diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 23828b49..82d9e733 100755
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -28,16 +28,24 @@ The readme contains some tips on running tests.
 
 For dev you will need to install the requirements-dev.txt file.
 
-clone the repo an cd into it.
+Clone the repo an cd into it.
 
-setup a virtual environment
+Setup a virtual environment:
 
+**BASH**
 ```bash
 python3 -m venv venv
 . venv/bin/activate
 pip install -r requirements-dev.txt
 ```
 
+**PowerShell**
+```powershell
+python3 -m venv winvenv
+. .\winvenv\Scripts\activate
+pip install -r requirements-dev.txt
+```
+
 and you should be good to go.
 
 The Makefile can be used to run all tests.
diff --git a/domonic/d3/polygon.py b/domonic/d3/polygon.py
index 01613ec6..2db075f8 100644
--- a/domonic/d3/polygon.py
+++ b/domonic/d3/polygon.py
@@ -44,7 +44,6 @@ def polygonCentroid(polygon):
     k *= 3
     return [x / k, y / k]
 
-
 def cross(a, b, c):
     """[Returns the 2D cross product of AB and AC vectors, i.e., the z-component of
         the 3D cross product in a quadrant I Cartesian coordinate system (+x is
@@ -61,73 +60,34 @@ def cross(a, b, c):
     """
     return (b[0] - a[0]) * (c[1] - a[1]) - (b[1] - a[1]) * (c[0] - a[0])
 
-
-def lexicographicOrder(a, b, *args):
-    return a[0] - b[0] or a[1] - b[1]
-
-
-def computeUpperHullIndexes(points):
-    """[Computes the upper convex hull per the monotone chain algorithm.
-        Assumes points.length >= 3, is sorted by x, unique in y.
-        Returns an array of indices into points in left-to-right order.]
-
-    Args:
-        points ([type]): [description]
-    """
-    n = len(points)
-    indexes = [0, 1]
-    size = 2
-    for i in range(2, n):
-        while (size > 1 and cross(points[indexes[size - 2]], points[indexes[size - 1]], points[i]) <= 0):
-            size -= 1
-        size += 1
-        indexes[size] = i
-
-    return Array(indexes).slice(0, size)  # remove popped points
-
-
 def polygonHull(points):
 
     n = len(points)
     if n < 3:
         return None
 
-    sortedPoints = []
-    flippedPoints = []
-
-    print(points)
-
-    for i in range(0, n):
-        print( points[i][0], points[i][1], i)
-        sortedPoints.append([points[i][0], points[i][1], i])
-
-    print(sortedPoints)
-
-    sortedPoints = Array(sortedPoints).sort(lexicographicOrder)
-
-    for i in range(0, n):
-        flippedPoints[i] = [sortedPoints[i][0], -sortedPoints[i][1]]
-
-    upperIndexes = computeUpperHullIndexes(sortedPoints)
-    lowerIndexes = computeUpperHullIndexes(flippedPoints)
-
-    # Construct the hull polygon, removing possible duplicate endpoints.
-    skipLeft = lowerIndexes[0] == upperIndexes[0]
-    skipRight = lowerIndexes[len(lowerIndexes) - 1] == upperIndexes[len(upperIndexes) - 1]
-    hull = []
-
-    # Add upper hull in right-to-l order.
-    # Then add lower hull in left-to-right order.
-    i = len(upperIndexes)
-    while i >= 0:
-        hull.append(points[sortedPoints[upperIndexes[i]][2]])
-        i -= 1
-
-    i = skipLeft
-    while i < len(lowerIndexes) - skipRight:
-        hull.append(points[sortedPoints[lowerIndexes[i]][2]])
-        i += 1
-
+    # Convert list to tuples and remove duplicates
+    points = [t for t in (set(tuple(i) for i in points))]
+
+    # Sort lexicographically 
+    points = sorted(points)
+
+    # Build hulls according to Andrew's monotone chain algorithm
+    lowerHull = []
+    for p in points:
+        while len(lowerHull) >= 2 and cross(lowerHull[-2], lowerHull[-1], p) <=0 :
+            lowerHull.pop()
+        lowerHull.append(p)
+
+    upperHull = []
+    for p in reversed(points):
+        while len(upperHull) >= 2 and cross(upperHull[-2], upperHull[-1], p) <= 0:
+            upperHull.pop()
+        upperHull.append(p)
+    
+    # Build polygon hull from upper/lower hulls and return to list form
+    hull = sorted([list(i) for i in lowerHull[:-1] + upperHull[:-1]])
+    
     return hull
 
 
@@ -171,4 +131,4 @@ def polygonLength(polygon):
         ya -= yb
         perimeter += Math.hypot(xa, ya)
         i += 1
-    return perimeter
+    return perimeter
\ No newline at end of file
diff --git a/tests/test_d3.py b/tests/test_d3.py
index ba972ff8..f9793b62 100644
--- a/tests/test_d3.py
+++ b/tests/test_d3.py
@@ -1541,13 +1541,29 @@ def test_polygonArea(self):
         self.assertEqual(polygonArea(square), 16)
         self.assertEqual(polygonArea(triangle), 12)
         
-    # def test_polygonCentroid():
-    # def test_cross():
-    # def test_lexicographicOrder():
-    # def test_polygonHull():
+    def test_polygonCentroid(self): 
+        irreg = [[-4,0],[8,12],[4,8],[-4,-4],[0,0]] # centroid: [0, 4]
+        square = [[0,4],[4,4],[4,0],[0,0]]          # centroid: [2, 2]
+        triangle = [[-4,0],[0,4],[4,2]]             # centroid: [0, 2]
+
+        self.assertEqual(polygonCentroid(irreg), [0, 4])
+        self.assertEqual(polygonCentroid(square), [2, 2])
+        self.assertEqual(polygonCentroid(triangle), [0, 2])
+
+    def test_polygonHull(self):
+        points_0 = [[0,6],[12,8],[23,-5],[-5,-3],[5,11],[12,4],[7,7],[6,1]]
+        points_1 = [[-4,0],[8,12],[4,8],[-4,-4],[0,0],[-6,12],[23,2],[19,-8],[-7,-6]]
+
+        hull_0 = [[-5,-3],[0,6],[5,11],[12,8],[23,-5]]
+        hull_1 = [[-7,-6],[-6,12],[8,12],[19,-8],[23,2]]
+        
+        self.assertEqual(polygonHull(points_0), hull_0)
+        self.assertEqual(polygonHull(points_1), hull_1)
+
+
     # def test_polygonContains():
     # def test_polygonLength():
         
 
 if __name__ == '__main__':
-    unittest.main()
+    unittest.main()
\ No newline at end of file