Spin Image Correlation

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Spin Image Correlation

• Steven M. Kropac
• April 26, 2005

2
Presentation contents

• Overview
• Background/Motivation
• Operational Concept
• Functional Diagram
• Software Implementation
• Application
• Conclusion

3
Overview

• A spin image provides a 2D object centered
  description of a 3D mesh object.
• Essentially, a spin image represents the radial
  and elevation distances to every other vertex on
  the mesh.
• Resultant spin images can be compared
  (correlated) to identify similarities between
  vertices.

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Background/Motivation

• Object recognition for 3D computer vision has
  many applications in the area of robotics and
  automation.
• Andrew Johnson works on Surface System Guidance
  Navigation and Control for the mars science
  laboratory (2009)
• Using Spin Images for Efficient Object
  Recognition in Cluttered 3D Scenes Andrew E.
  Johnson and Martial Hebert (5/1999)
• Presents an approach for recognition of complex
  objects in cluttered 3-D scenes.
• Encoding relative positions of many points on the
  surface is not new. Others have performed
  explored using view-based approaches, or storing
  points along curves.
• The approach described in this presentation is
  different because the spin images are much more
  discriminating than curves and angles and is
  object centered, so it is not view dependant.

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Operational Concept

• Provide a Graphical User Interface (GUI) for
  loading 3D mesh models.
• Models are specified in .ply file format
• Two operations available to user
• Generate spin images for every vertex on a loaded
  3D mesh model
• Perform spin image correlation between a selected
  vertex and every other vertex on the model.
• Highly correlated vertexes will be colored bright
  green
• Vertices with limited correlation will be colored
  very dark green or black (background color).

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Functional DiagramGenerate Spin images
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Spin Image calculations

• Start with a selected vertex and associated
  normal, which we call an oriented point.
• Calculate alpha, beta distances from the oriented
  point to every other vertex.

• Alpha perpendicular distance from surface
  normal
• Beta signed perpendicular distance to the plane
  p

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Spin Image calculationsCalculating alpha,beta

• p oriented point
• n surface normal
• x position of another vertex on mesh
• Beta difference of x - p, then dot product with
  surface normal to project on Normal.
• Alpha length of vector from x to p, subtract
  out Beta component

Distance between points sum of square of
differences
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Spin Image calculationssample alpha, beta values
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Spin Image calculationsGenerate spin images

• A bin size (i,j) is selected as a multiple of the
  resolution of the mesh.
• My application uses 1x.
• The alpha,beta values are then translated to the
  appropriate bin.
• Bin dimensions might be 4x20. Alpha Beta ranges
  might be 0,2 and -3,3.
• When an alpha,beta pair is translated the
  associated bin is incremented.

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Spin Image calculationssample spin image bins
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Functional DiagramPerform Spin-image Correlation
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Spin Image CorrelationCalculating correlation
coefficient

• Correlation coefficient provides the quality of a
  least squares fitting to the selected data set.

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Software Implementatoin

• The spin image application is implemented in C
  using Microsoft Visual Studio.
• The display of 3D mesh objects is accomplished
  using OpenGL.
• A MySQL database is utilized to store calculation
  of spin images.
• Database stores (filename, vertexIndex,
  alphaBucket, betaBucket, intensityValue)
• For an image with 5000 vertices and a spin image
  size of 85x42 represents 1.8 million database
  entries.
• Spin Image calculations takes several minutes The
  amount of time is dependant on the number of
  vertices in the model.

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Spin Image Application

• The application provides the capability to parse
  .ply graphics files and display the 3D model
  using OpenGL.

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Spin Image Applicationkeyboard commands

• Left/right arrow rotate along y axis
• Up/down arrow rotate along x axis
• PgUp/PgDn rotate along z axis
• -/ zoom-out / zoom-in
• Home/end select next/previous vertex

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Spin Image ApplicationPull-down menu features

• File
• Open .ply file
• Exit
• Operation
• Calculate Spin Images and store in Database
• Display Spin Image Correlations
• View
• Zoom-in
• Zoom-out

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Spin Image ApplicationResults
Selected vertex
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Spin Image ApplicationResults (elephant)
Selected vertex

• 5 hours to generate spin images
• 10 minutes to spin-correlate

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Conclusion

• Spin images provides an interesting
  representation for surface matching.
• More work needs to be done to fully understand
  how speed issues can be addressed.
• Ex A 3D mesh has 5000 vertices. To calculate all
  spin images for this model requires 5000 5000
  25 million sets of calculations.