These definitions can help you:
1. A silhouette is the outline of a shape.
The internal lines in a tessellation are not important.
The silhouette may contain 2 things, a horse with rider,
a devil/angel, etc.
2. A vertex is a point where 3 lines on a silhouette joint together.
A vertex is also a place where 3 adjacent shapes meet.
3. A line segment is a piece of the silhouette between two
vertices.
If the silhouette has 4 vertices, there are 4 line segments.
4. T line is a translation line.
C line is a half turn, this line can be rotated at its mid-point.
C3 line can rotate at one of the end points by 120 degrees.
C4 line can rotate at one of the end points by 90 degrees.
C6 line can rotate at one of the end points by 60 degrees.
G line has a mirror clone which may also translate and rotate.
5. With the exception of the C line, each of the above line segments must
appear in pairs on the silhouette. The C line is considered a pair by itself.
Periodic Drawings with JAVA programs
Mathematical Basis of Interlocking Shapes
