UNIT II Introduction to Photo Gramme Try (1)

8/2/2019 UNIT II Introduction to Photo Gramme Try (1)

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UNIT II

Photogrammetry



• 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



Photogrammetry

• Is the act of making plans or maps from

photographs.

• It differs from conventional survey by

minimizing the field work.



Photogrammetry is the technique of

measuring objects (2D or 3D) fromphotographs

Its most important feature isthe fact, that the objects are

measured without beingtouched.



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.



Is This a real CAR ? ?



NOW YOU CAN TELL !!



Broad Areas of Photogrammetry

• Metric Photogrammetry – Making precise

measurements from the photos.

• Interpretative Photogrammetry – Identifying

objects from the photo.



Branches of Photogrammetry

• Terrestrial Photography

• Aerial Photography

• Satellite Photography

Stereoscopic Photography – Photos taken in pairs at

cameras at two ends of a base line.



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.



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.



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.



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



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



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



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.



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.



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.



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



Basic Definitions

• Flight Strip – Photos are taken along a series

of parallel passes.



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%)



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.



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



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.



Image Interpretation Keys

• The Factors that helps in identifying the

feature on an Satellite or Aerial Images/

Photos are called Image Interpretation Keys.



Keys

• Size

• Shape

• Tone / Color

• Texture

• Pattern

• Association

• Shadow

• Site / Location



Size



Shape



Tone



Texture



Pattern



Association



Shadow



Site

UNIT II Introduction to Photo Gramme Try (1)

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