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Departement Ingenieur. Industrieel Bouwkunde. afdeling. S Y L L A B U S P H O T O G R A M M E T R Y MODULE 4: INTRODUCTION TO THE USE OF SCALEDRECTIFIED PHOTOGRAPHY AND PANORAMIC PHOTOGRAPHY. Projection. Projection. Vertical vanishing point (at infinity).

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Departement

Ingenieur

Industrieel

Bouwkunde

afdeling

S Y L L A B U S

P H O T O G R A M M E T R Y

MODULE 4: INTRODUCTION TO THE USE OF

SCALEDRECTIFIED PHOTOGRAPHY AND PANORAMIC

PHOTOGRAPHY




Vanishing points

Vertical vanishing

point

(at infinity)

Vanishing

line

Vanishing

point

Vanishing

point

Vanishing Points

Slide from Efros, Photo from Criminisi



Vanishing point calibration
Vanishing point calibration

  • Advantages:

    • only need to see vanishing points(e.g., architecture, table, …)

  • Disadvantages:

    • not that accurate

    • need rectahedral object(s) in scene

Structure from Motion


Resectioning
Resectioning

Resectioning: correspondence between 3D and image entities



Image formation
Image formation

  • Let’s design a camera

    • Idea 1: put a piece of film in front of an object

    • Do we get a reasonable image?


Pinhole camera
Pinhole camera

  • Add a barrier to block off most of the rays

    • This reduces blurring

    • The opening known as the aperture

    • How does this transform the image?


Camera obscura
Camera Obscura

  • The first camera

    • Known to Aristotle

    • How does the aperture size affect the image?


Adding a lens

“circle of

confusion”

Adding a lens

  • A lens focuses light onto the film

    • There is a specific distance at which objects are “in focus”

      • other points project to a “circle of confusion” in the image

    • Changing the shape of the lens changes this distance


Lenses
Lenses

  • A lens focuses parallel rays onto a single focal point

    • focal point at a distance f beyond the plane of the lens

      • f is a function of the shape and index of refraction of the lens

    • Aperture of diameter D restricts the range of rays

      • aperture may be on either side of the lens

    • Lenses are typically spherical (easier to produce)

F

focal point

optical center

(Center Of Projection)


Thin lenses
Thin lenses

  • Thin lens equation:

    • Any object point satisfying this equation is in focus

    • What is the shape of the focus region?

    • How can we change the focus region?

    • Thin lens applet: http://www.phy.ntnu.edu.tw/java/Lens/lens_e.html (by Fu-Kwun Hwang )


Depth of field
Depth of field

  • Changing the aperture size affects depth of field

    • A smaller aperture increases the range in which the object is approximately in focus

f / 5.6

f / 32

Flower images from Wikipedia http://en.wikipedia.org/wiki/Depth_of_field


Range of tools

Digital Survey > Dimensional> indirect (photographic)

Scaled-rectified photography:

1. Referencing

Total Station

To measure

Controls: Targets for

rectified

photography

(b)

(a)

(b)

The Total station is located

by indicated location (a)

and orientation (b)

(a)

Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm


Range of tools

Digital Survey > Dimensional> indirect (photographic)

Scaled-rectifiedphotography:

2. Measuring

controls

Controls: Targets for rectified

photography are measured with

the total station

Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm


Range of tools

Digital Survey > Dimensional> indirect (photographic)

Scaled-rectifiedphotography:

2. Measuring

controls

If a total station is not available,

we can triangulate the controls,

measure them by disto or tape

Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm


Range of tools

Digital Survey > Dimensional> indirect (photographic)

Scaled-rectifiedphotography:

3. Taking a

parallel

photography

A photo is taken covering

the fabric with 5 targets

Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm


Range of tools

Digital Survey > Dimensional> indirect (photographic)

Scaled-rectifiedphotography:

Specialized

Software

5. Reducing the distorion of the photography

Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm


TECHNOLOGY:

Digital Survey > Dimensional> indirect (photographic)

Scaled-rectifiedphotography:

