TICK RINGS

你可以设置一系列的刻度，当你有多条轨道的时候

<tick>
# drawn at one radius
radius = dims(ideogram,radius_outer)
...
</tick>

<tick>
# drawn at two radii
radius = dims(ideogram,radius_outer)
radius = 0.8r
...
</tick>

<tick>
# drawn at three radii
radius = dims(ideogram,radius_outer)
radius = 0.8r
radius = 0.6r
...
</tick>

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