introduction on photogrammetry - cenn

1 Koert Sijmons

Introduction on Photogrammetry

By: Koert Sijmons

3 Koert Sijmons

Topographic map Aerial photograph

4 Koert Sijmons

Difference between map and photo

MAP

PHOTOGRAPH

Orthogonal projection.

Central perspective projection

Uniform scale. Variable scales.

Terrain relief without

distortion (contour

lines).

Relief displacement in the image

All objects are represented

also the non visible

Only objects that are

visible.

An abstract representation Is a real representation

of the earth surface, no legend needed.

Cont.

5 Koert Sijmons

Difference between map and photo

Cont.

Representation geometrically

correct

Representation geometrically

not correct

Elements appear

displaced in its real

position and in different

shapes, due to the generalization

process.

Objects appear displaced due to

geometric distortions.

MAP

PHOTOGRAPH

6 Koert Sijmons

Basic principles of Photogrammetry

Photogrammetry is the science and technology of obtaining

spatial measurements and other geometrically reliable derived

products from photographs.

Obtaining approximate distances, areas, and elevations using

hardcopy photographic products with unsophisticated equipment

Photogrammetric analysis procedures can range from:

Geometric concepts to generating precise digital elevation

Models (DEMs), Orthophotos,and thematic GIS data

Cont.

7 Koert Sijmons

Introduction

The terms digital and softcopy photogrammetry are inter-

changeable to refer to any photogrammetric operation

involving the use of digital raster photographic image data

rather than hardcopy images.

Digital photogrammetry is changing rapidly and forms the

basis for most current photogrammetric operations.

However, the same basic geometry principles apply to

traditional hardcopy (analog) and softcopy (digital )

procedures.

Cont.

8 Koert Sijmons

Introduction

Mapping from aerial photographs can take on numerous forms

and can employ either hardcopy or softcopy approaches.

Traditionally, topographic maps have been produced from

hardcopy stereo-pairs in a stereo-plotter device.

A stereo-plotter is designed to transfer map information

without distortions, from stereo photographs.

A similar device can be used to transfer image information,

with distortions removed, in the form of an Orthophoto.

Cont.

9 Koert Sijmons

Introduction

Orthophotos combine the geometric utility of a map with the

extra “real-world image” information provided by a photograph.

The process of creating an Orthophoto depends on the

existence of a reliable DEM for the area being mapped.

The DEM is usually prepared photogrammetrically as well.

A digital photogrammetric workstation generally provide the

Integrated functionality for such tasks as generating:

DEMs, digital Orthophotos, perspective views, and

“fly-throughs” simulations, as well as the extraction of

spatially referenced GIS data in two or three dimensions

10 Koert Sijmons

Introduction

11 Koert Sijmons

60% forward overlap 20 - 30% side lap

Flight strip 1

Flight strip 2

12 Koert Sijmons

Terrain

1

1

2

2

3

3

4

4

5

5

6

6

Flight line

Nadir line

(ground trace of aircraft)

Endlap

Photographic coverage along a flight strip

Conditions during exposures

Resulting photography

13 Koert Sijmons

Flight line 1

Flight line 2

Flight line 3

Exposure station

Flight paths (Photo run)

14 Koert Sijmons

Focal length

Focal length

E

O

Exposure station (L)

Negative

d

a b

c

e

y

x

o Positive

c’ d’

b’

a’

C

D

A

B

e’ o’

Optical axis

Geometric elements of an aerial photo

15 Koert Sijmons

Eustasius

June 1982

2205

Fiducial marks

Message Pad Watch Altimeter

Principle point

16 Koert Sijmons

Photography

central projection

17 Koert Sijmons

Central perspective

19 Koert Sijmons

L

Principle

Point

Photo Map

Orthogonal projection Central Perspective projection

Geometry of Map and Photo

Varied scale

Relief displacement

Result in:

Different size, shape and

location of static objects

20 Koert Sijmons

Scale at sea level (0 mtr.):

Scale at 50 mtr. Terrain elevation:

Scale at top volcano (590 mtr.)

0

50

590

S = scale

f = focal length (15.323 cm)

H = flying height (6200 mtr.)

h = local terrain height

1:40.462

1:40.136

1:36.612

Closer to the camera = larger scale

Scale S = H – h

f

21 Koert Sijmons

Positive f

o

h

L

H

O A

A

”

A’

a a’

D

d r

Relief displacement Occurs for terrain points

Whose elevation is above

or below the reference

Elevation (at O).

