Concept of Photogrammetry For Civil Engineering Student

1. PHOTOGRAMMATIC SURVEY

2. INTRODUCTION
 Photogrammetric surveying or photogrammetry is the science & art of obtaining
accurate measurement by use of photograph.
 For various purpose such as the construction of planimetric & topographic map,
classification of soil, interpretation of geology, Acquisition of military intelligence &
the preparation of composite picture of the ground.
 Photogrammetry is the science & art of obtaining information about physical object by
use of photograph.

3. PHOTOGRAMMETRY INCLUDES
 Taking photograph of object
 Processing the photographs
 Measuring the photographs & reducing the measurement to produce the end result such
as preparing a topographic map.

4. TYPES OF PHOTOGRAMMETRY
 Aerial Photogrammetry : is the branch of photogrammetry in which photographs of the
area are taken by a camera mounted in an Aircraft.
 Terrestrial Photogrammetry : is the branch of photogrammetry in which photographs of
the area are taken by a camera fixed on or near the ground.
 Space Photogrammetry : Is the branch of photogrammetry in which photograph are
taken by camera fixed in space the camera kept in an artificial satellite.

5. TYPES OF PHOTOGRAMMETRY
 Close Range Photogrammetry : is the branch of photogrammetry in which the camera is
kept quite close to the object to obtain the detailed information about the object.
 It is used in Surgery, Architecture, Laboratory investigation etc.

6. USES OF PHOTOGRAMMETRY
 Preparation of topographic maps.
 Classification of soil used for agriculture & forest development.
 Geological investigation to identify & interpret rocks, faults, dip etc.
 Military intelligence for strategic planning of security of country.
 Mining
 Monitoring wild life & forest cover.
 Land use classification

7. LIMITATION OF PHOTOGRAMMETRY
 Unsuitable for dense forest & flat sands due to the difficulty of identify points upon the
pair of photographs.
 It is also unsuitable for plat terrain where contour plans are required.
 It require skilled & experience person.
 It is expensive for survey of small area.

8. USES OF PHOTOGRAMMETRY
 The main advantages of photographic survey is large area can be surveyed in very less
time compared to conventional methods of surveying. Measurements obtained with
photographic survey are more accurate.
 Photographic survey is very expensive. It requires well trained skilled & experienced
professionals to accomplish the survey & map preparation task. Aerial survey may not
be suitable for wide spread forest or desert areas.

9. USES OF PHOTOGRAMMETRY
 Mains use of aerial survey is to prepare plans, maps, photomaps & mosaics of large
area. Over & above it can be used for following applications.
 Military Intelligence : for strategic planning of security of country & during war to
map military camps of enemy.
 Soil Classification : to prepare maps showing types of soil over particular area may be
used for agriculture or forest development.

10. USES OF PHOTOGRAMMETRY
 Land use classification : Aerial survey is convenient to classify area based on use of
area, i.e. Industrial, residential, commercial, agriculture, etc.
 Geological Investigation : Photomaps & mosaics can be used to identify or interpret
rocks, fault, dip etc.
 Law & Order : Aerial survey can be used for planning security for large public
gathering like republic day parade or kumbh mela.

11. USES OF PHOTOGRAMMETRY
 Satellite Image Interpretation : For ground truth verification of training areas of
satellite images & interpretation of images photogrammetry is very useful &
convenient.

12. AERIAL CAMERA

13. AERIAL CAMERA

14. AERIAL CAMERA
 Aerial camera analog type consisting mechanical components & photosensitive emulsion
film or may be digital type having electronic shutter & digital sensor.
 Digital Sensor are made couple charged detector (CCD) known as pixel.
 It consist of fast lenses, high speed shutter, high speed films & large magazine
compartment to hold rolls of film.
 Camera shutter opens for 1/100 sec to 1/1000 sec & allows the light reflected from
various point of view to enter camera & pass through lenses & fall on photo – sensitive
emulsion film.
 High speed shutter prevents blurring if image caused by camera vibration & forward
motion of aircraft.

15. AERIAL CAMERA
 Physical opening of lenses is controlled by diaphragm. The filter prevents haphazard
unwanted light in the atmosphere caused by haze, moisture & flying particles.
 Exposed & unexposed films are rolled in magazine. The film is positioned flat at focal
plane by tension with mechanical pressure.
 Camera record time of each exposure & date of survey.
 Spirit level is for steadiness of the flight.
 A digital counter for numbering photographs & flying height, which is required at time
of interpretation.

