CS 352: PC Representation

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Intelligent Computer Graphics. Part 9 - 2. Review. ModelingAnimationData structures

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CS 352: Computer Graphics Hierarchical Graphics, Modeling, And Animation

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Overview Modeling Animation Data structures for intuitive design CSG-tree BSP-tree Quadtrees and Octrees Visibility precomputation Many figures and cases in this arrangement of addresses are from The Art of 3D Computer Animation and Imaging , by I. Kerlow

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Modeling The demonstrating issue Modeling primitives Polygon Sphere, ellipsoid, torus, superquadric NURBS, surfaces of upsets, smoothed polygons Particles Skin & bones Approaches to displaying complex shapes Tools, for example, expel, spin, hang, split, line, mix Constructive strong geometry (CSG) Hierarchy; kinematic joints Inverse kinematics Keyframes

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Representing Objects spoke to as images Defined in model directions; changed into world directions (M = TRS) glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glTranslatef(… ); glRotatef(… ); glScalef(… ); glutSolidCylinder(… );

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Primitives The essential kind of primitive is the polygon Number of polygons: tradeoff between render time and model exactness

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Spline Curves Linear spline Cardinal spline B-spline Bezier bend NURBS (non-uniform sound b-spline)

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Mesh

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Mesh disfigurements

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Sweep a shape over a way to frame a summed up chamber

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Revolution Revolve a shape around a hub to make a question with rotational symmetry

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Extrusion Extrude: grow a 2D shape in the third measurement Shape is made with a (1D) b-spline bends Hole was made by subtracting a barrel

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Joining Primitives Stitching, mixing

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Modifying Primitives

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Subdivision Surfaces Can set level of polygon subdivision

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Skin and Bones Skeleton with joined "bones" Can include "skin" top of bones Automatic or hand-tuned cleaning

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Particles

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Algorithmic Primitives Algorithms for trees, mountains, grass, hide, lightning, fire, …

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Geometric model document positions .obj: Alias Wavefront .dxf: Autocad .vrml: Inventor Dozens more Can change over between configurations Converting to a typical arrangement may lose data…

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Hierarchical models When liveliness is craved, items may have parts that move concerning each other Object spoke to as progression Often there are joints with movement limitations E.g. speak to wheels of auto as sub-articles with rotational movement (auto moves 2 pi r for every turn)

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DAG models Could utilize tree to speak to question Actually, a DAG (coordinated non-cyclic diagram) is better: can re-utilize objects Note that every bolt needs a different demonstrating change In protest situated illustrations, likewise require movement limitations with every bolt

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Example: Robot Traverse DAG utilizing DFS (or BFS) Push and pop grids en route (e.g. left-youngster right-kin) (joint position parameters?)

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Modeling Programs Moray Shareware Limited usefulness Easy Lightwave, Maya NOT shareware Very full-included Difficult to learn and utilize Moray, Maya demos; Lightwave video

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Animation Suppose you need the robot to get a container of oil to drink. How? You could set the joint positions at every minute in the liveliness ( kinematics )

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Inverse Kinematics You can't simply alter the joint changes Joint settings aren't even essentially special for a hand position! Reverse kinematics : make sense of from the hand position where the joints ought to be set.

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Using Inverse Kinematics Specify joint requirements and needs Move end effector (or question posture) Let the framework make sense of joint positions [IK demo]

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Keyframe Animation In conventional key edge liveliness the artist draws a few essential casings, and partners do the "inbetweening" or "tweening" Computer activity is likewise key-outline based At key edges, illustrator positions protests and lights, sets parameters, and so on. The framework introduces parameter values directly or along a bend To get starting with one protest posture then onto the next, reverse kinematics decide joint movements [Keyframe liveliness demo]

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Motion Capture More practical movement arrangements can be produced by Motion Capture Attach joint position markers to genuine on-screen characters Record live activity

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Morphing: easily moving starting with one picture then onto the next First advanced in a Michael Jackson video Method: a blend of Warping both pictures, bit by bit moving control focuses from area in first picture to area in the second Cross-blurring from first picture grouping to second

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3D Morphing Define 3D previously, then after the fact shapes as e.g. NURBS surfaces with same number of control focuses Gradually move control indicates from first setting second Specify key postures: e.g. grin, scowl, 12 casings of strolling movement

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Combined methodologies

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Example: virtual puppetry Suppose you need to show virtual manikin indicates How would you be able to quicken manikin developments? How might you be able to control the livelinesss remotely?

