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Photogrammetry
VARUN SINGH
ASSISTANT PROFESSOR, CEDMNNIT ALLAHABADE-mail:[email protected],
mailto:[email protected]:[email protected]8/12/2019 Photogrammetry Lecture
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Introduction
Definition of Photogrammetry: the art, science, and
technology of obtaining information about physicalobjects and the environment by photographic and
electromagnetic images.
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Mapping from aerial photos is the best mapping procedure yet
developed for most large projects.
Used successfully for maps varying in scale from
1:1,000,000 to 1:120 with contour intervals as small as 3
meters.
Topographic mapping is the most common form. SOI
updated and done this way.
Used to reconstruct a scaled 3-dimensional optical model
of the lands surface using a stereoplotter.
Basic Information
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Basic Information (Contd..)
Uses: Aerial photos
Aid: geological investigations, soil surveys, landsurveys, tax mapping, reconnaissance andmilitary intelligence, urban and regionaldevelopment, transportation system
investigations, quantity estimates, shore erosion,etc.
Mathematical methods have been developed tomake precise 3-dimensional measurements from
photos. Phototriangulation: 3-dimensional positioning of survey
stations.
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Basic Information (Contd..)
Photogrammetry can not be used successfully over
the following types of terrain.
Desert or plains areas, sandy beaches, and snowthe
photograph as uniform shades with little texture.
Deep canyons or high buildings that conceal ground
surface.
Areas covered by dense forest.
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Basic Categories
Metrical photogrammetry obtaining measurements from
photos from which ground positions, elevations, distances,
areas, and volumes can be computed and topographic or
planimetric maps can be made
Photo interpretation evaluation of existing features in a
qualitative manner
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Types of Photogrammetry
Aerialseries of photographs of an area of terrain in
sequence using a precision camera.
Terrestrial photos taken from a fixed and usually
known position on or near the ground with the
camera axis horizontal or nearly so.
Close range camera close to object being
observed. Most often used when direct
measurement is impractical.
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History
The first use of photogrammetry was by Arago, aFrench geodesist, in 1840. This included
topographic and terrestrial.
The first aerial photogrammetry was by the French
in 1849 using kites and balloons. Laussedat (French)father of photogrammetry.
1st in N. America Deville, Surveyor General of
Canada.
SOI and GSI adopted photogrammetry as mapping
process
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History
Airplanes brought great change to photogrammetry. 1stused in 1913.
Used extensively in WWIphoto interpretation.
Used in WWIImapping for recon and intelligence.
WWII1960used often, expensive and accuracy
problems for engineering design. After mid 60sadvent of computer and plotting has
made photogrammetric mapping accurate andaffordable.
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Photogrammetry for Engineering
Defined: Photogrammetry is the process of
measuring images on a photograph.
Modern photogrammetry also uses radar imaging,
radiant electromagnetic energy detection and x-ray
imagingcalled remote sensing.
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Basic Categories of Photogrammetric Interpretation
Metrical Photogrammetry obtaining measurements fromphotos from which ground positions, elevations, distances,areas can be computed and topographic or planimetric mapscan be made.
Photo interpretation evaluation of existing features in aqualitative manner timber stands, water pollution, soils,
geological formations, crops, and military interpretation.
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Camera System
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Aerial Camera
A camera used for vertical aerial photography for mapping
purposes is called aerial survey camera.
At present there are only two major manufacturer of aerial survey
cameras
Leica-Helava System(LH System)- RC 30 cameraZ/I Imaging-(RMK-TOP) Camera
Modern aerial survey cameras produce negatives measuring23cmsx23cms(9 x 9in) Up to 600 photographs may be recorded in a
single film roll.
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Lens Cone
The most important and expensive single component within the camera is the
lens. This is interchangeable, and the manufacturers produce a range of cone,each of different focal length.
Focal Leng this the most important property of the lens since, together with the
flying height it determine the scale of the photograph. It also determines the angle
of view of the camera. The longer the focal length, the narrower the angle of view.
Lens are generally available in the following standard focal lengths.
