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UNIT II
Photogrammetry
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• Introduction The photogrammetry has been
derived from three Greek words:
– Photos: means light
– Gramma: means something drawn or
written
– Metron: means to measure
• The method was first applied by a French
engineer (Laussedal) in 1861
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Photogrammetry
• Is the act of making plans or maps from
photographs.
• It differs from conventional survey by
minimizing the field work.
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Photogrammetry is the technique of
measuring objects (2D or 3D) fromphotographs
Its most important feature isthe fact, that the objects are
measured without beingtouched.
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PHOTOGRAMMETRY
• objects are measured WITHOUT TOUCHING.
• It is a REMOTESENSING technique.
• It is a close range method of measuring objects.
• It is a 3-dimensional coordinate measuring
technique that uses PHOTORAPHS as thefundamental medium for measurement.
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Is This a real CAR ? ?
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NOW YOU CAN TELL !!
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Broad Areas of Photogrammetry
• Metric Photogrammetry – Making precise
measurements from the photos.
• Interpretative Photogrammetry – Identifying
objects from the photo.
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Branches of Photogrammetry
• Terrestrial Photography
• Aerial Photography
• Satellite Photography
Stereoscopic Photography – Photos taken in pairs at
cameras at two ends of a base line.
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Application of Photographic Survey
• Construction of planimetric and topographic maps.
• Mountains and hilly areas can be surveyed easily.
• Most suitable for reconnaissance.
• Suitable for inaccessible areas, forbidden property and hazardous
area.
• Acquisition of military intelligence.
• Mapping geology and soil.
• Urban area mapping.
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Principles of Photogrammetry
• Triangulation – Involves measurements of
horizontal angle between the stations of a
triangular network.
• Trilateration - Involves measurements of
horizontal distance between the stations of a
triangular network.
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Definitions
Focal Length – Distance between the film plane
and focal point (optical center of the lens)
Principle Focal Length – in a lens all parallel rays
will be focused to a point referred to as the principal
focal point. The distance from the lens to that point
is the principal focal length f of the lens.
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Terrestrial Photography
• Photographs are taken from the Earth surfaceand is used to measure the position andelevation of a point.
• The procedure is similar to the plane tablesurveying.
• The field work consists of
i. Reconnaissanceii. Triangulation
iii. Camera Work
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Phototheodolite
• Combination of cameraand theodolite.
Components
Camera Box and Plates
Vertical Frame (two wirescrossing each other, givesthe principle point)
Tangent Scale
Compass
Photographic Plate
Telescope
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Types of Terrestrial Photogrammetry
• Static – Photos of stationary objects. Slow,
high resolution films are used with long
exposure
• Dynamic – Photos of moving objects. Fast
films and short exposure are used
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Application of Terrestrial Photogrammetry
• Mapping rugged terrain.
• Topographic mapping
•
Used in gorges and rugged mountains• Construction sites, excavation and mining.
• Agri, forestry, archeology, architecture,
medicine and dentistry etc• In measuring speed of vehicles, water current,
plant growth.
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Aerial Photography
• Photographs taken from air through plane.
• Can be taken whenever needed unlike satellite imagery.
• Can have a very high resolution images but can cover
very small area.
•
Gives the advantages of getting stereoscopic images.
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Classification
• Vertical Photo – Taken with vertical camera
axis (more or less)
• If the photo perfectly vertical it is called truly
vertical.
• And if there are some unintentional tilts (1o –
3o ) it is tilted photo.
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Cont…
• Oblique Photos –
Photos taken with
intentional tilt away
from vertical.
– A High Oblique Photo –
Shows horizon
– A Low Oblique Photo – Do not show horizon
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Basic Definitions
• Flight Strip – Photos are taken along a series
of parallel passes.
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Cont…
• Side (Lateral) Lap – Usually the photos are taken
in such a way that the area covered by each
successive photos along a flight strip overlaps a
part of previous flight strip. (20 -25%)
• End Lap – Overlapping in successive photos in a
single flight strip. (60 – 65%)
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Cont…
• Exposure Station – Position of camera at each
exposure
• Flying Height – Altitude of the camera
• Block – Two or more side overlapping strips
used to cover an area.
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Application
• Topographic mapping
• Small scale map used for planning and
designing
• Land surveying, boundary mapping
• Map rugged terrain
•
Saves time and less field work • Forestry, Geology, Irrigation etc
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USES OF PHOTOGRAPHIC SURVEYING
Construction of planimetric and topographic maps.
Mountainous and hilly areas with less number of trees can be very
satisfactorily surveyed.
Aerial surveying is most suitable for reconnaissance.
Suitable for inaccessible regions, forbidden properties, unhealthy
regions, like material affected areas.
Acquisition of military intelligence.
Interpretation of geology and soil details.
Has been largely used for the surveys of building.
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Image Interpretation Keys
• The Factors that helps in identifying the
feature on an Satellite or Aerial Images/
Photos are called Image Interpretation Keys.
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Keys
• Size
• Shape
• Tone / Color
• Texture
• Pattern
• Association
• Shadow
• Site / Location
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Size
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Shape
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Tone
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Texture
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Pattern
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Association
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Shadow
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