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Character Animation To make PC representation (or toon drawings) wake up …

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Personality through Pose, Expression, Motion, Timing

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Object-arranged Graphics Higher in the programming pecking order: control models with protest situated projects robot robbie; robbie.smile(); robbie.walk(270, 5, 3);

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Data Structures for Modeling This some portion of section: how some case applications be done effectively ( i.e. themes without a superior home… ) Tree-based subdivisions of space Example 1: how to speak to complex items made up of union, crossing point, contrast of different articles

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CSG Tree

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Application 2: HSR How to render in 3D with concealed surface evacuation when you don't have an equipment profundity support? Could you think about some other methods for evacuating shrouded surfaces rapidly? Rule: a polygon can't be impeded by another polygon that is behind it.

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BSP-tree The painter's calculation for concealed surface evacuation works by drawing all appearances, from back to front How to get a posting of the countenances in back-to-front request? Placed them into a double tree and cross the tree (however in what arrange?)

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BSP Tree Figures Right is "front" of polygon; left is "back" In and Out hubs demonstrate districts of space inside or outside the protest (Or, simply store split bits of polygons at leaves)

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Traversing a BSP tree Binary Space Partition tree : a paired tree with a polygon at every hub Children in left subtree are behind polygon Children in right subtree are before polygon Traversing a BSP-tree: If invalid pointer, do nothing Else, draw far subtree, then polygon at current hub, then close subtree Far and close are dictated by area of viewer Runtime of traversal? Disadvantages?

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Building a BSP tree Inserting a polygon: If tree is unfilled make it the root If polygon to be embedded converges plane of polygon of current hub, split and embed half on every side recursively. Else embed on proper side recursively Problem: the quantity of countenances could develop significantly Worst case (O(n 2 ))… yet normally it doesn't become too gravely by and by…

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BSP-tree Summary Returns polygons not really in sorted request, but rather in a request that is right for back-to-front rendering Widely utilized when Z-support equipment may not be accessible (e.g. amusement motors) Guarantees back-to-front rendering for alpha mixing Works well (direct time traversals) in the quantity of split polygons [And we trust the quantity of polygons doesn't develop a lot through splitting]

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Application 3: Handling Large Spatial Data Sets Example application: picture based rendering Suppose you have numerous advanced pictures of a scene, with profundity data for pixels How to discover proficiently the focuses that are in front? Different applications: Speeding up beam following with numerous items Rendering shapes of 3D volumetric information, for example, MRI filters

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Quadtree: partition space into four quadrants. Check as Empty, Full, or Partially full. Recursively subdivide mostly full districts Saves much time, space more than 2D pixel information!

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Quadtree Structure

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Octrees Generalize to cutting up a solid shape into 8 sub-3D squares, each of which might be E, F, or P (and subdivided) Much more productive than a 3D exhibit of cells for 3D volumetric information

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Quadtree Algorithms How might you render a quadtree shape? discover the crossing point of a beam with a quadtree shape? Take the union of two quadtrees? Crossing point? Discover the neighbors of a cell?

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Applications of Octrees Contour finding in MRI information 3D filtering and rendering Efficient beam following Intersection, impact testing

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Research in Visibility Can we make sense of ahead of time what will be obvious from every perspective?

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Viewer-focused representation Viewer-focused protest representations: representation not of volume of space filled but rather appearance from all perspectives

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Occlusion in view space Occlusion in view space is subtraction

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Events: limits in perspective space where faces show up or vanish

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Aspect Graph Aspect diagram: a chart with a hub for each topologically particular perspective of a question, with edges associating neighboring perspectives

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Aspect diagram assortments Aspect charts can be built for 3D: space 2D: various hub turns or planar movements 1D: single-pivot revolutions

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1D Aspect Graph for Rotation

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1D Aspect Graph Results Useful for revolutions without Z-cradle equipment! Not all that valuable for additional

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