Narrow angle (f=610mm)
Normal angle (f=305mm)
Wide angle (f=210,152mm)
Super wide angle (f=88mm)
The lens is responsible for projecting an optical image on to the film. In an
ideal lens all the light rays passing through one central point. Hence the
projection is called the Central Projectio n
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Camera classifications
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Camera Lens
Lens distortion anderrors cause the lightrays to deviate
IMAGE or EXPOSURE PLANE
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lens of high geometric quality
capable of exposing in rapid succession a large
no. of photographs while moving in an aircraft
at high speed
must have short cycling times, fast lenses andefficient shutters.
Single lens camera classified according to field of
view :
Normal angle camera
Wide angle camera
Super wide angle camera
Requirements of aerial mapping camera
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Types of Aerial Photography
Vertical Photographs:
This photograph is taken with the optical axis of the camera in truly
verticalor very nearly vertical (with tilt < 3o to 5o )
Tilt :
The angle formed between the optical axis of the camera
and a plumb line.
Types of photographs
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900
Lens
Film
VERTICAL
PHOTOGRAPH
Plumb Line
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Types of photographs
Oblique Photographs:
This photograph is taken with the optical axis of the camera
intentionally tilted at an angle >5o.Oblique photographs can be
categorized into
Low Oblique : These photos are tilted to such an angle so as notto allow the horizon to be seen on the photo.
( angle about 30o)
High Oblique: These photos are tilted at such an angle so as to
allow the horizon to be seen on the photo.
( angle about 60o)
Panoramic photograph
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30o
Plumb line
LOW OBLIQUE
PHOTOGRAPH
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HIGH OBLIQUE
PHOTOGRAPH
Plumb
line
Horizon
60o
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3/4/2014
sidelap endlap
STEREOSCOPIC COVERAGE
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Sensor Attitude/Orientation
Oblique
More Oblique
Vertical
2
3
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Camera System
Cameras used for air survey, as with all other survey
equipment, are precision-built, and their lenses are of suchhigh quality that aberrations are practically negligible
From the engineering point of view the most popular lens is
the wide-angle combined with a photograph format size of
230 mm230 mm
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Map Vs Scale
Map is the orthographic projection whereas an aerial
photograph is a central projection i.e. perspective projection Map has a single constant scale whereas it varies from point
to point depending upon their elevations on an aerial
photograph.
The amount of details on a map are selective but in an aerial
photograph a wealth of detail is there. Due to symbolic representation the clarity of details is more
on maps than on a photograph.
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Photogram
A photogram is a photographic image made without a camera
by placing objects directly onto the surface of a light-sensitivematerial such as photographic paper and then exposing it to
light. The usual result is a negative shadow image that shows
variations in tone that depends upon the transparency of the
objects used. Areas of the paper that have received no light
appear white; those exposed through transparent or semi-transparent objects appear grey
Ph (C d )
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Photogram (Contd..)
Ph t (C td )
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Photogram (Contd..)
Generation of a photogram: A spatially extended light source (1) illuminates
objects (2 and 3) that are placed directly in front of a sheet of photosensitive
paper. Depending on the object's distance to the paper their shadows look
harder (7) or softer (5). Areas of the paper that are in total shadow (6) stay
white; they become grey if the objects are transparent or translucent; areas
that are fully exposed to the light (4) are blackened.
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Geometry of Vertical Photograph
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Geometry of Vertical Photograph
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33
G t f Ph t h
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Geometry of Photographs
Photo axis: the right-angled xy-axis formed by joining the
opposite fiducial marks of the photograph. This is the axis
from which photo coordinates are measured. The x-axis
approximates to the direction of flight
Optical axis: the line LpP from the lens centre at 90 to the
plane of the photograph.
Geometry of Photographs
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Geometry of Photographs
Principal distance:the distance Lp = f , from the lens to the
plane of the photograph. The principal distance may be
referred to as the focal length. Vertical axis:the line LvV in the direction of gravity, so 90
to a level datum plane.
Tilt:the angle between the vertical and optical axes (see
also principal line).
G t f Ph t h (C td )
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Geometry of Photographs (Contd..)
Principal point (PP): the point p where
the optical axis cuts the photograph, andcoincides with the origin of the photo
axes.
Plumb point: the point v where the
vertical axis cuts the photograph.
Isocentre:the point i, where thebisector of the angle of tilt cuts
the photograph.
Geometry of Photographs (Contd )
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Geometry of Photographs (Contd..)
Plate parallels:the lines at 90to the principal line; they are level lines.
