For a straight line make a point coincide with the previous one and the next
point coincide with the following one. Example:
<point1>, <point2>, ... <point7>, <point7>, <point8>, <point8>, <point9>
etc.
For an edge, use
...<point3>, <point4>, <point4>, <point5>, etc...
If this doesn't help, consult Chris Colefax's spline include file
documentation.
