ENH: Added details on use of TubeSpatialObjects.

Author: aylward

SoftwareGuide/Latex/Architecture/SpatialObjects.tex

@@ -148,8 +148,11 @@ \subsection{SurfaceSpatialObject}
 \subsection{TubeSpatialObject}
 
 \doxygen{TubeSpatialObject} is a class for the representation
-of tubular structures using SpatialObjects.
- The class \doxygen{DTITubeSpatialObject} is derive from this base class
+of tubular structures using SpatialObjects.  In particular, it is intended
+to be used to represent vascular networks extracted from 2D and 3D images.
+It can also be used to represent airways, nerves, bile ducts, and more.
+
+ The class \doxygen{DTITubeSpatialObject} is derived from this class
 and adds constructs for representing fiber tracts from diffusion tensor images.
 
 \label{sec:TubeSpatialObject}