set default iteration count for #280

automatically update step, spread and PE count based on length changes
set default ATL03 version to 006

clients/python/sliderule/ipysliderule.py

@@ -104,8 +104,8 @@ def __init__(self, **kwargs):
 
         # dropdown menu for setting data release
         self.release = ipywidgets.Dropdown(
-            options=['003', '004', '005'],
-            value='005',
+            options=['003', '004', '005', '006'],
+            value='006',
             description='Release:',
             description_tooltip="Release: ICESat-2 data release",
             disabled=False,
@@ -351,7 +351,7 @@ def __init__(self, **kwargs):
         # slider for setting maximum number of iterations
         # (not including initial least-squares-fit selection)
         self.iteration = ipywidgets.IntSlider(
-            value=1,
+            value=6,
             min=0,
             max=20,
             step=1,
@@ -432,6 +432,9 @@ def __init__(self, **kwargs):
             style=self.style,
         )
 
+        # watch widgets for changes
+        self.length.observe(self.set_default_values_from_length)
+
         # dropdown menu for setting map projection
         # Global: Web Mercator (EPSG:3857)
         # North: Alaska Polar Stereographic (EPSG:5936)
@@ -732,6 +735,14 @@ def time_end(self):
         """
         return self.end_date.value.isoformat()
 
+    # function for setting default values when segment length changes
+    def set_default_values_from_length(self, sender):
+        """function for setting default values when segment length changes
+        """
+        self.step.value = int(self.length.value//2)
+        self.spread.value = self.length.value/2.0
+        self.count.value = np.maximum(5, self.length.value//4)
+
     # function for setting available map layers
     def set_layers(self, sender):
         """function for updating available map layers