applications of computational geometry
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Applications of Computational Geometry. COSC 2126 Computational Geometry. Outline. General categories of computational geometry application domains. Triangulation and meshing Geocomputation Computational biology. Application Domains. Computer graphics 2-D and 3-D intersections. - PowerPoint PPT PresentationTRANSCRIPT
Applications of Computational Geometry
COSC 2126COSC 2126Computational GeometryComputational Geometry
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Outline
General categories of computational geometry application domains.
Triangulation and meshing Geocomputation Computational biology
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Application Domains
Computer graphics 2-D and 3-D intersections. Hidden surface elimination. Ray tracing.
Virtual reality Collision detection (intersection).
http://www.linuxgraphic.org/section3d/articles/raytracing/images/theiere.jpg
http://graphics.cs.uni-sb.de/Publications/2006/RTG/spheres.jpg
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Application Domains (2)
Robotics Motion planning, assembly
orderings, collision detection, shortest path finding
Global information systems (GIS) Large data sets data
structure design. Overlays Find points in
multiple layers. Interpolation Find
additional points based on values of known points.
Voronoi diagrams of points.
Spatial elevation modelhttp://mathworld.wolfram.com/VoronoiDiagram.htmlhttp://skagit.meas.ncsu.edu/~helena/classwork/topics/F1a.gif
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Application Domains (3)
Computer aided design and manufacturing (CAD / CAM) Design and manipulate 3-D objects.
Possible manipulations: merge (union), separate, move.
“Design for assembly” CAD/CAM provides a test on objects for ease of
assembly, maintenance, etc. Computational biology
Determine how proteins combine together based on folds in structure.
Surface modeling, path finding, intersection.
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Triangulation and Meshing
Used to generate surfaces and solids from unstructured data (point clouds). Surfaces triangles Solids tetrahedra
Important in most sciences: Medical imaging. Engineering – finite element modeling. Art. Computer games.
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Delaunay Triangulation
Delaunay triangulation for a set P of points in the plane is a triangulation DT(P) s.t. no point in P is inside the circumcircle of any triangle in DT(P).
The Delaunay triangulation of a discrete point set P corresponds to the dual graph of the Voronoi tessellation for P.
For a set P of points in d-dimensional Euclidean space, DT(P) is s.t. no point in P is inside the circum-hypersphere of any simplex in DT(P).
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Finite Element Method
http://www.grc.nasa.gov/WWW/RT/2003/7000/7740morales.html
Stress distributions on the foot.
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FEM (2)
Truck crash simulation.
http://en.wikipedia.org/wiki/Finite_element_method
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Photorealism in Computer Graphics
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Meshing in Game Graphics
http://www.gamingtarget.com/images/media/Specials/Essential_Tech_Terminology_For_Gamers/page/p002.jpghttp://graphics.ethz.ch/~mattmuel/projects/project.htm
http://www.math.tu-berlin.de/geometrie/gallery/vr/bilder/FarCry0001.jpg
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Meshing in Game Graphics (2)
Finding Next Gen – CryEngine 2, Martin Mittring14, Crytek GmbH
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Surface Reconstruction With Radial Basis Functions
Scanning a bone section with a laser
scanner.
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Surface Reconstruction With Radial Basis Functions (2)
Point cloud
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Surface Reconstruction With Radial Basis Functions (3)
Final surface
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Scattered Point Interpolation with Radial Basis Functions
Courtesy: Derek Cool, Robarts Research Imaging Laboratories
Interpolate scattered
points
Radial basis interpolation
Surface normals Final RBF model
Original point cloud from segmented contours in CT volume.
Enhanced point cloud
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Geocomputation
Geocomputation – a new paradigm for multidisciplinary/interdisciplinary research that enables the exploration of extremely complex and previously unsolvable problems in geography.
Used to study spatial data: Population distributions. Movement patterns of migratory animals. Locations of natural resources. Epidemiology. Source and extent of environmental pollution and
contamination. Extent of natural disasters. Many other applications.
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Geocomputation (2)
Geocomputation depends on the contributions of many fields of study: Computational geometry. Interactive exploratory data analysis. Data mining. Numerical methods. Graphics and visualization.
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Geographic Information Systems
Also known as geomatics – the application of computational methods and systems to geographical problems.
Computational geometry provides useful tools and algorithms for GIS, including: Data correction (after data acquisition and input). Data retrieval (through queries). Data analysis (e.g map overlay and geostatistics). Data visualization (for maps and animations).
