sug541 - advanced photogrammetry - 17 questions

MARA UNIVERSITY OF TECHNOLOGY BACHELOR OF GEOMATIC AND SURVEYING SCIENCE (AP220) Jack Ruzaini ([email protected]) ADVANCED PHOTOGRAMMETRY (SUG541) ASSIGNMENT 1 _________________________________________________________________________________________________________

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QUESTION 1

What is Photo Scale?

1. Photo scale is the ratio of a distance on the photo to the corresponding distance on the ground.

2. Photo scale may be presented as unit equivalents, unit fractions, dimensionless representative

fractions or dimensionless ratio.

3. Photo scale is shown as where one unit on the photograph represents a specific number of the

same units on the ground. For example, a photo scale of 1 : 15 000 means 1 mm unit on the photo

is represents 15 000 mm or 15 metres unit on the ground.

4. Two common types of photo scale are:

i. Large Scale – means the larger ground features and more detailed in size. However the area of

ground coverage on the photo is less than at smaller scales.

ii. Small Scale – means the smaller ground features and less detailed size. However the area of

ground coverage on the photo is greater than at larger scales.

QUESTION 2

List out information that can be obtained from an aerial photograph.

1. Number of Photo

2. Flying Height

3. Time

4. Date

5. Scale

6. Number of Flight Line. Example, L1N means Line One Northing

7. Film Colour. Example, FC 1220

8. Focal Length

9. Type of Camera

10. Four (4) Fiducial Marks

MARA UNIVERSITY OF TECHNOLOGY BACHELOR OF GEOMATIC AND ADVANCED PHOTOGRAMMETRY_________________________________________________________________________________________________________

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QUESTION 3

If a distance of a line on the photograph is known as 1 c

ground if the photographic scale is 1 : 10 000

Distance of a line on the photograph 1 cm means 10 mm unit

Photo Scale 1 : 10 000 means 1 mm unit on the photo represents 10 000 mm or 10 m on the ground.

If the distance on the photograph is known as 10 mm, so the equivalent distance on the ground is 100

000 mm or 100 m on the ground.

QUESTION 4

How many fiducial marks you can see on an aerial photograph? Categorize them.

There are four (4) or eight (8) fiducial marks on an aerial photograph. And it falls into few categories:

1. Circle

2. Square

3. Rectangle

4. Diamond, etc

QUESTION 5

Define what is principal point.

1. Principal point is defined as a

photograph.

2. It is also the intersection point between lines that link the opposite fiducial marks

3. It is also the nadir of the optical axis of the camera during the instant of exposure.

MARA UNIVERSITY OF TECHNOLOGY BACHELOR OF GEOMATIC AND SURVEYING SCIENCE (AP220) Jack RuzainADVANCED PHOTOGRAMMETRY (SUG541)

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If a distance of a line on the photograph is known as 1 cm, what is it’s equivalent distance on the

ground if the photographic scale is 1 : 10 000

Distance of a line on the photograph 1 cm means 10 mm unit



000 mm or 100 m on the ground.


fiducial marks on an aerial photograph. And it falls into few categories:

rincipal point is defined as a point that lie on the focal plane and the geometric centre of

It is also the intersection point between lines that link the opposite fiducial marks

It is also the nadir of the optical axis of the camera during the instant of exposure.

ni ([email protected])

ASSIGNMENT 1 _________________________________________________________________________________________________________

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m, what is it’s equivalent distance on the




fiducial marks on an aerial photograph. And it falls into few categories:

lie on the focal plane and the geometric centre of

It is also the intersection point between lines that link the opposite fiducial marks.

It is also the nadir of the optical axis of the camera during the instant of exposure.


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QUESTION 6

What is the difference between principal distance and focal length of a camera?

1. Principal distance is the distance between two principal points and it is conjugate.

2. In theory the principal distance is seems same as the focal length. However principal distance

differs from focal length when the lens is focused at a closer distance, the principal distance

changes.

3. Instead the term used in the lab is “principal distance” but when in the field it is called “focal length”.

QUESTION 7

What is fiducial center? How it is determined?

Fiducial Center is the intersection of the diagonal lines connecting fiducial marks, which lie diametrically

apart.

Fiducial center also the origin of the coordinate x and y given in rectangular.


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QUESTION 8

What are the differences between a metric camera and a non – metric camera?

Metric Camera Non – Metric Camera

1. Been specifically designed for photogrammetric

purposes and take large format

photogrammetric images on stable-base film or

glass plates

2. A stable interior orientation, that is lens cone is

rigid and the focusing distance pre-set at the

factory. The optical axis is defined by fiducial

marks fixed to the camera which are

reproduced on each exposure as reference

points;

3. A low distortion lens whose characteristics

(focal length, radial lens distortions) are known

from a manufacturer’s calibration test

4. An image surface which is flat within a fine

tolerance and which incorporates a film

flattening device such as a pressure plate or

vacuum system.

1. An unstable interior orientation. The effective

focal length may change for each exposure

and the direction of the optical axis may alter

with focusing movements

2. A lack of fiducial marks

3. Irregular lens distortions. As well as radial lens

distortions, relatively large tangential

distortions may be present in the lenses of

older amateur camera.

4. An unsophisticated film flattening device. The

film may be buckled at the time of exposure,

but will be held flat whilst image coordinates

are read from it. the buckling may vary from

frame to frame and consequently is very

difficult to correct during calculations for object

coordinates

5. Small image format. The accuracy of

determining the position of an object by

photogrammetry is claimed to be directly

related to the area of the photographed image.

6. However the modern lenses available for

small format non-metric cameras often have a

better pictorial quality than the low distortion

and lower resolution lenses in metric cameras.


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QUESTION 9

Explain the Newton’s Lens Law. Show the expression.