Isometric parallel:the plate parallel passing through the isocentre and
forming the axis of tilt of the photograph.
Flying height:the vertical height of the lens above ground at exposure.
It is the height of the lens above datum (e.g. MSL) minus the mean
height of the terrain.
Swing: the angle s measured in the plane of the photograph,
clockwise from the +y axis to the plumb point. It defines the directionof tilt relative to the photo axes.
Geometry of Photographs
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Geometry of Photographs
The photographic nadir is defined
by the intersection with the
photograph of the vertical line thatintersects the ground nadir and the
center of the lens (i.e. the image of
the ground nadir)
The ground nadiris defined as thepoint on the ground vertically
beneath the center of the camera
lens at the time the photograph
was taken.
Perspective geometry of vertical photographs
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Perspective geometry of vertical photographs
points v and V (ground and photo
nadir point),
i and I (ground and photo
isocentre)p and P (ground and photo principalpoint)
photographic plane
horizontal plane
principle plane
Principle line
(UP)
Perspective geometry of vertical photographs
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Perspective geometry of vertical photographs
* The figure shows camera
axis SP of a camera,
perpendicular to thephotographic plane ABCD,
tilted at angle from the
vertical at exposure so that
the plane of the photograph
itself is inclined by an angle to the horizontal plane
CDEF, representing a level
ground. S represents
perspective center as
defined by the inner or rearnode of the lens system.
Perspective geometry of vertical photographs
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Perspective geometry of vertical photographs
Perspective Axis: Line
CD where the two
plane meet is called
the perspective axis or
horizontal trace.
Perspective geometry of vertical photographs
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Perspective geometry of vertical photographs
Horizontal lines drawnin the photo plane are
called plate parallels
or plate horizontals.
Line iI is the bisector
of tilt angle . It meets
photo plane at i and
ground plane at I.These points are
known as photo
isocentre and ground
isocentre respectively.
Perspective geometry of vertical photographs
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Perspective geometry of vertical photographs
Principal plane: A
plane containing P, V,and S is called the
principal plane. Photo
principal line (VP) and
ground principal lines(vp) are contained in
this plane.
Perspective geometry of vertical photographs
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Perspective geometry of vertical photographs
Isomertric Plate
Parallel: For a truly verticalphotograph taken from exposurestation S, various photo plate
parallels are lines I'I", P'P", etc.
The plate parallel through I is
also called isometric plateparallel.
E t i O i t ti
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Exterior Orientation
Exterior Orientation
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Exterior Orientation
Details on Aerial Photographs
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Details on Aerial Photographs
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48
Details on Aerial Photographs
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Details on Aerial Photographs
Scale and its variation due to ground relief
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Scale and its variation due to ground relief
Ground Coordinates from vertical photograph
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p g p
Ground Coordinates from vertical photograph
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p g p
Image displacement due to ground relief
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Image displacement due to ground relief
Image displacement due to ground relief
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g p g
Image displacement due to ground relief
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g p g
Image displacement due to ground relief
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g p g
Image displacement due to ground relief
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g p g
Image displacement due to ground relief
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Amount function of:
Flying height Distance from nadir point to image point
Elevation of ground point
Position of point w.r.t. principal line and axis of tilt
Relief displacement Will be less on upward side of photo
Identical along axis of tilt
Greater on downward half of photo
g p g
Image displacement due to ground relief
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g p g
FLYING HEIGHT OF A VERTICAL PHOTOGRAPH
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FLYING HEIGHT OF A VERTICAL PHOTOGRAPH
FLYING HEIGHT OF A VERTICAL PHOTOGRAPH
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FLYING HEIGHT OF A VERTICAL PHOTOGRAPH
FLYING HEIGHT OF A VERTICAL PHOTOGRAPH
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FLYING HEIGHT OF A VERTICAL PHOTOGRAPH
Tilted Photograph
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Tilted Photograph
Tilted Photograph
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g p
Tilt angle (t) :It is the angle
between the optical axis
and the vertical axis
Principal Plane: It is the
vertical plane through the
optical axis. Since the plane
of the photograph is normalto the optical axis, it is
normal to the principal
plane.
Tilted Photograph
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g
Principal Line: The line of
intersection of the principal
plane and the plane of thephotograph, which is line no
prolonged, is termed the
principal line.
