadata": {

examples/reference/elements/matplotlib/QuadMesh.ipynb

@@ -86,6 +86,40 @@
    "source": [
     "To use an interactive hover tool to inspect the sample values, you can use ``QuadMesh`` with the hover tool in the [Bokeh backend](../bokeh/QuadMesh.ipynb)"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Irregular meshes\n",
+    "\n",
+    "In addition to axis aligned meshes like those we worked with above, a ``QuadMesh`` may also be used to represent irregular meshes. In this example we will create an irregular mesh consisting of 2D X, Y and Z arrays defining the position and value of each simplex in the mesh:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "n=20\n",
+    "coords = np.linspace(-1.5,1.5,n)\n",
+    "X,Y = np.meshgrid(coords, coords);\n",
+    "Qx = np.cos(Y) - np.cos(X)\n",
+    "Qz = np.sin(Y) + np.sin(X)\n",
+    "Z = np.sqrt(X**2 + Y**2)\n",
+    "\n",
+    "print(Qx.shape, Qz.shape, Z.shape)\n",
+    "qmesh = hv.QuadMesh((Qx, Qz, Z))\n",
+    "qmesh + qmesh.opts(style=dict(shading='gouraud'))"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Unlike regular meshes an irregularly sampled mesh cannot be selected or grouped by value."
+   ]
   }
  ],
  "metadata": {

holoviews/core/data/grid.py

@@ -174,7 +174,7 @@ def coords(cls, dataset, dim, ordered=False, expanded=False, edges=False):
                 data = dataset.data[dim.name]
             else:
                 data = util.expand_grid_coords(dataset, dim)
-            if edges:
+            if edges and data.shape == dataset.data[dataset.vdims[0].name].shape:
                 data = cls._infer_interval_breaks(data, axis=1)
                 data = cls._infer_interval_breaks(data, axis=0)
             return data
@@ -186,7 +186,7 @@ def coords(cls, dataset, dim, ordered=False, expanded=False, edges=False):
         isedges = (dim in dataset.kdims and len(shape) == dataset.ndims
                    and len(data) == (shape[dataset.ndims-idx-1]+1))
         if edges and not isedges:
-            data = util.compute_edges(data)
+            data = cls._infer_interval_breaks(data)
         elif not edges and isedges:
             data = np.convolve(data, [0.5, 0.5], 'valid')
         return data
@@ -273,10 +273,12 @@ def ndloc(cls, dataset, indices):
                 selected[kd.name] = coords
                 all_scalar = False
         for d in dataset.dimensions():
-            arr = dataset.dimension_values(vd, flat=False)
+            if d in dataset.kdims and cls.irregular(dataset, d):
+                continue
+            arr = dataset.dimension_values(d, flat=False)
             if all_scalar and len(dataset.vdims) == 1:
                 return arr[tuple(ind[0] for ind in adjusted_inds)]
-            selected[vd.name] = arr[tuple(adjusted_inds)]
+            selected[d.name] = arr[tuple(adjusted_inds)]
         return tuple(selected[d.name] for d in dataset.dimensions())
 
 

holoviews/core/data/image.py

@@ -58,6 +58,10 @@ def init(cls, eltype, data, kdims, vdims):
 
         return data, {'kdims':kdims, 'vdims':vdims}, kwargs
 
+    @classmethod
+    def irregular(cls, dataset, dim):
+        "ImageInterface does not support irregular data"
+        return False
 
     @classmethod
     def shape(cls, dataset, gridded=False):

holoviews/plotting/mpl/raster.py

@@ -234,38 +234,39 @@ def get_data(self, element, ranges, style):
         zdata = element.dimension_values(2, flat=False)
         data = np.ma.array(zdata, mask=np.logical_not(np.isfinite(zdata)))
         expanded = element.interface.irregular(element, element.kdims[0])
-        coords = [element.interface.coords(element, d, expanded=expanded, edges=True)
+        edges = style.get('shading') != 'gouraud'
+        coords = [element.interface.coords(element, d, expanded=expanded, edges=edges)
                   for d in element.kdims]
         if self.invert_axes:
             coords = coords[::-1]
             data = data.T
         cmesh_data = coords + [data]
-        style['locs'] = np.concatenate(coords)
+        if expanded:
+            style['locs'] = np.concatenate(coords)
         vdim = element.vdims[0]
         self._norm_kwargs(element, ranges, style, vdim)
         return tuple(cmesh_data), style, {}
 
 
     def init_artists(self, ax, plot_args, plot_kwargs):
-        locs = plot_kwargs.pop('locs')
+        locs = plot_kwargs.pop('locs', None)
         artist = ax.pcolormesh(*plot_args, **plot_kwargs)
         return {'artist': artist, 'locs': locs}
 
 
     def update_handles(self, key, axis, element, ranges, style):
         cmesh = self.handles['artist']
-        locs = np.concatenate(element.data[:2])
-
-        if (locs != self.handles['locs']).any():
-            return super(QuadMeshPlot, self).update_handles(key, axis, element,
-                                                            ranges, style)
-        else:
-            data, style, axis_kwargs = self.get_data(element, ranges, style)
+        data, style, axis_kwargs = self.get_data(element, ranges, style)
+        locs = style.get('locs')
+        old_locs = self.handles.get('locs')
+        if None in (locs, old_locs) or (locs == old_locs).all():
             cmesh.set_array(data[-1])
             cmesh.set_clim((style['vmin'], style['vmax']))
             if 'norm' in style:
                 cmesh.norm = style['norm']
             return axis_kwargs
+        return super(QuadMeshPlot, self).update_handles(key, axis, element,
+                                                        ranges, style)
 
 
 class RasterGridPlot(GridPlot, OverlayPlot):