doctoring edits, and allow for data to be URL

Author: andrewgiessel

folium/folium.py

@@ -954,26 +954,27 @@ def image_overlay(self, data, opacity=0.25, min_lat=-90.0, max_lat=90.0,
         way to overlay geospatial data on top of a map.  If your data is high res, consider
         implementing a WMS server and adding a WMS layer.
 
-        This function works by using the imageio library to generate a PNG file in 
+        This function works by generating a PNG file from a numpy array.  If you do not
+        specifiy a filename, it will embed the image inline.  Otherwise, it saves the file in the
         current directory, and then adds it as an image overlay layer in leaflet.js.
         By default, the image is placed and stretched using bounds that cover the 
         entire globe.
 
         Parameters
         ----------
-        data: numpy array, required.  
-            Must be a valid format for imageio.imwriter(), i.e., NxM (mono), 
-            NxMx3 (rgb), or NxMx4 (rgba)
+        data: numpy array OR url string, required.  
+            if numpy array, must be a image format, i.e., NxM (mono), NxMx3 (rgb), or NxMx4 (rgba)
+            if url, must be a valid url to a image (local or external)
         opacity: float, default 0.25
-            image layer opacity in range 0 (completely transparent) to 1 (opaque)
+            Image layer opacity in range 0 (completely transparent) to 1 (opaque)
         min_lat: float, default -90.0
         max_lat: float, default  90.0
         min_lon: float, default -180.0
         max_lon: float, default  180.0
         image_name: string, default None
-            the name of the layer object in leaflet.js
+            The name of the layer object in leaflet.js
         filename: string, default None
-            optional file name of output.png for image overlay.  If None, we use a 
+            Optional file name of output.png for image overlay.  If None, we use a 
             inline PNG.
 
         Output
@@ -999,20 +1000,19 @@ def image_overlay(self, data, opacity=0.25, min_lat=-90.0, max_lat=90.0,
         
         """
 
-        # todo add URL
         if isinstance(data, str):
-            raise NotImplementedError
-
-        try:
-            png_str = utilities.write_png(data)
-        except Exception as e:
-            raise e
-
-        if filename is not None:
-            with open(filename, 'wb') as fd:
-                fd.write(png_str)
+            filename = data
         else:
-            filename = "data:image/png;base64,"+base64.b64encode(png_str).decode('utf-8')
+            try:
+                png_str = utilities.write_png(data)
+            except Exception as e:
+                raise e
+
+            if filename is not None:
+                with open(filename, 'wb') as fd:
+                    fd.write(png_str)
+            else:
+                filename = "data:image/png;base64,"+base64.b64encode(png_str).decode('utf-8')
 
         if image_name not in self.added_layers:
             if image_name is None:
@@ -1031,7 +1031,6 @@ def image_overlay(self, data, opacity=0.25, min_lat=-90.0, max_lat=90.0,
                                        'image_opacity': image_opacity})
 
             self.template_vars['image_layers'].append(image)
-#            self.added_layers.append({image_name: image_url})
             self.added_layers.append(image_name)
 
     def _build_map(self, html_templ=None, templ_type='string'):