X-Axis and Y-AxisIn the photograph, the x axis is
placed on the line at which this
vertical plane intersects the
plane of the photograph, with x
values increasing in thedirection of flight. The y axis is
normal to the x axis, and the
origin lies at o. The y axis is
normal to the x axis, and the
origin lies at o.
Tilted Photograph
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Tilt Displacement
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Vertical Aerial Photographs
Ground
Nadir
Isocenter
PPoint
X-axis tilt:
wings upor down
Ground
Nadir
Isocenter
PPoint
Y-axis tilt:
Nose upor down
FOR 220 Aerial Photo Interpretation and Forest Measurements
Definitions
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Definitions
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Link
Link1
Link2
Auxiliary Coordinate System
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Auxiliary Coordinate System
In tilt-swing-azimuth system, auxiliary coordinate
system required for some computationsTwo stages:
Rotate about principal point through an angle
Translate along principal line from principal point
to nadir pointOrigin at nadir point, y axis coincides with the
principal line, x axis is perpendicular to principal
line at the nadir point, clockwise 90o
sincos aa yxx
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= Amount of rotation = s-180o
s = swing angle cossin aa yxy +
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Auxiliary Coordinate System
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Auxiliary Coordinate System
s180
Note: if rotation angle defined as
tfyxy
yxx
tancossin
sincos
+++
Then auxiliary coordinate system can be
expressed as
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Scale of Tilted Photograph
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In previous figure
wk is perpendicular to line Ln and is therefore ahorizontal line
wp is perpendicular to the principal line and is
also a horizontal line Plane kwpis horizontal plane
Plane NWPis horizontal plane
g p
Link
Scale of Tilted Photograph
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g p
Scale between planes kwp & NWP found by
similar triangles
Because Lk = Ln kn = f sec t y sin t
hH
tyt
f
hH
tytfS
hH
Lk
LN
Lk
NP
kp
sincossinsec
''
Link
GROUND COORDINATES FROM TILTED PHOTO
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hH
tyt
f
X
x
WP
wp
sincos
x
tyt
fhHX
sin
cos
On ground, the Y-axis lies principal plane
In figure, wp = x and WP = X, then from
scale:
Link
GROUND COORDINATES FROM TILTED PHOTO
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hH
tyt
f
Y
ty
Y
tnw
Y
kw
NW
kw
sincoscos'cos
ty
tyt
f
hHY cos
sincos
Similarly
Tilt Displacement
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Tilt Displacement
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f
tydor
yt
f
yd
sin)(
sin
)( 2*
*
2*
Parallax and Stereoscopic vision
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Parallaxis defined as the apparent shift in the position of
an object, caused by a shift in the position of the viewer.
Stereoscopic vision is that particular application of
binocular vision (simultaneous vision with both eyes) that
enables an observer to view two different perspective
photographs of an object (such as two photographs takenfrom different camera stations) and get the mental
impression of three dimensions.
A stereoscope permits each eye to see as one a pair ofphotographs that shows an area from different exposure
points and thereby produces a three-dimensional
(stereoscopic) image (model).
STEREOSCOPIC DEPTH PERCEPTION
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STEREOSCOPIC DEPTH PERCEPTION
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Stereo Model
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Stereo Model
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The parallactic angle, also known as the convergence angle, is formed by the
intersection of the left eye's line of sight with that of the right eye. The closer this
point of intersection is to the eyes, the larger the convergence angle. The brainperceives the height of an object by associating depth at its top and its base with the
convergence angles formed by viewing the top and base.
The X parallax and the parallactic angle are related. As X parallax increases, so too
does the parallactic angle.
As the eyes scan overlapping areas between a stereo image pair, the brain receives
a continuous 3-D impression of the ground. This is caused by the brain constantly
perceiving the changing parallactic angles of an infinite number of image points
making up the terrain. The perceived 'virtual' 3-D model is known as a stereomodel
Stereo Model
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If the negatives are now printed as
photographs and viewed
simultaneously, so that the left eyesees only the left photograph and
the right eye only the right
photograph, then a three-
dimensional image will form in the
mind. The above condition can bemost easily obtained by viewing the
photographs under a stereoscope.