16. AERIAL PHOTOGRAPHS
 Aerial photographs are classified based on inclination of camera axis, in following types:
 Vertical photograph : at the time of exposure if axis of camera is vertical or slightly
inclined the photographs obtained are called vertical photographs.
 Oblique photographs : the photograph taken with axis of camera inclined to vertical
line are known as oblique photograph.
 Low oblique photograph : oblique photograph which do not show the line of horizon are called
low oblique photograph.
 High Oblique photograph : Oblique photograph having excessive tilt & showing line of horizon
are known as high oblique photograph.

17. AERIAL PHOTOGRAPHS
 Convergent Photographs : Photograph taken with pair of camera axis inclined to
take photograph are known as convergent photograph.

18. AERIAL PHOTOGRAPHS
 Trimetrogen Photographs : Photograph taken simultaneously from pair of camera,
one with axis vertical & other with slightly tilted are known as Trimetrogen
photograph.

19. DEFINITION
 Camera Axis : Camera axis is the line passing through the center of the camera lens
perpendicular both to the camera plate & picture plane.
 Picture plane : Picture plane is the plane perpendicular to the camera axis at the focal
distance in front of the lens.
 Principal point : Principal point (k or k’) is defined by the intersection of the camera
axis with either the picture plane or the camera plate.

20. DEFINITION
 Focal length : Focal length is the perpendicular distance from the center of the camera
lens to either the picture plate or the camera plate.
 It satisfies the following relation:
 1/f = 1/u +1/v
 Where u & v are conjugate object & image distance

21. DEFINITION
 Focal Plane : Focal plane is the plane in which image of point in the object space of the
lens are focused.
 Nodal Point : Nodal point is either of two point on the special axis of a lens or system.
 Perspective center : perspective center is the point of origin or determination of
bundles of perspective rays.

22. DEFINITION
 Principal distance : when the contact points from original negatives are enlarged
before their use in the completion of subsequent maps, the value of the focal length of
the camera is not applicable to the revised prints. The changed value of f holding the
same geometrical relation is known as principal distance.
 Principal plane : principal plane is plane which contains principal line & the optical
axis. It is perpendicular to the picture plan & the camera plane.
 Print : A print is a photographic copy made by projection or contacts printing from
photographic negative or from a transparent drawing as in blue printing.
 Fiducial Mark : A fiducial mark is one of two, three of four marks located in contact
with the photographic emulsion in a camera image plane to provide a reference line.

23. DEFINITION
 Film base : Film base is a thin, flexible, transparent sheet of cellulous nitrate, cellulose
acetate or similar material which is coated with a light sensitive emulsion & used for
taking photograph.

24. DEFINITION

25. DEFINITION
 Exposure Station (O): The point in the atmosphere occupied by center of camera lenses
at instance of photogrammetry.
 Flying Height (H) : Vertical distance between exposure station & Mean sea level.
 Flight line : Line traced by exposure station in atmosphere. I.e. track of aircraft.
 Horizon point : It is a point of intersection of horizontal line through center of lenses &
principle line on photograph.
 Photo Nadir point (n): It is a point on photograph obtained by dropping vertical line
from camera center. That plumb line extended up to ground gives ground Nadir point.

26. DEFINITION
 Photo principal Point (p): It is a point on photograph obtained by projecting camera axis
to intersect at a point on photograph known as photo principal point (p).
 Principal Plane : Plane defined by exposure station (O), ground Nadir point & Ground
Principal point (P).
 Principal Line : Line of intersection of principal plane with photograph plane. i.e. line np
 Azimuth (A) : Clockwise horizontal angle measured about ground nadir point from true
north to the principal plane of photograph.

27. DEFINITION
 Swing (S) : Angle measured in plane of photograph from +y axis clockwise to photo nadir
point.
 Isocentre (i) : Point on photo where bisection of tilt falls on photo.
 Axis of tit : it is line in plane of photograph perpendicular to principal line at the
Isocentre.

28. DEFINITION

29. SCALE OF PHOTOGRAPH
 The scale of photographs is the ratio of a distance on the photograph to the
corresponding distance on the ground.
 In case of map being an orthographic projection has uniform scale every where on the
map. But incase of photograph, being a perspective projection, the scale of photograph
varies from point to point with change in terrain elevation.
 Where the ground is Horizontal
 Where the ground elevation is variable

30. WHERE THE GROUND IS HORIZONTAL
Scale of Photograph =
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑡𝑤𝑜 𝑝𝑜𝑖𝑛𝑡𝑠 𝑜𝑛 𝑃ℎ𝑜𝑡𝑜𝑔𝑟𝑎𝑝ℎ
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑠𝑎𝑚𝑒 𝑡𝑤𝑜 𝑝𝑜𝑖𝑛𝑡𝑠 𝑜𝑛 𝑡ℎ𝑒 𝑔𝑟𝑜𝑢𝑛𝑑
=
𝑃ℎ𝑜𝑡𝑜 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝐺𝑟𝑜𝑢𝑛𝑑 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒
=
𝑘𝑎
𝐾𝐴
=
𝑜𝐾
𝑂𝐾
=
𝑓
𝐻−ℎ
Where, f= Focal length of the
camera
H = Height of the exposure
station
h= Height of the ground above
M.S.L.

