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3D Screen-space Widgets for Non-linear Projection

3D Screen-space Widgets for Non-linear Projection. Patrick Coleman, Karan Singh (Univ of Toronto) Nisha Sudarsanam, Cindy Grimm (Washington Univ in St. Louis) Leon Barrett (Univ of Calif, Berkeley). What is non-linear perspective?. Perception uses locally linear perspective

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3D Screen-space Widgets for Non-linear Projection

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  1. 3D Screen-space Widgets for Non-linear Projection Patrick Coleman, Karan Singh (Univ of Toronto) Nisha Sudarsanam, Cindy Grimm (Washington Univ in St. Louis) Leon Barrett (Univ of Calif, Berkeley)

  2. What is non-linear perspective? • Perception uses locally linear perspective • Depth, placement in scene • Fovea only encompasses a small number of degrees • 3D sense built out of saccades • Artists use this fact to make better use of 2D canvas • Local perspective maintained • Continuity between local perspectives Marie Cassett Graphite 2005, 12/1/2005

  3. What does this mean? Graphite 2005, 12/1/2005

  4. Mechanics • Define more than one camera Ci • Define region of influence of each camera wi • Use blended combination of cameras • Different camera for each vertex • (Dual of free-form deformation) • Blend matrices, projected point, camera parameters… Karan Singh, A Fresh Perspective, Graphics Interface 2002 Graphite 2005, 12/1/2005

  5. It’s all in the user interface… • Each camera has 11 degrees of freedom • 6 for pose (position, orientation) • 5 internal (zoom/focal length, center of projection, skew, aspect ratio) • Using n cameras implies 11n parameters… • One mouse Graphite 2005, 12/1/2005

  6. Some observations • Scene should have some coherency • Dominant (default) view • Other cameras are small, local changes to default view • Bow the wall out • Changes happen in screen space • Can be sketched • Simple geometry Graphite 2005, 12/1/2005

  7. Basic approach • Use geometric proxies • Lines, points, boxes • Image-space change controls camera change • Point moves, camera pans • Also controls region of influence of new camera Graphite 2005, 12/1/2005

  8. Flow • User picks default view (may pick more than one) • Draws geometric proxies • Defines 3D and 2D geometry • User edits 2D proxies • System solves for new cameras • Displays result Graphite 2005, 12/1/2005

  9. Changing weight of camera • User can then edit the region of influence of each camera • 3D implicit volume Graphite 2005, 12/1/2005

  10. Remainder of talk • Description of geometric proxies • Simple (lines, points) • Combined • Special purpose (fish-eye, panorama) • Mechanics of camera solving Graphite 2005, 12/1/2005

  11. Simple proxies • Point • Causes camera pan • Line • Moving causes pan • Changing orientation rotates camera • Changing size changes zoom Graphite 2005, 12/1/2005

  12. Complex proxies • Wedge (two lines) • Position, orientation, size as before • Angle changes perspective Graphite 2005, 12/1/2005

  13. Complex proxies, cont • Two lines • Position, orientation, size as before • Changing relative size (rotation) • Changing relative angle (perspective) Graphite 2005, 12/1/2005

  14. Complex proxies, cont • Cube edge Graphite 2005, 12/1/2005

  15. Complex proxies, cont. • Bounding box • Size: zoom • Position: pan Graphite 2005, 12/1/2005

  16. Mixing proxies • Wedge plus bounding box • Wedge controls orientation • Bounding box controls size, position • Wedge and wedge • Line and wedge • … • Still solves for single camera Graphite 2005, 12/1/2005

  17. Outer box Original inner box New box Continuous camera change • Fish-eye • Two boxes, outer controls region of influence • Inner controls amount of zoom • Zoom smoothly Graphite 2005, 12/1/2005

  18. Continuous camera change • Line to curve • Sequence of position, orientation changes • Line segments • Project point to line to determine how much to pan Graphite 2005, 12/1/2005

  19. Solver • Proxy + edit defines allowable camera changes • E.g., pan allows only translation in film plane • Proxy defines error metric • E.g., point constraint is distance of projected point from desired image point • Find camera that minimizes error metric • Simplex, or amoeba, solver Inverse kinematics approach: Through the Lens Camera Control, Gleicher, Siggraph 1992 Graphite 2005, 12/1/2005

  20. Camera degrees of freedom • Translate in film plane direction • Proxy moved in image plane • Focal length • Change in scale • Translate in/out • Proxy changed perspective • Rotate/spin around look vector • Proxy rotated in film plane • Rotate left/right, up/down • Asymmetric change in proxy Graphite 2005, 12/1/2005

  21. User control • Camera parameters to interpolate • Skew, center of projection, aspect ratio • Importance of matching each geometric proxy • Region of influence of camera • Grouping of proxies Graphite 2005, 12/1/2005

  22. Summary • Non-linear projection difficult to control • Tool box for specifying camera changes • Image-based • Default view editing • Proxies also provide natural region-of-influence • Still cumbersome Graphite 2005, 12/1/2005

  23. Future work • Sketch-based, global widgets Graphite 2005, 12/1/2005

  24. Graphite 2005, 12/1/2005

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