6. Results: digitizing the photograph

Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm


KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA

RECTIFIED PHOTOGRAPHY

NOT RECOMMENDED FOR

Irregular surfaces - Circular surfaces

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MODULE 4: SCALERECT-PHOTO


KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA

RECTIFIED PHOTOGRAPHY

Surfaces

1

Each surface requires

recti cation

1

2

3

4

5

2

3

4

5

5

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MODULE 4: SCALERECT-PHOTO


KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA

RECTIFIED PHOTOGRAPHY

Reducing perspective distortion

Vertical tilt of camera is not recommended

Optimal position

Slide courtesy of Christian Ouimet, Public Works Canada

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MODULE 4: SCALERECT-PHOTO


KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA

RECTIFIED PHOTOGRAPHY

Reducing perspective distortion

Use of

a shift lens

Reduce perspective

Elevate camera by use of adjacent

building or crane

May be challenging keeping

camera perpendicular to building

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MODULE 4: SCALERECT-PHOTO


Digital Survey > SANTANADimensional> indirect (photographic)

Scaled - Rectifiedphotography

• How to reduceperspective

– Same rules apply to horizontal perspective

– Use manual exposure when producing a

mosaic

Slide courtesy of Christian Ouimet, Public Works Canada


Digital Survey > SANTANADimensional> indirect (photographic)

Scaled - Rectifiedphotography

Slide courtesy of Christian Ouimet, Public Works Canada


KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA

IMAGE ISSUES

Radial distortion is a failure of a lens to be rectilinear: a failure to image lines into lines. If a photograph is not

taken straight-on then, even with a perfect rectilinear lens, rectangles will appear as trapezoids: lines are imaged as

lines, but the angles between them are not preserved (tilt is not a conformal map). This e ect can be controlled by

using a perspective control lens, or corrected in posprocessing

Issues:

Perspective distortion is a warping or transfor-

mation of an object and its surrounding area that

di ers signi cantly from what the object would

look like with a normal focal length. Perspective

distortion can typically be seen in images shot

using a wide angle of view, where an object close

to the lens appears abnormally large relative to

more distant objects, or in distant shots with a

narrow angle of view, where the viewer cannot

discern relative distances between distant

objects and more distant objects may look

exceptionally large, when such images are

http://en.wikipedia.org/wiki/Distortion_(optics) - http://en.wikipedia.org/wiki/Perspective_distortion_(photography)

http://www.dxo.com/us/photo/dxo_optics_pro/optics_geometry_corrections/distortion

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MODULE 4: SCALERECT-PHOTO


KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA

LENS DISTORTION

For appropriate products in recti ed photography, lens distortion should be minimized. There are two

main types of lens distortion: radial and tangential distortion. Since the amount of tangential distortion is

neglible for simple recti cation procedures, this procedure only concentrate on removing radial distortion

Image with radial distortion

Image without radial distortion

Radial distortion coe cients should be identi ed during calibration process

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MODULE 4: SCALERECT-PHOTO


KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA

CAMERA CALIBRATION USING 2D PATTERNS

Distance of squares (ex. 29 cm)

Distance of squares (ex. 29 cm)

Number of squares

between 1 and 2 (ex. 11)

1

2

Number of squares

between 1 and 4 (ex. 7))

3

4

CAMERA POSITION

CAMERA POSITION

CAMERA POSITION

CAMERA POSITION

CAMERA POSITION

CAMERA POSITION

CAMERA POSITION

CAMERA POSITION

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MODULE 4: SCALERECT-PHOTO


KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA

SCALE RECTIFY PHOTOGRAPHY AND CAD OVERLAY

A CAD package is used

to overlay the geometry

of the feature

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MODULE 4: SCALERECT-PHOTO


SCALE RECTIFY PHOTOGRAPHY AND CAD OVERLAY SANTANA

  • D the distance to the object (in mm)

  • f the equivalent 35mm camera focal length (in mm)

  • N the total number of pixels of the taken photograph.

  •  f the equivalent 35mm camera focal length (in mm)  http://www.dpreview.com/reviews/specs.asp


SCALE RECTIFY PHOTOGRAPHY AND CAD OVERLAY SANTANA

  • Example

  • Canon Eos 400d (sensor size of 22,2 x 14,8 mm)

  • image from a distance of 10 meter

  • Using the full 10 MP

  • focal length of 28mm

  • Convert Focal length to 35mm equivalent

    • For most cameras this can be done by multiplying the focal length by 36 and then dividing the result by the width of the sensor.

  • Put everything into formula

  • RESULT : 1 pixel = 1,274 mm in reality


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