Can be used for height

Calculation (h):

h = d H

r

d = 2.01 mm.

H (Flying Height) = 1220 mtr.

r = 56.43 mm.

h = 43.45 mtr.

22 Koert Sijmons

23 Koert Sijmons

o’ o

Change in positions of

stationary objects caused by a

change in viewing position

Parallax of point A

Pa = xa – x’a

DATUM

y

x

L

y’

x’

L’

a b a’ b’

x’ a

o

x a b a

o’

A

B

o’

a’ b’

o

Pa = the parallax of point A

x = The measured x coordinate

of image a on the left photo a

x’ = the x coordinate of image a’

on the right photo a

24 Koert Sijmons

Y

X

Y

Y

X

O X

Y

X

O’

a b a’ b’

x a x’ a

Pa = x – x’ a a

Pa = 54.61 – (- 59.45) = 114.06 mm

x b

x’ b

Pb = x – x’ b b

Pb = 98.67 – (- 27.39) = 126.06 mm

ΔP = 12.00

25 Koert Sijmons

H

O

o

O’

A

f

O A

Y A

A x X A

h A

L’

o’

f

B = Air base H = Flying height f = Focal length Pa B

f H - h A

= __ _____ Pa = parallax of point A h = Height above datum

A

H – h = Bf

P a

____

A

Also from similar triangles:

LOA A x

and Loa x

H - h A

X A _____ a x

= __

f

From which:

L

x a

a x

a y a a’

a’ x

x’ a

X A

x (H – h ) a A

= _________

f

X A

= B

x a

p a

____

Y A = B y a

p a

____

26 Koert Sijmons

X A

= B

x a

p a

____ Y A = B

y a

p a

____ Parallax equations

are ground coordinates of a point with respect to an arbitrary

coordinate system whose origin is vertically below the left

exposure station and with positive X in the direction of flight

X and Y

p Is the parallax of the point in question

x and y are the photocoordinates of point a on the left-hand photo

The major assumptions made in the derivation of these

equations are that the photos are truly vertical and that they

are taken from the same flying height.

27 Koert Sijmons

Aerial Photo Concept

Digital Orthophotos are generated from the same type of

Aerial photo as conventional hardcopy Orthophotography.

The difference lies in the scanning of the airphoto, converting

the photo to a digital image product that will be manipulated

and processed with a computer.

Cont.

28 Koert Sijmons

Aerial Photo Concepts

The relationship between photo scale, scanning resolution

and final scale must be considered.

Final resolution of the Orthophoto product is based on the

application that the Orthophotos are being used for, and also

the limitations of disk space that may be encountered during

the project.

It is not always beneficial to scan an airphoto at the highest

number of dots per inch (DPI), if the application does not

warrant such high resolution.

Cont.

29 Koert Sijmons

Aerial Photo Concepts

A simple equation can be used to calculate the scanning

resolution necessary based on the original scale, final

output pixel size and the size of the hardcopy photo.

The equation is: where:

p = output pixel size (cm)

W = photo size (cm)

r s = scanning resolution (DPI)

d = Foot print size (cm)

Cont.

= ______ r s W p *

d

* 2,54 cm/inch

30 Koert Sijmons

Aerial Photo Concepts

Example:

A photo is 9 inches (22.86 cm) across, and covers a ground

distance of 8 Km. The final resolution required is 3 meter

the scanning resolution in dots per inch (DPI) would be:

r s =

800000 cm

* 2.54 cm/inch = 296 DPI 22.86 cm * 300 cm

_________________

Cont.

31 Koert Sijmons

Aerial Photo Concepts

The scanning resolution can also be determinated from

the photo scale, without having calculate the ground distance.

photo scale is more commonly quoted in the aerial survey

report.

= ______ r s W p *

d From the previous mentioned equation:

we derive:

r s =

d

W * S * 2.54

p

____ ___ = 2.54 ____

p

where S = photo scale Cont.

32 Koert Sijmons

Aerial Photo Concepts

For example, a typical aerial survey might consist of photos

at 1:4,800 scale. The desired output resolution for the

orthophotos is approx. 30 cm. For 22.86 cm airphoto,

a reasonable scanning resolution would be:

r s =

_____ * * S

2.54 2.54

p = 4800

_____

30 = 406 DPI

33 Koert Sijmons

Aerial Photo Concepts

The St. Eustasius demonstration dataset was flown at an

average photoscale of 1:40,500

The photos are 22.86 cm x 22.86 cm.

