photogrammetry.pptx

 Advance Surveying
Aerial Photogrammetry

Lecture Outline
 Definition
 Objectives
 Classification: quantitative and qualitative
photogrammetryApplication
 Comparison of map and aerial photograph
 Vertical, Tilted and Oblique photograph

 Definition ofAerial Photogrammetry:
Aerial Photogrammetry is advance technique of
obtaining the information about object or area
without coming into the physical contact with the
object or area under investigation.
Photo=Picture
Grammetry =Measurement
Photogrammetry= Photo-measurement

 Objectives:
• To prepare the maps
• To make the reconnaissance survey
• To collect the military intelligence
• To interpret the geology and soil data
• To make survey of remote area
• To make survey of buildings
• To conduct environmental assessment
• To conduct Power line inspection
• To conduct forest survey
• Movie production

 Classification:
Sr. No. Terrestrial photogrammetry Aerial photogrammetry
1
2 Photographs are taken by photo
theodolite mounted at stationary
and elevated position.
Cameras fit to an aeroplane that flies
take pictures
3 Terrestrial photogrammetry
comparatively needs much less
investment and technical skill to
carry out.
Aerial photogrammetry requires a
high-end infra support:
4 To map a small piece of land. To map a large piece of land.
5 Maps are compiled from the
photographs
Accessories required for
interpretation & plotting the maps

 Comparison of map and aerial photograph:
Sr. No. Map Aerial photogrammetry
1
2 It is an orthogonal Projection. It is a central Projection
3 Amap is a geometrically correct. An aerial photograph is a geometrically
incorrect.
4 The scale of the map is uniform The scale of the photograph is not
uniform
5 Enlargement/reduction of the maps
involves redrawing it
Enlargement/reduction does not change
the contents of the photographs
6 Map reading is common and more
familiar to users
Photograph needs a special technique to
read the photo-views
7 Plotting of map is economical Plotting of map is uneconomical
8 Map Prepared by conventional
method
Aerial Photograph preparation is highly
skill job
9 Time consuming method Time saving method

 Types of Photographs: Vertical , Tilted & Oblique
Types of aerial photographs on the basis of orientation of
camera axis:
• Vertical photograph: An aerial photograph taken with the camera
axis/optical axis coinciding with the vertical to the ground is known as
vertical photograph.
• Tilted photograph: An aerial photograph in which the camera axis is
unintentionally tilted by small amount (less than 3 °) from
vertical/perpendicular to the ground is known as tilted photograph.

• Oblique photograph:
An aerial photograph taken keeping the camera axis intentionally tilted from
the vertical is known as oblique aerial photograph. The amount of tilt ranges
from 30° to 60 °. The advantage of oblique photographs is that they cover
large area and they also provide side view of features.
Oblique photographs are of two types –
Low oblique: Oblique photographs in which horizon is not seen. Tilt is 30°.
High oblique: Oblique photographs in which horizon is seen. Tilt is 30° to 60°.

Vertical Aerial
Photograph
Image ID
Clock
Fiducial mark
defining the
frame of
reference for
spatial
measurements
Level bubble
Altimeter
Frame No.
Vertical photo taken from with a 230 x 230-mm precision
mapping film camera showing Langenburg, Germany

Geometric Characteristics: Photo
Scale
Scale of Arial Photographs (Photographic Scale)
 The scale of a photograph expresses the mathematical relationship
between a distance measured on the photo and the corresponding
distance measured on the ground.
 A photograph scale is an expression that states one unit of distance
on a photograph represents a specific number of units of actual
ground distance.
 Scales may be expressed as unit equivalents (1 mm = 25 m),
representative fractions (1/25,000) or ratios (1: 25,000).
 Unlike maps, which have a constant scale throughout, the aerial
photographs have a range of scales that vary in proportion to the
elevation of the terrain involved.
 The most straight forward method for determining photo scale is to
measure the corresponding photo and ground distances between
any two points. The scale S is then computed as the ratio of the
photo distance d to the ground distance D.
 S = photo scale = photo distance/ground distance = d/D

Aerial Photo
Scale
The scale of a photograph is
determined by the focal length of the
camera and the vertical height of the
lens above the ground.
The focal length (f) of the camera is
the distance measured from the
centre of the camera lens to the film.
The vertical height of the lens above
the ground (H-h) is the height of the
lens above sea level (H), minus the
height of the ground above see level
(h), when the optical axis is vertical
and the ground is flat.
These parameters are related by
formula
S = f / (H – h)

Geometric Characteristics:
Scale
 Photographic Scale Contd.
 For instance, if the photo scale were 1:63,360,, then 1
inch on the photo would represent 63,360 inches. The
first number (map distance) is always 1. The second
number (ground distance) is different for each scale;
the larger the second number is, the smaller the scale
of the map. i.e. Large is Small.
 Quite often the terms large scale and small scale are
confusing to those whose who are not working with scale
expression on a routine basis.
 A convenient way to make scale comparisons is to
remember that the same objects are smaller on a smaller
scale photograph than on a larger scale photo.
 A large scale photograph will provide a detailed and high
resolution view of a small area.

