Cleaned up datashader class hierarchy

holoviews/operation/datashader.py

@@ -164,9 +164,10 @@ class aggregate(ResamplingOperation):
     """
     aggregate implements 2D binning for any valid HoloViews Element
     type using datashader. I.e., this operation turns a HoloViews
-    Element or overlay of Elements into an hImage or an overlay of
-    .Images by rasterizing it, which provides a fixed-sized
-    representation independent of the original dataset size.
+    Element or overlay of Elements into an Image or an overlay of
+    Images by rasterizing it. This allows quickly aggregating large
+    datasets computing a fixed-sized representation independent
+    of the original dataset size.
 
     By default it will simply count the number of values in each bin
     but other aggregators can be supplied implementing mean, max, min
@@ -486,7 +487,7 @@ def _process(self, element, key=None):
         return element.clone(regridded, bounds=bbox, datatype=['xarray'])
 
 
-class trimesh_rasterize(aggregate):
+class trimesh_rasterize(ResamplingOperation):
     """
     Rasterize the TriMesh element using the supplied aggregator. If
     the TriMesh nodes or edges define a value dimension will plot
@@ -527,11 +528,13 @@ def _process(self, element, key=None):
         return Image(agg, **params)
 
 
-class rasterize(trimesh_rasterize):
+
+class rasterize(ResamplingOperation):
     """
     Rasterize is a high-level operation which will rasterize any
-    Element or combination of Elements supplied as an (Nd)Overlay
-    by aggregating with the supplied aggregation function.
+    Element or combination of Elements supplied as an (Nd)Overlay by
+    aggregating with the supplied aggregation it with the declared
+    aggregator and interpolation methods.
 
     By default it will simply count the number of values in each bin
     but other aggregators can be supplied implementing mean, max, min
@@ -552,6 +555,10 @@ class rasterize(trimesh_rasterize):
     aggregator = param.ClassSelector(class_=ds.reductions.Reduction,
                                      default=None)
 
+    interpolation = param.ObjectSelector(default='bilinear',
+                                         objects=['bilinear', None], doc="""
+        The interpolation method to apply during rasterization.""")
+
     def _process(self, element, key=None):
         # Get input Images to avoid multiple rasterization
         imgs = element.traverse(lambda x: x, [Image])