We want a ground resolution of 3m., so we must calculate the

scanning resolution.

r s = S * *

2.54

p = 40.500

300 = 342.9 DPI ____ 2.54 ____

34 Koert Sijmons

Photogrammetric Triangulation

What is it?

- Increasing the density of whatever ground control you have;

called “Control Point Extension”

What does it do?

- Computes coordinate values for any point measured on two

or more images (tie points)

- Computes positions and orientation for each camera station

Cont.

35 Koert Sijmons

Photogrammetric Triangulation

Computes position of

Each camera station

- X,Y and Z (where Z is

flying height)

- Omega ()

- Phi ()

- Kappa ()

36 Koert Sijmons

f

Aerial photographs f Deformations

X

Y

Z

X

Y

Z

X

Y

Z

37 Koert Sijmons

Photogrammetric Triangulation

How do you do it?

Interior Orientation

Exterior Orientation

Image measurements

Ground Control Points (GCP)

38 Koert Sijmons

Interior Orientation

- Lens focal length

- Origin of co-ordinate system (principal point)

- Radial lens distortion

Objective: Interior Orientation models the geometry inside the camera

Coordinate systems

- Establish the relationship between positions in the image

(pixel) and the corresponding position in the camera (mm.)

The coordinates of the fuducial points in the camera are

known.

39 Koert Sijmons

left right

Principle point Principle point

Aerial photographs en stereo

40 Koert Sijmons

Fiducial marks

Interior Orientation: Image used

during demonstration

Principle point

Image details:

Average photo scale:

Scanning resolution:

Ground resolution per pixel:

1:40,500

300 DPI

(2.54 / 300)*405 =

3.43 m.

41 Koert Sijmons

Interior Orientation

Film: coordinate position are measured in

microns (Image coordinate system)

Digital image: coordinates positions are

measured in pixels (Pixel coordinate system)

Using fiducial points a linear relationship can

be established between film and image

coordinate postions

42 Koert Sijmons

1: 106.004

2: -105.999

3: -106.004

4: 106.002

X and Y coordenates of

the fuducial points

-106.008

-105.998

106.005

106.002

-X

1 2

3 4

Principal point

43 Koert Sijmons

Column

X

Y

Relation between

Pixel coordinates

(Line,Column)

and

Image coordinates

(in the camera in millimeters)

(x,y)

44 Koert Sijmons

0

Col pixel 0

Lin pixel 0

A

Col pixel A

Lin pixel A

Pixel coordinate system

Image coordinate system (film)

Colum 0,0

45 Koert Sijmons

Interior Orientation

- Camera calibration information - Obtained from “camera calibration certificate”

- Calibration elements:

- Focal Length

- Fiducial coordinates

- Principal point location

- Radial lens distortion

46 Koert Sijmons

Exterior Orientation

Objective: Establishing a relationship between the digital image

(pixel) co-ordinate system and the real world (latitude and longitude)

co-ordinate system

Ground Control Points

Visually identifiable

Preferably on multiple images

Larger image blocks need less control per image

Need to be well distributed in X,Y and Z

Ground control types:

– Full (X,Y,Z)

– Horizontal (X,Y)

– Vertical (Z)

47 Koert Sijmons

O: Projection centre

A: Point on the ground

a: Image of A on the

photograph

from similar triangles:

O (Uo, Vo, Wo)

colinearity condition

a (Ua, Va, Wa)

A (UA, VA, WA)

oa

oa

oa

a

oA

oA

oA

a

oa

oA

oa

oA

oa

oA

WW

VV

UU

s

WW

VV

UU

:or

sWW

WW

VV

VV

UU

UU

UA -Uo

Ua -Uo

Wo -Wa

Wo -WA

48 Koert Sijmons

angles

Z

(Kappa)

X (Omega)

Y (Phi)

49 Koert Sijmons

What do these letters mean?

Position of a point in the image: x, y

Position of the corresponding terrain point: U, V, W

Known after interior orientation: xPP, yPP , c

From Exterior orientation: Uo, Vo , Wo,

r11, r12, r13, r21, r22, r23, r31, r32, r33 (computed from of , , )

For each point in the terrain its position in the image

can be computed from these two equations. (Different

for the left and the right image.)