1. Lens formula:

The relation between u, v and f is called lens formula. 1/f = 1/v – 1/u

2. Lens maker formula:

The relation focal length (f), refractive index (µ), radius of curvature of first and second (R1 & R2)

which refracting surfaces of a thin lens is known as lens maker formula.

1/f = (µ – 1) (1/R1 – 1/R2)

3. Newton Formula:

Newton’s formula measures the distance of object (x1) and (x2) from the first and second principal

foci not from the optical centre. then Newton's formula states f2 = x1x


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QUESTION 10

What is the differences between an oblique photograph and a panoramic photograph?

Oblique Photograph Panoramic Photograph

An oblique photograph is taken when the camera is

focused at any angle between three degrees from

vertical and the horizon.

There are two basic types of oblique photograph:

high-angle and low-angle. In high-angle oblique,

the apparent horizon is shown, while in low-angle

oblique the horizon is not.

With high oblique photograph, atmospheric haze

and clouds often prevent the viewer from seeing

the true horizon.

The furthest point viewable in high oblique aerial

photography is called the apparent horizon.

Panoramic photography is achieved by stitching a

number of photographs together to form a single

"Wide" shot.

Panoramic aerial photography can be done using

full-sized helicopters, their unmanned counterparts,

or pole cams.

Pole cams are good for very low altitudes but they

are limited to about 100 feet and road access is

needed.

Full-sized helicopters are the platform of choice for

high-altitude panoramas; however new

technologies permit unmanned helicopters, coupled

with advanced GPS autopilot stabilization systems,

to be positioned within a few feet from any

elevation or location.

This type of aerial photography is perfect for

showing views from proposed or under-

construction high-rise buildings.


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QUESTION 11

Show the equations of a photo scale for a vertical photo and an oblique photo.

Vertical Photograph Oblique / Tilted Photograph

1. Scale of Vertical Photograph Over Flat Terrain

S = ��

��

2. Scale of Vertical Photograph over Variable Terrain

(at a point)

S = ��

��

H = Flying Height, h = the elevation at point

3. Scale of Vertical Photograph by other method

S = ��

�� x map scale

S =

�

!"#�$%��&�#'(�$

)�*

f = focal length

y’ = calculated coordinate of the point in the auxiliary

system

H = Flying height above datum for the photo

h’ = elevation of certain object point above datum


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QUESTION 12

Define the followings:

i. Nadir Point

it is the point where a plumb line dropped from the front nodal point pierces the photograph. This

point is vertically beneath the exposure station.

ii. Pass Point

iii. Tie Point

iv. Control Point

A reference point precisely located on both the ground and the photo (ground control point) on both

a map and the photo (map control point), or on two adjacent photos (photo control point)


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QUESTION 13

What is Snell’s Law?

Snell's law (also known as the law of refraction) named after

Dutch mathematician Willebrord Snellius, one of its discoverers, is

a formula used to describe the relationship between the angles of

incidence and refraction, when referring to light or other waves

passing through a boundary between two different isotropic media,

such as water and glass.

The law says that the ratio of the sines of the angles of incidence

and of refraction is a constant that depends on the media.

In optics, the law is used in ray tracing to compute the angles of

incidence or refraction, and in experimental optics and gemology to

find the refractive index of a material.

Refraction of light at the interface between two media of

different refractive indices, with n2 > n1. Since the

velocity is lower in the second medium (v2 < v1), the

angle of refraction θ2 is less than the angle of incidence

θ1; that is, the ray in the higher-index medium is closer to

the normal.

Snell's law is also satisfied in the metamaterials which

allow light to be bent "backward" at a negative index,

with a negative angle of refraction.

Snell's law states that the ratio of the sines of the angles of incidence and refraction is equivalent to the

ratio of velocities in the two media, or equivalent to the opposite ratio of the indices of refraction:

v = velocity, SI units are m/s

n = refractive index, which is unitless

Snell's law follows from Fermat's principle of least time, which in turn follows from the propagation of light

as waves.


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QUESTION 14

What are the parameters of inner orientation?

1. Coordinate system.

2. Principal distance.

3. Focal length.

4. Principal point.

5. Fiducial mark coordinates.

QUESTION 15

What is relative orientation? How it differs from absolute orientation?

Absolute orientation includes the identification of ground control features and the measurement of the

corresponding image coordinates. Implementations of automatic absolute orientation are rare and work

under restricted conditions only. These measurements, in principle, make ground control information as

such, and thus also their identification in the images, obsolete. As it stands today, however, at least a

small number of control points are still needed to ensure a reliable solution.

In contrast to absolute orientation, relative orientation does not require the recognition of specific features.

The conjugate points used only have to be geometrically well distributed in the model area.

Relative orientation is a prerequisite in order to provide users from photogrammetry and other disciplines

with parallax-free stereo viewing for photogrammetric date collection, interpretation purposes, and a

number of other tasks.

Relative orientation is also the core for any automatic point transfer system. Moreover, the parameters of

relative orientation are

needed for epipolar

resampling of digital images.

Therefore, automatic relative

orientation is an essential

procedure for the automation

of further procedures in

photogrammetric stereo

processing.

“Relative orientation” is done by selecting correlative photo points: this eliminates model parallax.


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QUESTION 16

There are three (3) types of errors in photogrammetry. Discuss.

1. Gross Errors – mistakes or blunders caused by carelessness or negligence. E.g. point

misidentification, transcription error in recording a value, misreading of a scale.

2. Systematic Errors – is an error in measurement which follows some mathematical or physical law.

E.g. shrinkage or expansive of photograph, camera lens distortion, atmospheric refraction.

3. Random Errors – generally were small but can never be avoided entirely in measurement. E.g. in

estimating between least graduation of a scale.

sug541 - advanced photogrammetry - 17 questions

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