recovery of affine and metric properties from images in 2d projective space
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Recovery of affine and metric properties from images in 2D Projective space. 2013-03-20 Ko Dae -Won. Recovery of affine and metric properties from images in 2D Projective space. Affine properties(line at infinity) Parallelism Parallel length ratios Metric properties(circular points)

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Presentation Transcript
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Recovery of affine and metric properties from images in 2D Projective space

Affine properties(line at infinity)

  • Parallelism
  • Parallel length ratios

Metric properties(circular points)

  • Angles
  • Length ratios

Recover the original shape

1 recovery of affine properties
Homogeneous coordinates

but only 2DOF

Inhomogeneous coordinates

Recovery of affine and metric properties from images in 2D Projective space

1. Recovery of affine properties

Homogeneous coordinates

equivalence class of vectors, any vector is representative

Set of all equivalence classes in R3(0,0,0)T forms P2

Homogeneous representation of points

on

if and only if

The point x lies on the line l if and only if xTl=lTx=0

1 recovery of affine properties1
Line joining two points

The line through two points and is

Ideal points

Recovery of affine and metric properties from images in 2D Projective space

1. Recovery of affine properties

Points from lines and vice-versa

Intersections of lines

The intersection of two lines and is

Intersections of parallel lines

Line at infinity

1 recovery of affine properties2
Duality principle:

To any theorem of 2-dimensional projective geometry there corresponds a dual theorem, which may be derived by interchanging the role of points and lines in the original theorem

Recovery of affine and metric properties from images in 2D Projective space

1. Recovery of affine properties

Duality

1 recovery of affine properties3
or homogenized

or in matrix form

with

Recovery of affine and metric properties from images in 2D Projective space

1. Recovery of affine properties

Conics

Curve described by 2nd-degree equation in the plane

1 recovery of affine properties4
Recovery of affine and metric properties from images in 2D Projective space1. Recovery of affine properties

Tangent lines to conics

The line l tangent to C at point x on C is given by l=Cx

l

x

C

1 recovery of affine properties5
In general :

Recovery of affine and metric properties from images in 2D Projective space

1. Recovery of affine properties

Dual conics

A line tangent to the conic C satisfies

Dual conics = line conics = conic envelopes

1 recovery of affine properties6
Theorem:

A mapping h:P2P2is a projectivity if and only if there exist a non-singular 3x3 matrix H such that for any point in P2represented by a vector x it is true that h(x)=Hx

Definition: Projective transformation

or

Recovery of affine and metric properties from images in 2D Projective space

1. Recovery of affine properties

Projective transformations

Definition:

A projectivity is an invertible mapping h from P2 to itself such that three points x1,x2,x3lie on the same line if and only if h(x1),h(x2),h(x3) do.

projectivity=collineation=projective transformation=homography

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