Parametric Model Fitting: Least Squares, RANSAC, and Hough Transform, Study notes of Electrical and Electronics Engineering

Parametric model fitting techniques, including least squares methods for fitting lines and curves, ransac for estimating homographies and fundamental matrices, and the hough transform for finding lines and curves in data. Critical issues such as noisy data, outliers, and missing data are addressed, as well as techniques for dealing with them. The document also covers the limitations and assumptions of each method.

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Pre 2010

Uploaded on 09/02/2009

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EECS 442 – Computer vision
Fitting methods
Reading: [HZ] Chapters: 4, 11
[FP] Chapters: 16
Some slides of this lectures are courtesy of profs. S. Lazebnik & K. Grauman
- Problem formulation
- Least square methods
-RANSAC
- Hough transforms
- Multi-model fitting
- Fitting helps matching!
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Download Parametric Model Fitting: Least Squares, RANSAC, and Hough Transform and more Study notes Electrical and Electronics Engineering in PDF only on Docsity!

EECS 442 – Computer vision Fitting methods

Reading:

[HZ] Chapters: 4, 11^ [FP] Chapters: 16

Some slides of this lectures are courtesy of profs. S. Lazebnik & K. Grauman

  • Problem formulation- Least square methods- RANSAC- Hough transforms- Multi-model fitting- Fitting helps matching!

Fitting

Goal: Choose a parametric model to

fit a certain quantity from data

  • Lines - Curves - Homographic transformation - Fundamental matrix - Shape model

H

Example: Estimating an homographic

transformation

Example: Estimating F

Example: fitting a 3D object model

Fitting

Goal: Choose a parametric model to

fit a certain quantity from data

Critical issues:

  • noisy data - outliers - missing data

A

Critical issues: noisy data

(intra-class variability)

H

Critical issues: outliers

Fitting

Goal: Choose a parametric model to

fit a certain quantity from data

Techniques:•Least square methods•RANSAC•Hough transform•EM (Expectation Maximization)

[forthcoming lecture]

Least squares methods

  • fitting a line -
    • Data:

( x

,^1 y ), …, (^1

x^ , n

yn

)

  • Line equation:

y^ i

= m x

+ bi^

  • Find (

m ,

b ) to minimize ∑

=^

=^

n i^

i

i^

b x m y

E^

1

(^2) )

(

( x^ i

,^ y

) i

y=mx+b

b

Ax

=

  • More equations than unknowns• Look for solution which minimizes

||Ax-b|| = (Ax-b)

T(Ax-b)

  • Solve • LS solution

0 ) ()

(^

=

− ∂

T x^ i

b Ax b Ax

b A

A A

x^

T

T^

1 )

(^

=

Least squares methods

  • fitting a line -

t 1 t^

A
A
A(
A^

+^ =
U
V
A^

1

1

−^

with

equal to

for all nonzero singular

values and zero otherwise

(^1) − ∑

= pseudo-inverse of A

Solving

b

A

A

A

x^

t

t^

1

(^

Least squares methods

  • fitting a line - t
V
U
A^
U
V
A^

+^

= SVD decomposition of A

  • Distance between point

( x^ n

,^ y

)^ n and line

ax+by=d

  • Find

( a

,^ b

,^ d

)^ to minimize the

sum of squared perpendiculardistances

ax+by=d

=^

=^

n i^

i

i^

d yb

xa

E^

1

(^2) )

(

( x^ i

,^ y

) i

0

N ) U U(

T^

=

data

Least squares methods model parameters

  • fitting a line -

1 || h||

to

subject || h A||

Minimize

=

T

UDV A

=

V of

column

last h^

=

A h = 0

Least squares methods

  • fitting a line -