diff --git a/map.py b/map.py
index 383220a..bbb5c24 100644
--- a/map.py
+++ b/map.py
@@ -1,6 +1,6 @@
 import numpy as np
 import matplotlib.pyplot as plt
-from skimage.morphology import remove_small_holes
+# from skimage.morphology import remove_small_holes
 from PIL import Image
 
 
diff --git a/reference_path.py b/reference_path.py
index 83c8fe8..35014db 100644
--- a/reference_path.py
+++ b/reference_path.py
@@ -1,7 +1,7 @@
 import numpy as np
 import math
 from map import Map
-from bresenham import bresenham
+from skimage.draw import line
 import matplotlib.pyplot as plt
 import matplotlib.patches as plt_patches
 from scipy.signal import savgol_filter
@@ -297,8 +297,8 @@ class ReferencePath:
         # Get Bresenham paths to all possible cells
         paths = []
         for t_x, t_y in zip(tn_x, tn_y):
-            path = list(bresenham(wp_x, wp_y, t_x, t_y))
-            paths.append(path)
+            x_list, y_list = line(wp_x, wp_y, t_x, t_y)
+            paths.append(zip(x_list, y_list))
 
         # Compute minimum distance to border cell
         min_width = max_width
@@ -340,7 +340,7 @@ class ReferencePath:
         lb_p = self.map.w2m(wp.border_cells[1][0], wp.border_cells[1][1])
 
         # Compute path from left border cell to right border cell
-        path = list(bresenham(ub_p[0], ub_p[1], lb_p[0], lb_p[1]))
+        x_list, y_list = line(ub_p[0], ub_p[1], lb_p[0], lb_p[1])
 
         # Initialize upper and lower bound of drivable area to
         # upper bound of path
@@ -351,7 +351,7 @@ class ReferencePath:
         ub_ls, lb_ls = ub_p, ub_p
 
         # Iterate over path from left border to right border
-        for x, y in path:
+        for x, y in zip(x_list, y_list):
             # If cell is free, update lower bound
             if self.map.data[y, x] == 1:
                 lb_o = (x, y)
diff --git a/spatial_bicycle_models.py b/spatial_bicycle_models.py
index e307456..74181f8 100644
--- a/spatial_bicycle_models.py
+++ b/spatial_bicycle_models.py
@@ -1,5 +1,13 @@
 import numpy as np
-from abc import ABC, abstractmethod
+from abc import abstractmethod
+try:
+    from abc import ABC
+except:
+    # for Python 2.7
+    from abc import ABCMeta
+    class ABC(object):
+        __metaclass__ = ABCMeta
+        pass
 import matplotlib.pyplot as plt
 import matplotlib.patches as plt_patches
 import math
@@ -26,14 +34,16 @@ class TemporalState:
         self.y = y
         self.psi = psi
 
+        self.members = ['x', 'y', 'psi']
+
     def __iadd__(self, other):
         """
         Overload Sum-Add operator.
         :param other: numpy array to be added to state vector
         """
 
-        for state_id, state in enumerate(vars(self).values()):
-            vars(self)[list(vars(self).keys())[state_id]] += other[state_id]
+        for state_id in range(len(self.members)):
+            vars(self)[self.members[state_id]] += other[state_id]
         return self
 
 
@@ -48,16 +58,21 @@ class SpatialState(ABC):
 
     @abstractmethod
     def __init__(self):
+        self.members = None
         pass
 
     def __getitem__(self, item):
-        return list(vars(self).values())[item]
+        if isinstance(item, int):
+            members = [self.members[item]]
+        else:
+            members = self.members[item]
+        return [vars(self)[key] for key in members]
 
     def __setitem__(self, key, value):
-        vars(self)[list(vars(self).keys())[key]] = value
+        vars(self)[self.members[key]] = value
 
     def __len__(self):
-        return len(vars(self))
+        return len(self.members)
 
     def __iadd__(self, other):
         """
@@ -65,15 +80,15 @@ class SpatialState(ABC):
         :param other: numpy array to be added to state vector
         """
 
-        for state_id, state in enumerate(vars(self).values()):
-            vars(self)[list(vars(self).keys())[state_id]] += other[state_id]
+        for state_id in range(len(self.members)):
+            vars(self)[self.members[state_id]] += other[state_id]
         return self
 
     def list_states(self):
         """
         Return list of names of all states.
         """
-        return list(vars(self).keys())
+        return self.members
 
 
 class SimpleSpatialState(SpatialState):
@@ -91,6 +106,8 @@ class SimpleSpatialState(SpatialState):
         self.e_psi = e_psi
         self.t = t
 
+        self.members = ['e_y', 'e_psi', 't']
+
 
 ####################################
 # Spatial Bicycle Model Base Class #