31. WHEN THE GROUND ELEVATION IS VARIABLE
 Let A & B be two point having
elevation ha &hb respectively
above M.S.L.
 They are represented by a&b
respectively on the map.
 The scale of the photograph at
elevation ha =
𝑎𝑝
𝐴𝑃𝑎
 =
𝑂𝑝
𝑂𝑃𝑎
 =
𝑓
𝐻 −ℎ𝑎
 Scale of photograph at elevation ha
=
𝑓
𝐻 −ℎ𝑎

32. WHEN THE GROUND ELEVATION IS VARIABLE
 Let A & B be two point having
elevation ha &hb respectively
above M.S.L.
 They are represented by a&b
respectively on the map.
 The scale of the photograph at
elevation hb =
𝑏𝑝
𝐵𝑃𝑎
 =
𝑂𝑝
𝑂𝑃𝑏
 =
𝑓
𝐻 −ℎ𝑏
 Scale of photograph at elevation ha
=
𝑓
𝐻 −ℎ𝑏
 The scale of the photograph at
elevation his given by S =
𝑓
𝐻 −ℎ

33.  Representative Fraction (R.F) =
1
𝐻−ℎ
𝑓
 It will be inconvenient to calculate scale for each & every point of
photograph. So either Datum scale or Average scale of photograph
can be used.
 Datum Scale : If all the points of photograph are assumed to
be projected on Mean sea level ( Hence R.L. =0.0m)
 Hence h=0.0 m
 Datum scale of Photograph = SD =
𝑓
𝐻
 Average Scale : All the points of photograph are assumed to be
having average elevation above m.s.l.
 Hence = h = havg
 Average scale of Photograph = Savg =
𝑓
𝐻 −ℎ𝑎𝑣𝑔

34.  Scale of the photograph by measuring ground distance :
 Scale of photograph =
𝑃ℎ𝑜𝑡𝑜 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝐺𝑟𝑜𝑢𝑛𝑑 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒
=
𝑙
𝐿
 Scale of photograph from map : in case of a reliable map of the
area is available the photo scale can be found by comparing the
photo distance & the map distance between two well defined
points at the same elevation.

𝑃ℎ𝑜𝑡𝑜 𝑠𝑐𝑎𝑙𝑒
𝑚𝑎𝑝 𝑠𝑐𝑎𝑙𝑒
=
𝑃ℎ𝑜𝑡𝑜 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑚𝑎𝑝 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒

35. PROCEDURE OF AERIAL SURVEY
 Before actually executing aerial survey with camera mounted on aircraft following parameters
are decided prior to flight.
 Altitude Height (H).
 Focal length of camera (f).
 Size of area of land to be photographed
 Size of photograph
 Alignments of flight line & number of parallel flight lines
 Lateral overlaps of photographs
 Number of photograph in each flight line & amount of overlap
 Scale of flight map
 Ground speed of aero plane
 Time interval of exposure of successive photograph.

36. OVERLAPS
 Overlaps of photographs means same ground area in adjacent photographs is common i.e.
same area is viewed by several photograph, that is known as overlap.
 Longitudinal Overlap : Overlap between two successive photographs should be 60% to 70%
& overlap between two alternate photograph should be 10% to 20%.
 Lateral overlaps : Overlap between photographs of adjacent flight line is known as lateral
overlap. This is also known as side overlap. Side overlap should be 20% to 35%.

37. REASONS OF OVERLAPPING PHOTOGRAPHS
 Use full to arrange the photographs in mosaic to have complete view of area.
 Errors of distortion, displacement & tilt can be overcome if overlap is more than 50%.
Excessive distorted photograph can be rejected.
 For measurements of height, photographs can be viewed in 3D-view in stereoscope.

38. CRAB
 When opposite edges of photographs are not parallel to flight line is known as crab of
photograph.
 This may result due to rotation of camera about vertical axis. Crab should be avoided as it
reduces effective area of coverage.

39. DRIFT
 When aircraft is swayed away from its preplanned flight line then it is known as drift.
 This occur due to variation in wind speed & wind direction.