The three-dimensional image
formed is termed a stereo model.
stereo pair
Stereo Model
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The stereo model is usually exaggerated and this can be useful in the
heighting process, particularly where the terrain is relatively flat. This
effect can be increased or reduced when planning the photography.
If the value of f is fixed, then from the base/height ratio, it can be seen
that to halve the flying height would double the impression of height.
Increasing the viewing distance of the stereoscope produces aproportionate increase in the impression of height.
VIEWING PHOTOS STEREOSCOPICALLY
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Parallax Measurement
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parallax ofA (PA).
Parallax
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A appears at a1
when viewed from
L1; and at a2when
viewed from L2.
By overlapping the two
photographs, the apparentmovement ofA is shown
as a1a2, (L1a2is parallel to
L2a2)
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Parallax Equation
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Parallax Equation
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Parallax Equation
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Parallax Equation
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Parallax Equation
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X Parallax
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X parallax, which is also known as stereoscopic parallax, is
caused by a shift in the position of observation. To generate a
stereo pair of aerial photos, a camera on board an aircrafttakes pictures of the Earth at different times and thus from
different positions.
Satellite image stereo pairs are generated when a satellitecollects data with two different look angles or two different
beam positions. The change in observation points causes an
apparent shift in the position of an object with respect to the
image frame of reference.
X Parallax
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Two fundamental aspects of stereoscopic parallax are:
the parallax of any point is directly related to the elevation ofthat point; and
the parallax is greater for higher than lower elevations
provided the viewing angle is constant.
These two relationships allow height measurements to be
made from a stereo pair.
Stereo photographs
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Stereo photographs
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Stereo Model: Vertical Exaggeration
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Vertical exaggeration is present in all stereo pairs. It exists because of
disparity between the vertical and horizontal scales of a stereo model.
Under normal conditions, the vertical scale will appear greater than thehorizontal. Image interpreters must take this effect into consideration
when estimating heights of objects and rates of slopes.
Vertical exaggeration is best understood by considering the
relationship between the imaging geometry and the viewing geometryof a stereo model.
Vertical exaggeration is the difference between the imaging base to
height (Bn/Hn) and the stereo-viewing base to height (Bs/Hs) ratios.
Bn/Hnis the ratio of the air base (distance between the two exposurestations) to the flight altitude above average ground. Bs/Hsis the ratio
of the eye base to the distance from the eyes at which the stereo-
model is viewed.
Stereo Model: Vertical Exaggeration
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Stereo Model: Vertical Exaggeration
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Stereo Model: Vertical Exaggeration
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Stereo Model: Vertical Exaggeration
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ELEVATION BY PARALLAX DIFFERENCES
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ELEVATION BY PARALLAX DIFFERENCES
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ELEVATION BY PARALLAX DIFFERENCES
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Stereoscopic Parallax
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Differential Parallax (dp)
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Pseudoscopic Effect
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Another illusion we might encounter is accidentally
reversing the two photos so that the right eye viewsthe left photo and the left eye views the right photo.
The result is a pseudoscopic view, or reversal of
relief, a phenomenon illustrated in Figure in nextslide
Height Calculation
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STEREOSCOPES
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Si l i bl i i d
STEREOSCOPES
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Simple instruments to enable stereo vision and
magnification: see each photo separately through a lens
They can be:
a) Pocket stereo scopes
- the simplest
Note that because of the small base, the photographs must be
on top of each other.
Does not enable viewing of the entire stereo coverage
at the same time.
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b) Mirror Stereoscope
The eye base is increased by a system of mirrors
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The eye base is increased by a system of mirrors
Thus, the entire stereo model can be viewed.
In general, the eyebase, the direction of flight, and the line joiningthe centers of the lenses should be parallel.
Measurement of Parallax
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Parallax Bar
Parallax determination using a Parallax Bar
The parallax bar is a measuring device to measure the x
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The parallax bar is a measuring device to measure the x
parallax of points in a fast and precise manner.
Since x parallax is a function of relief or heights of points
Parallax determination using a Parallax Bar (Contd..)
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Since x parallax is a function of relief or heights of points
above datum, elevations of points can be computed by
measuring their parallax. Other values can also be derived if unknown such as the
flying height, or air base.
