Lecture-15-h - Lecture-15 Quad Trees, Chain Code, Shape...

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Unformatted text preview: Lecture-15 Quad Trees, Chain Code, Shape number & Moravec’s interest operator Quad Trees • • • • Data structure to represent regions Three types of nodes: gray, black and white First generate the pyramid, then: If type of pyramid is black or white then return else – – – – – Recursively find quad tree of SE quadrant Recursively find quad tree of SW quadrant Recursively find quad tree of NE quadrant Recursively find quad tree of NW quadrant Retrun 1 Chain Code • A simple technique to represent a shape of boundary. • Each directed line segment is assigned a code. • Chain code is integer obtained by putting together the codes of all consecutive line segments. • Shape number is a normalized chain code, which is invariant to translation and rotation. 2 3 Moravec’s Interest Operator Algorithm • Compute four directional variances in horizontal, vertical, diagonal and antidiagonal directions for each 4 by 4 window. • If the minimum of four directional variances is a local maximum in a 12 by 12 overlapping neighborhood, then that widow (point) is interesting. 4 3 2 Vh = Â Â ( P( x + i, y + j ) - P( x + i + 1, y + j )) 2 j =0 i =0 2 3 Vv = Â Â ( P( x + i, y + j ) - P( x + i, y + j + 1)) 2 j =0 i =0 2 2 Vd = Â Â ( P( x + i, y + j ) - P( x + i + 1, y + j + 1)) 2 j =0 i =0 2 3 Va = Â Â ( P( x + i, y + j ) - P( x + i - 1, y + j + 1)) 2 j = 0 i =1 5 3 2 Vh = Â Â ( P( x + i, y + j ) - P( x + i + 1, y + j )) 2 j =0 i =0 2 3 Vv = Â Â ( P( x + i, y + j ) - P( x + i, y + j + 1)) 2 j =0 i =0 2 2 Vd = Â Â ( P( x + i, y + j ) - P( x + i + 1, y + j + 1)) 2 j =0 i =0 2 3 Va = Â Â ( P( x + i, y + j ) - P( x + i - 1, y + j + 1)) 2 j = 0 i =1 V ( x, y ) = min(Vh ( x, y ),Vv ( x, y ),Vd ( x, y ),Va ( x, y )) Ï1 ifV ( x, y )local max I ( x, y ) = Ì 0 0therwise Ó 6 Books by Hans Moravec • Robot Rover Visual Navigation • Mind Children: The future of Robot and Human Intelligence • Robot, Being – Website http://www.frc.ri.cmu.edu/~hpm/ 7 New Book Cart under SAIL 8 1979 and 1997 3D Maps from stereo NAVLABS 9 Beast Universal Delivery 10 Potsdam Home Vacuum Cleaning Robot (Dustbot) 11 Home Vacuum Cleaning Robot (Dustbot) 12 13 14 ...
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This note was uploaded on 06/12/2011 for the course CAP 5415 taught by Professor Staff during the Fall '08 term at University of Central Florida.

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