  <li>Example files:
          <ul>
            <li><a href="gtl_point_usage.htm">point_usage.cpp</a> Using
the library provided point data type and functions</li>
            <li><a href="gtl_custom_point.htm">custom_point.cpp</a>
Mapping a user defined point class to the library point_concept</li>
            <li><a href="gtl_polygon_usage.htm">polygon_usage.cpp</a>
Using the library provided polygon data types and functions</li>
            <li><a href="gtl_custom_polygon.htm">custom_polygon.cpp</a>
Mapp