diff --git a/docs/pvcollada_coordinate_transformation_with_diagram.md b/docs/pvcollada_coordinate_transformation_with_diagram.md
index 6242da2..e7ffccc 100644
--- a/docs/pvcollada_coordinate_transformation_with_diagram.md
+++ b/docs/pvcollada_coordinate_transformation_with_diagram.md
@@ -1,5 +1,5 @@
 
-# PVCollada Coordinate Transformation Guide
+# Guide to Coordinates and Coordinate Transformations
 
 ## ENU Coordinate Frame
 
@@ -14,44 +14,31 @@ latitude, longitude and altitude stored in the COLLADA document.
 
 ## Example Geometry
 
-Cube definition in local coordinates:
+We'll illustrate coordinates and transformations using a cube defined in PVCollada's local coordinates:
 
 - lower corner `(1,1,1)`
 - size `(3,2,1)`
 
-Assume that the topocentric coordinate origin is at the this geolocation:
+![PVCollada cube](pvcollada_cube_diagram.png)
+
+
+## From Local ENU to Geographic Coordinates
+
+Assume that the topocentric coordinate origin is at this geolocation in the WGS84 datum:
 
 - Albuquerque, NM, USA  
 - Latitude `35.0845`  
 - Longitude `-106.651`
 - Altitude `1619`
-- Projection `EPSG:32613`
-
-## Diagram
-
-![PVCollada cube](pvcollada_cube_diagram.png)
-
-The diagram shows the cube in the local coordinate system along with the ENU axes.
+- Projection `EPSG:4326`
 
-## Computed Geographic Coordinates
+EPSG:4326 is the identifier for the WGS-84 geographic coordinate system.
 
-The geocoordinate of the cube are computed using the python library pymap3d.
+The WGS-84 geocoordinates of the cube can be computed using either the pymap3d or pyproj.
 
-|          x |          y |          z |    latitude |     longitude |      altitude |
-|-----------:|-----------:|-----------:|------------:|--------------:|--------------:|
-| 1.00000000 | 1.00000000 | 1.00000000 | 35.08450901 | -106.65098904 | 1620.00000016 |
-| 4.00000000 | 1.00000000 | 1.00000000 | 35.08453605 | -106.65098904 | 1620.00000134 |
-| 1.00000000 | 3.00000000 | 1.00000000 | 35.08450901 | -106.65096711 | 1620.00000078 |
-| 4.00000000 | 3.00000000 | 1.00000000 | 35.08453605 | -106.65096711 | 1620.00000196 |
-| 1.00000000 | 1.00000000 | 2.00000000 | 35.08450901 | -106.65098904 | 1621.00000016 |
-| 4.00000000 | 1.00000000 | 2.00000000 | 35.08453605 | -106.65098904 | 1621.00000134 |
-| 1.00000000 | 3.00000000 | 2.00000000 | 35.08450901 | -106.65096711 | 1621.00000078 |
-| 4.00000000 | 3.00000000 | 2.00000000 | 35.08453605 | -106.65096711 | 1621.00000196 |
- 
-## Python Examples
+### Using pymap3d
 
 ```python
-# Using pymap3d
 
 import pandas as pd
 import pymap3d as pm
@@ -61,7 +48,7 @@ lon0 = -106.651
 alt0 = 1619.0
 
 # Local coordinates of corners of the cube
-coords = pd.DataFrame(
+topocentric_coords = pd.DataFrame(
     columns=['x', 'y', 'z'],
     data=[[1., 1., 1.],
           [4., 1., 1.],
@@ -74,21 +61,35 @@ coords = pd.DataFrame(
     )
 
 # Translate the cube to geocoordinates
+# pymap3d.enu2geodetic uses WGS-84 by default. We'll specify a datum to show how
+# it is done.
+
+datum = pm.Ellipsoid.from_name('wgs84')
 
 lat, lon, alt = pm.enu2geodetic(coords['y'], coords['x'], coords['z'],
-                                lat0, lon0, alt0)
+                                lat0, lon0, alt0, ell=datum)
 
-coords['lat'] = lat
-coords['lon'] = lon
-coords['alt'] = alt
+geodetic_coords = pd.DataFrame({'lat': lat, 'lon': lon, 'alt': alt})
 
-print('Topocentric to Geodetic coordinates')
-print(coords.to_markdown(index=False))
+print('Topocentric to Geodetic coordinates using pymap3d')
+print(geodetic_coords.to_markdown(index=False, floatfmt=".8f"))
 
 ```
+Topocentric to Geodetic coordinates using pymap3d
+|         lat |           lon |           alt |
+|------------:|--------------:|--------------:|
+| 35.08450901 | -106.65098904 | 1620.00000016 |
+| 35.08453605 | -106.65098904 | 1620.00000134 |
+| 35.08450901 | -106.65096711 | 1620.00000078 |
+| 35.08453605 | -106.65096711 | 1620.00000196 |
+| 35.08450901 | -106.65098904 | 1621.00000016 |
+| 35.08453605 | -106.65098904 | 1621.00000134 |
+| 35.08450901 | -106.65096711 | 1621.00000078 |
+| 35.08453605 | -106.65096711 | 1621.00000196 |
+
+### Using pyproj
 
 ```python
-# Using pyproj
 
 import pandas as pd
 import pyproj
@@ -132,11 +133,57 @@ coords = pd.DataFrame(
 lon, lat, alt = transformer.transform(
     coords['x'], coords['y'], coords['z'])
 
-coords['latitude'] = lat
-coords['longitude'] = lon
-coords['altitude'] = alt
+geodetic_coords = pd.DataFrame({'lat': lat, 'lon': lon, 'alt': alt})
+
+print('Topocentric to Geodetic coordinates using pymap3d')
+print(geodetic_coords.to_markdown(index=False, floatfmt=".8f"))
+
+```
+
+## From Geographic or Projected Coordinates to PVCollada ENU
+
+We'll show how we can reverse the above transformation, from WGS-84 geographic coordinates to PVCollada's ENU coordinates,
+using either pymap3d or pyproj.
+
+### Using pymap3d
 
-print('Topocentric to Geodetic coordinates')
+```python
+
+import numpy as np
+import pandas as pd
+import pymap3d as pm
+
+
+geocoords = pd.DataFrame(
+    columns=['lat', 'lon', 'alt'],
+    data = np.array(
+	    [[35.08450901, -106.65098904, 1620.00000016],
+         [35.08453605, -106.65098904, 1620.00000134],
+         [35.08450901, -106.65096711, 1620.00000078],
+         [35.08453605, -106.65096711, 1620.00000196],
+         [35.08450901, -106.65098904, 1621.00000016],
+         [35.08453605, -106.65098904, 1621.00000134],
+         [35.08450901, -106.65096711, 1621.00000078],
+         [35.08453605, -106.65096711, 1621.00000196]]
+        )
+    )
+
+# origin of ENU coordinates
+lat0 = 35.0845
+lon0 = -106.651
+alt0 = 1619.0
+datum = pm.Ellipsoid.from_name('wgs84')
+
+x, y, z = pm.geodetic2enu(
+    geocoords['lat'], geocoords['lon'], geocoords['alt'], 
+    lat0, lon0, alt0, ell=datum
+	)
+
+# put x, y, z into a DataFrame for convenient printing
+enucoords = pd.DataFrame({'x': x, 'y': y, 'z': z})
+
+print('Geodetic to Topocentric coordinates using pymap3d')
 print(coords.to_markdown(index=False, floatfmt=".8f"))
 
 ```
+