Large Scale Vs. Small Scale
A map’s scale determines how a feature will be
represented. On a large-scale map, a river might be
represented as a polygon rather than a line or a
city’s extent is so large that it can only be accurately
represented as a polygon rather than a point.
Scale can be used as a
measure of viewable
detail; small scale
implies less detail is
visible, large scale
implies more detail is
visible. Thus, in GIS
scale can be used to
control display; as scale
increases (becomes
larger and more
“zoomed in”) more
detail can be displayed
without overcrowding
the screen display.

Comparative Geometry of a Map and a
Vertical Photograph
• On a map we see a top view of
objects in their true relative
horizontal positions. On a
photograph, areas of terrain at
the higher elevations lie closer
to the camera and therefore
appear larger than the
corresponding areas lying at
lower elevations.
• The image of the tops of objects
appearing in a photograph are
displaced from the images of
their bases. This distortion is
known as relief displacement
and causes any object standing
above the terrain to lean away
from the principal point of a
photo radially.

SCALE OF PHOTOGRAPH
►To perform computations, one must know:
▪ H = height above datum from which photos
taken.
▪ f = focal length of camera lens – in cm or mm

Scale of a Vertical Photographs
► f = focal length 6” or 152.4 mm is common
f = focal length 6” or 152.4 mm is common
► H’ = height of plane above ground
► h = height (elevation) of ground
► H = height of place above datum
► S = f or
H
’
f
H-
h

Scale varies from point to point
►Scale of photograph at point P on ground
having elevation hp
►Scale for any point = s
►Representative fraction (R.F.) =

Scale of a Vertical Photo
► Average Scale = All the points of photograph
are asumed to be having average elevation above
m.s.l.
SAV. =
► Datum Scale = All the points of photograph are
asumed to be projected on M.S.L. (R.L.± 0.00)
SD= f
H
f
H-hav.

Other methods of finding scale of
vertical photograph
► By measuring Ground distance
►
►
►
By determining the distance from existing
map
= Photo distance
= distance on existing map

Displacement and errors
►In photography survey we try to represent 3-
D surface of earth as 2D image.
►Object appears in photographs are
geometrically distorted. / ( known as relief
displacement)
► Reasons for Distortions
▪ Perspective view
▪ Movement of camera
▪ Instability of aircraft
▪ Variation in altitude , tilt and speed
▪ Curvature of earth
▪ Rotation of Earth

Ground control survey
►Purpose: Determine exact position of aerial
camera at the instant of exposure and
identify the objects on ground.
►Steps
►Targets (signals) are placed on ground.
►Targets are surveyed by Triangulation
►Ground control ( Triangulation, B.M.
Azimuth,)and photo control ( position of
signal and elevation)
►Horizontal control ( Triangulation)and
Vertical control ( leveling)

Procedure for Aerial survey ( Flight
planning)
►Parameters
▪ Altitude of flight (H)
▪ Focal length of camera (f)
▪ Size of photograph
▪ Size of area or land to be photographed
▪ Alignment of flight line and parallel flight line
▪ Lateral overlap
▪ No of photo in each flight line and overlap
▪ Scale of flight map.
▪ Ground speed of aeroplane
▪ Time interval of successive photographs

Photomaps and Mosaics
►Used as alternate of maps
►Photomap is single photograph
►Two or more photograph combined is known
as mosaic.
►In mosaics objects are easily recognized.
►In maps symbols of objects are used
►In mosaics true picture of objects helps
►Cost and time saves in mosaics preparing
►Mosaics can be used by non technical person

Procedure to prepare Photo
mosaics
►Manual
▪ Zerox procedure
►Digital
▪ Photo editing software

Principle of stereoscope
►Two separate photo viewed in stereoscope
the image of left photograph viewed by left
eye and the image of right photograph
viewed by right eye is fused together in
brain to provide 3- dimensional view. This is
called stereoscopic fusion

Stereoscopic View
One of the advantage of all
aerial photographs is that when
taken as overlapping pairs
(called stereopairs) they can
provide a 3D view of the terrain
(also called perspective view).
The 3D view is made possible
by the effect of parallax.
Parallax refers to the apparent
change in relative positions of
stationery objects caused by a
change in viewing position.
Our left and right eyes are
recording information from two
slightly differing viewpoints; the
brain uses the effect of parallax
to give us the perception of
depth.

Viewing Photos Stereoscopically
Paracutin volcano in Mexico.
(Source: Curran, 1988)
Stereopairs: overlapping vertical photos

Stereoscopes
Pocket Stereoscope Mirror Stereoscope
Scanning Stereoscope ‘Interpreterscope’ (Carl Zeiss)

Parallax in Aerial Stereoscopic View
►In normal binocular vision the apprent
movement of a point viewed first with one
eye and then with the other is known as
Parallax.
►Parallax is displacement of two images in
successive photographs.

photogrammetry.pptx

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