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3D Shape Descriptors: 4D Hyperspherical Harmonics “ An Exploration into the Fourth Dimension ”. By: Bryan Bonvallet Nikolla Griffin Advisor: Dr. Jia Li. Introduction: The Problem. Increased availability of 3D shapes Text based searches are not effective
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3D Shape Descriptors: 4D Hyperspherical Harmonics“An Exploration into the Fourth Dimension” By: Bryan Bonvallet Nikolla Griffin Advisor: Dr. Jia Li
Introduction: The Problem • Increased availability of 3D shapes • Text based searches are not effective • Robust for simple and complex applications
Shape Descriptors • Definition: Computational 3D shape representation • Characteristics • Easy comparison • Independent of original representation • Concise to store • Insensitive to noise • Challenges • Rotation • Translation • Scale
3D Spherical Harmonics • Benefits • Invariant to scale and rotation • Relatively invertible • High precision/ recall • Process • Voxelize • Cut along radius • Analyze harmonics • Problems • 3D storage • Error due to radii cuts • Harmonic truncation
Comparison Method • Precision • Fraction of retrieved images which are relevant • Recall • Fraction of relevant images which are retrieved • Example • 20 cows total • 30 results • 10 results are cows • Precision = 1/3 • Recall = 1/2
4D Hyperspherical Harmonics • Theory Basis • Want harmonics over entire shape • No slicing across radii • n-sphere harmonics • 2D plane to 3D sphere mapping
4D Hyperspherical Harmonics • Theory • 3D volume to 4D hypersphere mapping • Hyperspheric harmonic analysis • No radii cuts
4D Spherical Harmonics Voxelization Cartesian Coordinates Discreet Cartesian Continuous: 4D Unit Sphere Hyperspherical Coordinate continuous 4D Harmonic Coefficients
Conclusion • Inconclusive • we are using a square matrix for solving coefficients (LU decomposition algorithm for solving Ax=b) • we can only sample a fixed number of points • we cannot use the entire sample set of points
Future Work • Use SVD algorithm for solving Ax=b
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