PP

o33o32o31

o23o22o21

PP

o33o32o31

o13o12o11

y)WW(r)VV(r)UU(r

)WW(r)VV(r)UU(rcy

x)WW(r)VV(r)UU(r

)WW(r)VV(r)UU(rcx

50 Koert Sijmons

Resampling one pixel

Center of the orthophoto-

pixel in the original image

“Nearest neighbour”:

the value of this pixel

“Bilinear”: interpolated

between these 4

pixelcenters

51 Koert Sijmons

Example St Eustatius: How to accurately

transfer interpretation from photo to map!!!

Shoreline from topographical map Aerial photo

?

52 Koert Sijmons

Available: 2 digital stereo Aerial Photos at scale 1:40,000

of the Island of Sint Eustasius (Caribbean Sea)

Left Right

53 Koert Sijmons

Available: Topographic map at

scale:1:10,000 of St. Eustasius

54 Koert Sijmons

55 Koert Sijmons

Software: ERDAS IMAGINE 8.6

57 Koert Sijmons

Create New Block File

Working Directory

Type: Block File name

Sint_eustasius.blk

58 Koert Sijmons

Setup of Geometric Model

Frame Camera

59 Koert Sijmons

Select Projection

Set Projection

60 Koert Sijmons

Select Projection

UTM Zone 20 (Range 66W-60W)

61 Koert Sijmons

Select Spheroid Name

62 Koert Sijmons

63 Koert Sijmons

Set Horizontal/Vertical Units in:

Meters

64 Koert Sijmons

Set Fly Height in meters

V 6200

65 Koert Sijmons

Loading images

Load left and right images

From your working directory

66 Koert Sijmons

Loading Left and Right image

d:/het mooie eiland st eustasius/left img

d:/het mooie eiland st eustasius/right img

67 Koert Sijmons

Set up for Interior Orientation

68 Koert Sijmons

Set Focal Length

69 Koert Sijmons

Type: 4

70 Koert Sijmons

Indicating: left.img

Interior orientation for left image

71 Koert Sijmons

Load left image

1st Fiducial point Jumps automatically to next fiducial point

72 Koert Sijmons

2753.202 2655.394

1st fiducial point

Set fiducial mark

Coordinades 1st. Fiducial point

75 Koert Sijmons

Measure 2nd fiducial point, as

done for point 1

76 Koert Sijmons

Measure 3rd fiducial point, as

done for point 1 and 2

77 Koert Sijmons

Measure 4th fiducial point, as

done for point 1, 2 and 3

78 Koert Sijmons

Should be less than 1 pixel

All 4 fiducial points are measured

79 Koert Sijmons

Make adjustments for the fiducial points in

order to get less than 1 pixel RMSE

80 Koert Sijmons

Green infill indicates, that Interior orientation

has been carried out for left.image

81 Koert Sijmons

Indicating: left.img Indicating: right.img

82 Koert Sijmons

Interior Orientation for right image

83 Koert Sijmons

Measure the 4 fiducial points for the

Right image, starting with point 1,as

done for the Left image

84 Koert Sijmons

The measurement for the 4 fudical points

are completed with less then 1 pixel RMSE

85 Koert Sijmons

Both images have their interior

orientation (green)

Set Ground Control

Points (GCPs)

86 Koert Sijmons

2

3

4

5

6

7 8

9

10 11

12

13

14

15 16

17

1

Control Points

X = 502865

Y = 1932070

Z = 107 m.

Coordinates:

1

87 Koert Sijmons

1 1

Control Point in map with corresponding point in left image

88 Koert Sijmons

32 1931430 502400 7

20 1935180 502265 6

55 1933750 503780 5

45 1932060 502135 4

52 1933430 502775 3

23 1932850 501610 2

107 1932070 502865 1

Z Value Y Coordinates X Coordinates Pnt nr.

89 Koert Sijmons

0 1936998 502450 14

0 1934460 503515 13

20 1931880 506030 12

35 1930600 504340 11

10 1930820 505190 10

62 1933420 505250 9

46 1930760 503260 8

Z value Y coord. X coord. Pnt. Nr.

90 Koert Sijmons

0 1934310 500570 17

0 1937315 500730 16

0 1936998 501480 15

Z value Y coord. X coord. Pnt. Nr.