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Global Positioning System (GPS)
Global positioning system (GPS) – A specialized, dedicated distributed system for determining geographical position anywhere on Earth.
Satellite-based system launched in 1978. Initially for military applications, but extended
for civilian use (traffic navigation), and other tracking uses.
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GPS (2)
29 satellites, each circulating in an orbit at height 20,000 km, and having up to four regularly calibrated atomic clocks.
Each satellite (i) continuously broadcasts its position (xi, yi, zi), and timestamps each message.
This allows every receiver on Earth to accurately compute its own position using three satellites.
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Location Calculation
For the GPS receiver to locate itself, two data are needed: The location of at least 3 reference satellites. The distance between the receiver and each of those satellites.
The receiver obtains both of these by analyzing high-frequency, low-power radio waves from the GPS satellites.
Because radio waves travel at the speed of light, receivers can calculate the distance the wave traveled by the amount of time it took to travel.
Each GPS receiver contains a database of the locations of each satellites at a given time.
Using this information, the receiver uses trilateration to find the exact spot on earth.
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GPS (3)
Computing a position in a two-dimensional space.
(Altitude)
(Earth’s surface at sea level)
Trilateration – a method for determining the intersections of three sphere surfaces given the centers and radii of the three spheres.
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Time Calculation
Each satellite tracks time by an atomic clock. They are all synchronized.
Upon receiving the signal from the satellites, the receiver can calculate the time delay of each, providing the travel time.
By multiplying the travel time by the speed of light, the distances of the satellites are obtained.
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GPS (4)
Principle of intersecting circles can be re-formulated to 3D.
Three (3) satellites are needed to compute the longitude, latitude, and altitude of a receiver on Earth.
Real world facts that complicate GPS:1. Some time elapses before data on a
satellite’s position reaches the receiver.2. The receiver’s clock is generally not
synchronized to the satellite.
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Computing Position Using GPS
r: Deviation of receiver’s clock from the actual time.
Ti: Timestamp received from satellite i.
di: Real distance between the receiver and satellite i.
222 )()()( ririririnowi zzyyxxTTcd
However,
4 equations (3 satellites + time difference) are needed to solve for four unknowns, xr, yr, zr, and r.
GPS can also be used for synchronization.
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Limitations of CG w.r.t. GIS
Computational geometry algorithms are often very complex, and require a large effort to implement.
Efficiency analysis, which is based on worst-case inputs to the algorithm, is often performed. The theoretical worst-case data sets may be rather
artificial, and never appear in real-world applications. Another problem lies in the abstraction of the original
problem, in which several criteria to be met “at least to some extent” simultaneously. This leads to vague problem statements, but CG
generally considers well-defined, simple-to-state problems.
This problem will be more difficult than the first two.
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Bioinformatics – Protein Folding
Proteins are large 3D molecules with complicated geometries and topologies.
Basic idea – Create “designer proteins” that can be used to treat a variety of disease conditions.
Lock-and-key mechanism – proteins have binding sites where other ions or molecules form chemical bonds.
Proteins can therefore bind to harmful pathogens (e.g. viruses), rendering them harmless.
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Protein Binding to a Pathogen
www.physorg.com/news138885789.html
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3-D curve{vi}, i = 1…n
Geometric Representation of Proteins – Primary Structure
The primary structure of a protein is its sequence of amino acids, which determines what the protein does, how it interacts with other proteins, and how it folds.
Sequence of amino acids and peptide bonds.
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Geometric Representation of Proteins – Secondary Structure Secondary structure refers to the way a single
protein (macromolecule) folds together. Secondary structure consists of helix (helices),
strand(s), and random coil(s).
http://mcl1.ncifcrf.gov/integrase/asv_secstr.html
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Geometric Representation of Proteins – Tertiary Structure Tertiary structure refers to the protein’s 3D shape. It is determined by the protein’s primary structure.
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Geometric Representation of Proteins – Quaternary Structure Quaternary structure refers to the arrangement of
multiple folded protein molecules in a multi-subunit complex.
http://www.cryst.bbk.ac.uk/PPS2/course/section12/haemogl2.html
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The “grand challenge” in bioinformatics and proteomics.
Allows the transition from sequence to structure.
Currently, relatively simple computational folding models have proven to be NP complete even in the 2D case!
Example.
Protein Folding
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Other Non-Traditional Applications
Spatial databases. Radiation therapy planning. Computational topology.
Use of geometry and topology to study complex and massive data sets.
Applications range from medical, GIS, CAD/CAM, and crystallography to financial and economic models, music, and quantum computing.
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