Houdini L System Turtle Commands
http://www.sidefx.com/docs/houdini/nodes/sop/lsystem.html
A, B, C, X, Y, Z etc. variables
F move forward
f move forward without drawing
+ turn right
– turn left
[ ] create a branch
: percent chance
& pitch up
^ pitch down
\ roll clockwise
/ roll counter clockwise
” scale branch length
! in(x,y,z) prune branch length
% end branch
T tropism (gravity)
J K M insert geo