To measure parallax of a point you can :
a) Either measure in mono: measure the value of the xcoordinate of the point on each photograph and subtract
the left from the right value. For example, if point a
appears on Left and right photos then:
pa=xaLxar
Or measure in stereo using a parallax bar Put the
Parallax determination using a Parallax Bar (Contd..)
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Or measure in stereo using a parallax bar. Put the
photos on a table under a stereoscope, move them right
and left up and down until you see comfortably in stereo,in this case: air base B as photo base b: o1 o2, and the
center of the lenses of the device must be in the same
direction
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The image of each photo nadir, P.P in a vertical photo (o1and o2)
appears on the other photo
Parallax of b = Ddb = xbxbnote that xb is negative)
L Photo
base b
R Photo
base b
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pa= xaxa= D (C ra) = (D C) + raAssume that k = (D C)Since D and C are constants, then k is a constant, called the parallax bar
constant for the setup, then,
pa = k +r
To calculate the parallax of a point you measure the value r for it
Parallax determination using a Parallax Bar (Contd..)
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To calculate the parallax of a point, you measure the value r for it
with a parallax bar and multiply it by the constant K, you can do that
in stereo for a set of points in few minutes. Now, how to compute the constant K??
It is computed only once by measuring the parallax of two point
monoscopically by measuring their x coordinate on each photo and
subtract: p = x- x1
Now measure the value (r) for each point and apply the equation:
k = pr
You get two values for k, take the average.
You can use photo centers for this process since the x value of eachone on its own photograph is 0, you just need to measure its x value
on the other photo
Without the bar using a precise ruler measure the values
Parallax determination using a Parallax Bar : Summary
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Without the bar, using a precise ruler measure the values
of x of two points a and b on both photos, well distinctive
points
Calculate the parallax of the two points, where:
pa = xaxa andpb= ybyb
Use the parallax bar to measure raand rbfro the samepoints.
Compute k1= para and k2= pbrb
K is the average = (k1+ k2)/2 For any point measure r with the bar and multiply by k to
get the parallax
ExampleA pair of overlapping vertical photographs were taken from a flying
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A pair of overlapping vertical photographs were taken from a flying
height of 4045 feet with a 152.4 mm focal length camera. The air base
was1280 feet and parallax bar readings of 12.57 and 13.04 mm wereobtained with the floating mark set on principal points (ol) and (o2)
respectively. If b and b ( left and right photo bases) were measured as
93.73 and 93.30mm. Parallax bar readings of 10.96 and 15.27 mm were
taken on points A and B. Also the x and y photo coordinates of points A
and B were Xa = 53.41 mm, Ya = 50.84mm , Xb= 88.92mm and Yb=-
46.69mm Calculate the elevations of points A and B
and the horizontal distance between them.
Solution:
Parallax of Point 01=Po1= b'= 93.30mm .
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1 o1
Parallax of Point O2= Po2= b = 93.73mm
Equation of parallax bar: P =K+r K = P - r
For point 01 : k1=Po1- ro1=93.30 -12.57 = 80.73mm
For Point 02 : k2=P02-r02=93.73 -13.04 = 80.69mm
For point a: Pa= k + ra= 80.71+ 10.96= 9l.67mm.
For point b : Pb= k + rb= 80.71+ 15.27= 95.98mm ,
Elevations of points:
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Stereoscopic Plotters
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Stereoscopic plotters are instruments used to measure
ground coordinates of points in the overlapped areaby measuring their photo coordinates in stereo mode.
Two overlapping photos are used, either placed in
projectors as the case in early models, or displayed indigital format as current technology.
Such plotters allow for the removal of the Y parallax,
the effect of different of scale between the photos, tilt
of photos,
Stereo plotters may be classified into three categories:
1- Analogue Optical
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g p
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Film or transparent photos are positioned on theprojectors, light is projected through them, their
l ti iti dj t d t f d l t
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relative positions are adjusted to form a model to
scale. Points are measured as they are traced on the tracing
table (4) in the graph above, a pencil at (11) will draw
a map as the tracing table is moved.
Such a device is used to illustrate the idea, but not
for production today.
2- Analytical Plotters Still uses photographs, but the model is
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St uses p otog ap s, but t e ode smathematical,
Two comparators are used to precisely measurephoto coordinates, which are recorded digitally.
The stereo-model is seen through optics as acomputer adjusts the photos for stereo viewing andmeasurements as the mouse is moved by drivingservo motors.