40. PHOTOMAPS & MOSAICS
 Photomaps or mosaics can be used as alternate of maps & plans.
 Photomaps is single photograph.
 Two or more photomaps combined is known as mosaics.
 In mosaics object can easily be recognized as compared to maps.
 In maps symbol of object are used while in mosaics, true pictures of object help in interpreting
photographs.
 Cost & time of preparing mosaics is much less compared to map.
 Mosaics can be used for identifying routes for roads, rail, pipeline, buildings etc.
 Mosaics cannot be used like maps for accurate measurement of distance for engineering
purpose.

41. RELIEF DISPLACEMENT
 When the ground is not horizontal, the scale of the
photograph varies from point to point. Every point
on the photograph is therefore, displayed from
their true orthographic position due to relief of the
object.
 Its elevation above or below a datum. This shift or
displacement is called relief displacement.

42. RELIEF DISPLACEMENT
 Eq. for relief displacement
 Let, r = radial distance a from p
 r0 = radial distance from a0 from p
 R = P0A0
 From similar triangle

𝑓
𝐻 −ℎ
=
𝑟
𝑅
 r =
𝑅𝑓
𝐻 −ℎ
…….eq.(1)
 Also,
𝑓
𝐻
=
𝑟0
𝑅
 r0 =
𝑅𝑓
𝐻
……..eq.(2)

43. RELIEF DISPLACEMENT
 Hence Relief displacement is given by
 d = r – r0

𝑅𝑓
𝐻 −ℎ
=
𝑅𝑓
𝐻
 Rf [
1
𝐻 −ℎ
-
1
𝐻
]
 Rf [
ℎ
𝐻 −ℎ 𝐻
]
 d =
𝑅𝑓ℎ
𝐻(𝐻−ℎ)
…….eq.(3)
 From eq.(1)
 R =
𝑟 (𝐻 −ℎ)
𝑓
 This value put in eq.(3)

44. RELIEF DISPLACEMENT
 d =
𝑟 (𝐻 −ℎ)
𝑓
.
𝑓ℎ
𝐻 (𝐻−ℎ)

𝑟ℎ
𝐻
…..eq.(4)
 Similar from eq.(2) R =
𝑟0𝐻
𝑓
 Put this value in eq.(3)
 d =
𝑟0𝐻
𝑓
.
𝑓ℎ
𝐻 (𝐻 −ℎ)
 d=
𝑟0ℎ
𝐻 −ℎ
…….eq.(5)

45.  Following conclusion made from Relief Displacement
 The relief displacement increase as the distance from the principal point.
 The relief displacement decrease with the increase in the flying height.
 The relief displacement of the point vertically below the exposure station is zero.
 The point above datum the relief displacement is positive(+ve).
 The point below datum the Relief displacement is Negative (-ve).

46. GROUND CO-ORDINATE
 In fig. points A &B on ground having
height ha &hb above M.S.L. appear in
photograph as point a&b.
 The co-ordinates of point A&B at
M.S.L. are (XA,YA)& (XB,YB).
 The co-ordinates of corresponding
points on photograph (xa,ya) &
(xb,yb).
 Scale of photograph for point A=
𝑓
𝐻−ℎ𝐴
 Scale of photograph for point B=
𝑓
𝐻−ℎ𝐵
 Now the co-ordinates distance for point
a & b on photograph are measured.

47.  So, value of xa, ya,xb&yb are measured on photograph &
corresponding values of coordinates on ground computed as
below.
 For point a, Scale =
𝑝ℎ𝑜𝑡𝑜 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑔𝑟𝑜𝑢𝑛𝑑 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
=
𝑥𝑎
𝑋𝐴
=
𝑦𝑎
𝑌𝐴
=
𝑓
𝐻 −ℎ𝐴
 Hence XA =
𝐻 −ℎ𝐴
𝑓
∗ 𝑥𝑎
 And YA =
𝐻 −ℎ𝐴
𝑓
∗ 𝑦𝑎
 Similar point b, Scale =
𝑝ℎ𝑜𝑡𝑜 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑔𝑟𝑜𝑢𝑛𝑑 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
=
𝑥𝑏
𝑋𝐵
=
𝑦𝑏
𝑌𝐵
=
𝑓
𝐻 −ℎ𝐵
 Hence XB =
𝐻 −ℎ𝐵
𝑓
∗ 𝑥𝑏
 And YB =
𝐻 −ℎ𝐵
𝑓
∗ 𝑦𝑏
 The distance between A&B =L = (𝑋𝐴 − 𝑋𝐵)2 + (𝑌𝐴 − 𝑌𝐵)2