91 Koert Sijmons

Measuring Ground Control Points

(GCP’s)

Set Ground Control

Points (GCPs)

92 Koert Sijmons

93 Koert Sijmons

Add 1st. Ground

Control Point (GCP)

94 Koert Sijmons

1

1 Set register mark to point 1 in the right

image, according to the position of the

Ground Control Point in the map

1

1

Set register mark to point 1 in the left image,

according to the position of the Ground

Control Point in the map

502865.000 1932070.000 107.000

Register Ground

Control Point

Type in: X-coordinates: 502865.000

Y-coordinates: 1932070.000

Z-value: 107.000

for Point 1 Click: Enter

Register Ground

Control Point

95 Koert Sijmons

2

2

2

2

Set register mark to point 2 in the right

image, according to the position of the

control point in the map

Set register mark to point 2 in the left image,

according to the position of the control point

in the map

501610.000 1932850.000 23.000

Register Ground

Control Point

Register Ground

Control Point

Type in: X-coordinates: 501610.000

Y-coordinates: 1932850.000

Z-value: 23.000

for Point 2 Click: Enter

96 Koert Sijmons

3

3

3

3

Set register mark to point 3 in the right

image, according to the position of the

control point in the map

Set register mark to point 3 in the left image,

according to the position of the control point

in the map

502775.000 1933430.000 52.000

Type in: X-coordinates: 502775.000

Y-coordinates: 1933430.000

Z-value: 52.000

for Point 3 Click: Enter

Register Ground

Control Point

Register Ground

Control Point

97 Koert Sijmons

4

4

Set register mark to point 4 in the left image,

according to the position of the control point

in the map

Automatically display the

Image positions of Control

Points on the overlap areas

of 2 images. This capability

Is enabled when 3 or more

Control Points have been

measured

4

4

Set register mark to point 4 in the right

image, according to the position of the

control point in the map

Type in: X-coordinates: 502135.000

Y-coordinates: 1932060.000

Z-value: 45.000

for Point 4 Click: Enter

502135.000 1932060.000 45.000

Register Ground

Control Point

Register Ground

Control Point

98 Koert Sijmons

Continue the same

Procedure for the Remaining Ground

Control Points according to map and

Coordinate list

99 Koert Sijmons

Click right button Click right button

Control

Full

Change type “none” into “Full”

and

Change “Usage” into “Control

For all GCP’s

10

0

Koert Sijmons

Click: the automatic Tie

Point Collection Properties

icon

10

1

Koert Sijmons

50

Check to confirm that the

Image Layer Used for

Computation is set to 1

Check to confirm that the

Initial Type radio button is

set to Exterior/Header/GCP

Check to confirm that the

Keep All Points

checkbox is off (unchecked)

Click in the Intended Number

of Points Per Image field and

type: 50, then press Enter

Click the Run button

1

Check to confirm that the

Image Used radio button is

set to All available

10

2

Koert Sijmons

Click in the > column of

Point Ids to see where tie points

were placed. Tie points outside

the land area have to be deleted.

If the tie points needs to be

Adjusted, click the Select Point

icon and adjusted it in the

Detail View

Save Close

Activate Point

48

10

3

Koert Sijmons

Triangulation Properties

10

4

Koert Sijmons

10

5

Koert Sijmons

10

6

Koert Sijmons

The X and Y deviations of the

Coordinates are within the tolerance

of 1 pixel.

The image was scanned with a Ground

Resolution of 3 meter

The height value accuracy is

Within 0.64 meter

Save as…

10

7

Koert Sijmons

ASCII Text File (*.txt))

St_Eustasius

10

8

Koert Sijmons

Exterior orientation

has been completed

10

9

Koert Sijmons

Delete Tie Points with

negative height values Activate Point

45, 46, 47

After Triangulation all

Tie Points have

X, Y, Z References

11

0

Koert Sijmons

DTM Extraction

11

1

Koert Sijmons

Select:

Single DTM Mosaic

File Chooser

11

2

Koert Sijmons

DTM_ St.Eustasius

OK

11

3

Koert Sijmons

DTM_ St. Eustasius

30.000000 30.000000

Type: 30 meters V

Make Pixels square

11

4

Koert Sijmons

DTM processing

11

5

Koert Sijmons

DEM is calculated

Save…

11

6

Koert Sijmons

dem_st. eustasius

OK

11

7

Koert Sijmons

11

8

Koert Sijmons

Orthophoto generating

11

9

Koert Sijmons

Orthophoto Resampling

DEM

3.000000 3.000000

DEM.IMG

12

0

Koert Sijmons

Orthophoto generated

12

1

Koert Sijmons

Orthophoto

12

2

Koert Sijmons

DEM Orthophoto

12

3

Koert Sijmons

Topographic map Orthophoto

12

4

Koert Sijmons

12

5

Koert Sijmons

12

6

Koert Sijmons

12

7

Koert Sijmons

12

8

Koert Sijmons

12

9

Koert Sijmons