A point is digitized by clicking a mouse when the
floating mark rests on it to store the coordinates. The digital output is stored and a CAD system canbe used to produce a map, on he fly if needed
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Zeiss P3 analytical plotter 3- Softcopy Photogrammetric Workstations
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Softcopy workstations employ digital images, a
software, a stereovision system, installed on apowerful computer.
The output is totally digital, and many operations are
automated. Softcopy is the current technology used for
photogrammetric measurements.
Images are captured by a digital camera, or scanningphotographs.
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Ortho-photos
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Orthographic projection of photographs.
Uniform scale, no relief displacement.
Serve as maps, what is difference between a
map and a photograph.
now mainly through digital image processing.
If tilt displacement is also removed, you get
ortho-rectified image
Advantage of orthophoto maps
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Orthophoto of Washington, DC
Parallax Summary
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Interior Orientation
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146
Exterior Orientation
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Y Parallax
Y parallax is present in many stereo pairs. It is the difference in
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Y parallax is present in many stereo pairs. It is the difference in
perpendicular distances between two images of a point from the
vertical plane which contains the air base. It can be caused by one or
both images being tiltedwith respect to an exterior coordinate system.
Tilt can occur as a result of roll, pitch and yaw of an aircraft. Y parallax
can also be caused by a variation in flying heights, or if images are
printed at slightly different scales. Finally, Y parallax can occur if the
viewer lines up the images incorrectly.
In small amounts, Y parallax can cause eyestrain, however, the brain
compensates and the 3-D stereo-model remains viewable. In large
amounts, Y parallax makes stereo viewing of an image pair
impossible..
Y Parallax (Contd..)
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The Y-parallax is caused due to the following reasons:
Unequal flying height
Photographic tilt
Misalignment of flight line
Misalignment of stereoscope
Great difference in parallax between adjacent images (in highly
mountainous/rugged terrain)
Y Parallax (Contd..)
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Y Parallax (Contd..)
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Y Parallax (Contd..)
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Aerial Photography mission
When a mapping project requires aerial photographs, one of the first tasks
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is to select the photo scale factor, type of the lens to used, type of the to be
used and the desired overlap for stereo viewing. Forward overlap usually
around 60%, while sideways overlap is around 20%. Furthermore, the date,
time and season of photography should be considered for light condition
and shadow effect.
If the required scale is defined, the following parameters can be
determined.
Flying height required above the terrain.
Ground coverage of a single photograph.
Number of photo required along a flight line.
Number of flight lines required.
Mission Planning:
Aerial Photography mission
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Mission Planning:
Inpu ts for Fl ight Plann ing
1. Area extents (lat / long)
2. Scale of photography
3. Focal length
4. Format size
5. Forward and lateral overlaps
6. Average terrain heights
Software used for Fl ight Plannin g
- World Wide Mission Planning
Navigation
- Computer Controlled Navigational System with GPS
Flight Planning
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Successofphotogrammetricprojectdepends onacquisitionof
goodqualitypictures
Due to weather and ground conditions, time frame for
photographyislimited
Reflightsareexpensiveandcauseslong delaysonprojectMissionmustbecarefullyplannedand executedaccordingto
flightplan
Consists of flight map, (where photos should be taken) and
specifications
E h h t ti ll th
Stereo pair
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Eachphotocoverspartiallythesamearea
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Overlaps
F d l E dl
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Commonareacoveredbytwosuccessive photosofthesameflightlineorstrip Usually60%5%
LateraloverlaporSidelap
Commonareacoveredbytwoadjacentflight Lines.
About25-30%10% (generally30%)
Forward overlap or Endlap
OverlapDirection of
flight
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Overlap
Forward
overlap/Endlap
Lateral
overlap/Sidelap
Flight lines
Flight Plan
What the aircrew has to do as indicated
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Whattheaircrewhastodoasindicated
byflightlines
Thedesignofaerialphotographyflight inorder
toobtaindesiredphotosata certainscale, i.e.,howtheaircrewwill fly(wheretoputtheflight
lines,how high,etc.)
Wh i j t ?
Flight Planning: Critical Issue
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Where is project area?
How many photos needed to cover the area atdesired scale and resolution.
When is the target in desirable condition?
Is stereo viewing necessary?Are quantitative reflectance standards
necessary?
