I recently wrote a 3-D L-system program, a simple extension of the 2-D L-system program.
[ To Do: More documentation and material planned.]

For comparison, these are the corresponding two symbol Thue-Morse systems in one and two dimensions:

Note that all rules alternate in all directions, and each rule is the comlement of the other.

Thue-Morse cube, surface rendered.
Slice of a 6 generation (even) pattern. |
Above: Cross sections of 3-D Thue-Morse patterns, with the slice plane centered on a long diagonal of the pattern. The long range self-similar structure of the Thue-Morse pattern is more easily seen in this slice than in the 2-D square system's pattern. Notice the slightly lighter/darker trapezoids that repeat at different scales; it is a discrete similarity tiling.
Ted Bell showed me another to make these patterns with a triangular replacement system: it can be considered as the Thue-Morse sequence on a triangular tesselation. [To Do: Diagram the rules for a triangular construction.]
Matlab command:
>> volOut = L_System_3D_tiling( '', [ng], 2, 1, 0, '', 0, [0 1; 1 0], [1 0; 0 1], [1 0; 0 1], [0 1; 1 0] );
where [ng] is the number of generations.
Oversampled and sliced with Space Software.
Matlab command:
>> volOut = L_System_3D_tiling( '', [ng], 2, 1, 0, '', 1, [0 0; 0 0], [0 0; 0 0], [0 1; 1 1], [1 1; 1 1] );
where [ng] is the number of generations.
Oversampled and rendered with Space Software.
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Comments
slices
TM symmetries
Yes, that's right. A cube sliced through it's center on a plane perpendicular to a long diagonal.
Good question: The diagonal symmetries are the same as the 2-D TM pattern. These both start with the black symbol, the even generation ends with the black symbol, odd with white. So the even generation (left) is identical along the three diagonals (and inverted for the complementary starting symbol). The odd generation is also identical but for a mirroring about the horizontal OR a 60 degree rotation -- note that a 60 degree rotation is identical after an inversion (a swap of the symbols).
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