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Models and Matching

Models and Matching. Methods of modeling objects and their environments; Methods of matching models to sensed data for recogniton. Some methods to study. Mesh models ( surface ) Vertex-edge-face models ( surface ) Functional forms: superquadrics ( surface ) Generalized cylinders ( volume )

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Models and Matching

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  1. Models and Matching Methods of modeling objects and their environments; Methods of matching models to sensed data for recogniton CSE 803

  2. Some methods to study • Mesh models (surface) • Vertex-edge-face models (surface) • Functional forms: superquadrics (surface) • Generalized cylinders (volume) • Voxel sets and octrees (volume) • View class models (image-based) • Recognition by appearance (image-based) • Functional models and the Theory of affordances (object-oriented) CSE 803

  3. Models are what models do CSE 803

  4. What do models do? CSE 803

  5. Vertex-edge-face models Polyhedra and extensions; Model the surface of objects CSE 803

  6. Vertex-Edge-Face model CSE 803

  7. Sample object All surfaces are planar or cylindrical CSE 803

  8. Matching methods • Hypothesize point correspondences • Filter on distances • Compute 3D alignment of model to data • Verify positions of other model points, edges, or faces. You can now do this! • LOTS of work in the literature on this! Can work for many industrial objects (and human faces perhaps!) CSE 803

  9. Triangular meshes Very general and used by most CAD systems. CSE 803

  10. Texture-mapped mesh dog SURFACE PLUS TEXTURE 3D SURFACE MODEL With each triangle is a mapping of its vertices into pixels [r, c] of a color image. Thus any point of any triangle can be assigned a color [R, G, B]. There may be several images available to create these mappings. Courtesy of Kari Puli CSE 803

  11. Meshes are very general They are usually verbose and often are too detailed for many operations, but are often used in CAD. (Volumetric cube models are actually displayed here: made from many views by Kari Pulli.) CSE 803

  12. Mesh characteristics + can be easy to generate from scanned data CSE 803

  13. Making mesh models CSE 803

  14. Marching cubeshttp://www.exaflop.org/docs/marchcubes/ (James Sharman) Raster scan through image F(r, c). Look for adjacent pixels, one above threshold and one below threshold. Interpolate real coordinates for f(x, y) = t in between "Marching Cubes: A High Resolution 3D Surface Construction Algorithm",William E. Lorensen and Harvey E. Cline,Computer Graphics (Proceedings of SIGGRAPH '87), Vol. 21, No. 4, pp. 163-169. CSE 803

  15. Marching in 3D space F(s, r, c) Some voxel corners are above threshold t and some are below. CSE 803

  16. PhD work by Paul Albee 2004 • Used Argonne National Labs scanner • High energy, high resolution planar Xrays penetrate object rotating on a turntable • Computer aided tomography synthesizes a 3D volume of densities with voxel size of about 5 microns CSE 803

  17. Segmentation of Scutigera a tiny crablike organism Slice j of material density F( sj, r, c ) “thresholded” volume CSE 803

  18. Some common 3D problems • analyze blood vessel structure in head • capture structure and motion of vertebrae of spine • analyze porosity and structure of soil • analyze structure of materials • automatic segmentation into regions • automatic correspondence of 3D points at two instants of of time • 3D volume visualization and virtual tours CSE 803

  19. Scanning technique abstraction CCD camera (row) material sample X-ray planes scintillator Pin head X-rays partly absorbed by sample; excite scintillator producing one row in the camera image; rotate sample a few degrees and produce another row; 3D reconstruction using CT rotate CSE 803

  20. Scutigera: a tiny crustacean • organism is smaller than 1 mm • scanned at Argonne • volume segmented and • meshed by Paul Albee • roughly ten million triangles • to represent the surface • anaglyph created for 3D • visualization • (view with stereo glasses) CSE 803

  21. Presentation of Results to User • Can explore the 3D data using rotation/translation • Can create stereo images from 3D data CSE 803

  22. Physics-based models Can be used to make meshes; Meshes retain perfect topology; Can span spots of bad or no data CSE 803

  23. Physics-based modeling CSE 803

  24. Forces move points on the model; halt at scanned data CSE 803

  25. Fitting an active contour to image data CSE 803

  26. Balloon model for closed object surface Courtesy of Chen and Medioni CSE 803

  27. Balloon evolution • balloon stops at data points • mesh forces constrain neighbors • large triangles split into 4 triangles • resulting mesh has correct topology • hard CS part is detecting when balloon should be stopped by data point CSE 803

  28. Physics-based models Can also model dynamic behavior of solids (Finite Element Methods) CSE 803

  29. Tagged MRI: 3D interest points can be written to body! The MRI sensor tags living tissue and can sense its movement. Motion of a 3D tetrahedral finite elements model can then be analyzed. FMA model attempts to model the real physics of the heart. Work by Jinah Park and Dimitry Metaxes. CSE 803

  30. Algorithms from computer graphics make mesh models from blobs • Marching squares applied to some connected image region (blob) • Marching cubes applied to some connected set of voxels (blob) • See a CG text for algorithms: see the visualization toolkit for software CSE 803

  31. The octree for compression CSE 803

  32. Generalized cylinders CSE 803

  33. Generalized cylinders • component parts have axis • cross section function describes variation along axis • good for articulated objects, such as animals, tools • can be extracted from intensity images with difficulty CSE 803

  34. Extracting a model from a segmented image region Courtesy of Chen and Medioni CSE 803

  35. Interpreting frames from video • Can we match a frame region to a model? • What about a sequence of frames? • Can we determine what actions the body is doing? CSE 803

  36. Modeling the human body for clothing industry and … Multiple Structured light scanners used: could this be a service industry such as Kinkos? Actually cross sections of a generalized cylinder model. CSE 803

  37. Generalized cylinders CSE 803

  38. View class models Objects modeled by the distinct views that they can produce CSE 803

  39. “aspect model” of a cube CSE 803

  40. Recognition using an aspect model CSE 803

  41. View class model of chair 2D Graph-matching (as in Ch 11) used to evaluate match. CSE 803

  42. Side view classes of Ford Taurus (Chen and Stockman) These were made in the PRIP Lab from a scale model. Viewpoints in between can be generated from x and y curvature stored on boundary. Viewpoints matched to real image boundaries via optimization. CSE 803

  43. Matching image edges to model limbs Could recognize car model at stoplight or gate or in car wash. CSE 803

  44. Appearance-based models Using a basis of sub images; Using PCA to compress bases; Eigenfaces (see older .pdf slides 14C) CSE 803

  45. Function-based modeling Object-oriented; What parts does the object have; What behaviors does it have; What can be done with it? (See plastic slides of Louise Starks’s work.) CSE 803

  46. Louise Stark: chair model • Dozens of CAD models of chairs • Program analyzes model for * stable pose * seat of right size * height off ground right size * no obstruction to body on seat * program would accept a trash can (which could also pass as a container) CSE 803

  47. Theory of affordances: J.J. Gibson • An object can be “sittable”: a large number of chair types, a box of certain size, a trash can turned over, … • An object can be “walkable”: the floor, ground, thick ice, bridge, ... • An object can be a “container”: a cup, a hat, a barrel, a box, … • An object can be “throwable”: a ball, a book, a coin, an apple, a small chair, … CSE 803

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