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Finding “Lines” of Symmetry on 3D Craniofacial Meshes

Method• Compute descriptors of each mesh vertex•From these descriptors, learn areas that may be related to certain landmarks• cluster learned areas for a given landmark• find pairs of clusters for landmarks that appear on both sides of the center (e.g. eye corners, mouth corners)• find clusters that appear in the middle• evaluate goodness of such clusters• choose the best ones and use to find the symmetry line

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We learned the en areas and symmetry

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Now we try 10 separate landmarks.

• 10 areas learned– Ten models– Nose: acal (nose side), prn, sn,se– Eyes: en, ex– Mouth: lils, ch, sto– Chin: slab

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acal

prn

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se

sn

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en

ex

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lils

sto

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Ch

slab

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• Cluster on selected areas based on position

acal prn se

sn en

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• Cluster on selected areas based on position

ex slab lils

ch sto

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Using landmarks given by doctors as a standard to define D_plane

• For 22qDS data, we have doctor marked points. From their landmarks, computer the symmetrical plane

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How to define “good” symmetric clusters

• A “good” pair of clusters should be symmetric to the plane

• A “good” single cluster should have the center on the plane

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• Select a “good” symmetry pair (or single area)

acal prn se

sn en

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• Select a “good” symmetry pair (or single area)

ex slab lils

ch sto

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Procedure for New Images

• Select possible landmark areas (from learning)• Clustering• Pair clusters• Classify “good symmetry”• Get center and draw a plane using learned

centers

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Select possible landmark areas

acal prn se

sn en

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Select possible landmark areas

ex slab lils

ch sto

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Cluster and Pair clusters

acal prn se

sn en

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Cluster and Pair clusters

ex slab lils

ch sto

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Classify “good symmetry”

acal prn se

sn en

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Classify “good symmetry”

ex slab lils

ch sto

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Get all the centers for good pairs and single ones

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Using only the “inliers” to get the symmetry plane

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Final result: pre-op 4days female unilateral CL

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Result: pre-op 3 wks female CLP

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Result: pre-op 3m female CLP