Rules in determining flight line direction
Generally follows four cardinal directions East-
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Generally follows four cardinal directions East
West(E-W)orNorth-South(N-S) Shouldbealongthelongerdimensionofthe area
If over mountain ridges or valleys, go along the
direction of the features to maintain an almost
constant scale; if a flight line crosses mountains,
scale will be smaller in the valley than in the
mountains
Drift and Crab
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Drift Crab
Drift
Drif t is the lateral shift of the aircraft from the
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Drif t is the lateral shift of the aircraft from the
flightline; this may be caused by pilot error or theeffect of wind on the aircraft.
Crab
Crab occurs when the aircraft is not oriented with
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Craboccurs when the aircraft is not oriented with
the flightline; photo edges are not parallel to theflightline and it usually occurs when the pilot is
trying to compensate for a cross wind and orients
the plane into the wind to maintain the flightline.
wind coming from the South will require an
Crab (Contd..)
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airplane flying East to use a crab angle into the
wind in order to fly due East.
For example, the crab angle may be determined
to be 3 degrees, and the airplane will need to fly a
heading of 93in order to achieve a course along90East.
This will affect the camera on board the aircraft.
The crab angle will need to be compensated for in
order to photograph along straight lines on theground
Direction of Flight Lines
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AB
Required Data for Flight Planning
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ProjectareaboundaryCamerafocallength3.5,6,or12
Photoformatsizestandardis9or23cm
Photoscale
Overlaprequirements(inpercentage)
percentageofendlaporsidelapTo be moreeconomical
Leastnumberofexposures
Leastnumberofflightlines
Flight Planning Computations
Fl i h i ht
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FlyingheightDistancebetweenexposuresorAirbase(B)Distancebetweenflightlines
TotalnumberofexposuresFlyingheightabovemeansealevelofeachflightline
Totaltimeneededforphotography
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Typical Flight Plan
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Flying Height
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Hmgef*sp
Distance Between Exposures
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Distance Between Exposures
Example:
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Example:
Given:scale=1:15,000
f.o.=60%
s.l.=30%
s=9=23cm
Required: De
Distance Between Exposures
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Solution:
De(15,000)(23)(1- 0.60)
De138,000cm1,380m
De1.38km
Distance Between Flight Lines
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DflDf S(1s.l.)Where:
S = equivalent ground length of the photoformatsize (s)
S = (sp)(s)
s.l. = sidelap (in decimals)
s = photoformat size
sp= photoscale factor
Distance Between Exposures
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Example:
Given:
scale=1:15,000f.o.=60%
s.l.=30%
s=9=23cm
Required: Df
Solution:
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Df (15,000)(23)(1 0.30)Df 241,500 cm 2,415 m
Df 2.42 km
Total Number of Exposures
total number of exposures
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total number of exposures
(number of exposures per flight line) *
(number of flight lines)
Total Number of Exposures
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Flying Height of Each Flight Line(above Mean Sea Level)
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HmslHmge+m.g.e
Total Time of Photography
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Total Time of Photography
Example:
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Given:scale=1:15,000
f.o.=60%
s=9=23cm
averagevelocityofaircraft=300kph
20exposuresperflightline
10flightlines
Required: t
Total Time of Photography
Solution:
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De(15,000)(23)(10.60)
De138,000cm1,380m1.38km
No. of Photographs
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No. of Photographs
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No. of Photographs
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No. of Photographs
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It is an array of overlapping aerial photographssystematically assembled to form a continuous
AERIAL MOSAICS
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systematically assembled to form a continuous
pictorial representation of a terrainPlanning purpose.
It provides the overview of the terrain- nature and
distribution of the materials and features occupyingthe terrain.
Scale variation from photo to photo will be knowncausing gap in the overlap
A mosaic annotated with local information onrivers,villages etc helps in knowing about thegeographic position of the area interpreted.
Types of mosaics
Uncontrolled mosaic: The photographs are
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oriented in to a position by matching correspondingimages on adjacent photos.
Semi-controlled mosaic: This is a compilation ofphotographs without using rectified photographs
but using control for positioning of eachphotograph.
Controlled mosaic: It is a compilation of scaledand rectified photographs assembled to fit plotted
controlled points.
Mosaics
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Thanks for Listening