aerial photogrammetry, vertical photographs, oblique photographs, low photographs, scale of photo graphs, remote sensing,

1. Photogrammetry
►photo = "picture“,
grammetry = "measurement“, therefore
photogrammetry = “photo-measurement”
►

3. Lecture outline
► Definition
► Principle of photogrammetry.
► Uses.
► Aerial camera
► Aerial photograph.
► Scale of vertical and tilted photograph
► Ground coordinates
► Procedure of aerial survey.
► Photomaps and mosaics
►

4. Introduction
► Definition
of Photogrammetry: the art,
science, and technology of obtaining
information about physical objects and the
environment
by
photographic
and
electromagnetic images.

5. Basic Information
► 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
1:120 with contour intervals
as small as 1 foot.
 Topographic mapping is the most common
form. – U.S.G.S updated and done this way.
 Used to reconstruct a scaled 3-dimensional
optical model of the lands surface using a
stereoplotter.

6. Basic Information
► Uses: Aerial photos
 Aid: geological investigations, soil surveys, land
surveys, tax mapping, reconnaissance and
military intelligence, urban and regional
development,
transportation
system
investigations, quantity estimates, shore
erosion, etc.
 Mathematical methods have been developed to
make precise 3-dimensional measurements
from photos.
►Phototriangulation:
survey stations.
3-dimensional
positioning
of

7. Basic Information Continued
 Photo has been used to take geometric
measurements of human bodies, artificial
human hearts, large radio telescopes, ships,
dams,
buildings
and
very
accurate
reproductions.
► In
general it is not economical for small
projects – the cost break even point is
somewhere between 30 – 100 acres
depending on the situation.

8. Basic Information
► Photogrammetry
can
not be used
successfully over the following types of
terrain.
 Desert or plains areas, sandy beaches, and
snow – the photograph as uniform shades with
little texture.
 Deep canyons or high buildings that conceal
ground surface.
 Areas covered by dense forest.

9. 2 Basic Categories
► Photogrammetry
-
Known
survey
► Classification of photogrammety
as
Aerial

10. 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 imaging – called remote
sensing.

11. Aerial camera

12. Types of Aerial Photographs

13. Principle of Aerial survey

16. Definitions
(GTU:Nov/Dec-2011)
Exposure station (o) : The point in the atmosphere
occupied by center of camera lenses at instance of
photography.
► Flying height : Vertical distance between exposure
station and mean sea level.
► Flight line: Line traced by exposure station in
atmosphere ( track of aircraft)
► Photo principal plane (k) It is point on photograph
obtained by projecting camera axis to intersect at a
point on photograph known as photo principal point(k)
► Camera axis extended up to ground, the point
obtained on ground is called Ground Principal point
(K)
►

17. Definitions
Photo nadir point (n) : It is a point on photograph
obtained by dropping vertical line from camera center.
That plumb line extendd up to ground gives Ground
Nadir Point (N)
► Horizon point (h) : It is point of intersection of
horizontal line through center of lenses and principal
line (np) on photograph.
► Principal plane:- Plane defined by exposure station
(O), Ground nadir point (N) and ground principal point
(P) ( i.e. plane NOK)
► Principal line : Line of intersection of principal plane
with photograph plane -nk
►

18. Definitions
Azimuth : (A) : Clockwise horizontal angle measured
about ground nadir point from true north to the
principal plane of photograph.(Ф )
► Swing (S) :-Angle measured in plane of photograph
from +y axis clockwise to photo nadir point.
► Isocenter (i) :-Point on photo where bisection of tilt
falls on photo. ( dotted line ------- in sketch).
► Axis of tilt:- It is line in plane of photograph
perpendicular to principal line at the isocenter.
►

19. Scale of Photograph

20. 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

21. Scale of a Vertical Photographs
f
f
or
H
H’
h
► 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 =

22. Scale of a Vertical Photo

23. 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.) =

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

25. 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
►
►

26. Relief Displacement
►
►
Relief Displacement exists because photos are a
perspective projection.
Use this to determine the height of object:
h= d (H’)
r
h = height of object
d = radial distance to top of object-radial distance to
bottom of object.
r = radial distance to top of object.

27. Relief displacement
► The
scale of an aerial photograph is partly a
function of flying height.
► Thus,
variations in elevation cause
variations in scale on aerial photographs.
Specifically, the higher the elevation of an
object, the farther the object will be
displaced from its actual position away from
the principal point of the photograph (the
point on the ground surface that is directly
below the camera lens).

28. Relief displacement
► The
scale of an aerial photograph is partly a
function of flying height.
► The lower the elevation of an object, the
more it will be displaced toward the
principal point . This effect, called relief
displacement , is illustrated in the diagram
below. Note that the effect increases with
distance from the principal point.

31. Equation for relief displacement (d)

32. 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

34. 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)

35. 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

36. Overlaps

37. Overlaps

38. Overlaps
► Longitudinal
Overlap
► Overlap between
two photo 50% to
70%
► Overlap between
two alternate photo
10% to 20%
► Lateral
Overlap
► Overlap between
adjacent flight lines
► Side overlap should
be 20% to 30%.

39. Reasons for Overlaps
► Arrangement of mosaic
► Remove
errors
due
to
distortion,
displacement, and tilt.
► For view in stereoscope- 3D view.
► Avoid repetition of aerial survey

40. D

42. Numbers of photographs
required to cover the area A

43. Number of photographs
necessary to cover a Given area
► A = Total area to be photographed
► l = length of photo in direction of flight
► w = width of photo normal to direction
► s = Scale Of Photograph
f/H
► L= net ground distance corresponding to l
► W= Net ground width corresponding to w
► a = net ground area covered by each photo
► Pl = % Overlap in direction of flight(length)
► Pw = % overlap in side (width)

44. Numbers of photographs
required to cover the area A

45. ► If
Numbers of photographs
required to cover the area A
actual geometry L and B known no of
photographs calculated as under
►
►
L= Ground length of each photo ( 1-Pl)s.l. in Km
S= speed of aeroplane in Km/hour.

46. Crab
► Opposite
line of photographs are not
parallel to flight line is known as crab of
photograph.

48. Drift
► When
aircraft is swayed away from its
preplanned flight line then it is known as
drift.

52. 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

53. Procedure to prepare Photo
mosaics
► Manual
 Zerox procedure
► Digital
 Photo editing software

54. STEREOSCOPES

55. 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

56. 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.

57. Later……

58. Planning and Executing Photo Project
►
Basic Overall Process:
1.
2.
3.
4.
5.
Photography – obtain suitable photos.
Control – obtain sufficient control through field
surveys and/or extension by photographic
methods.
Map Compilation – plotting of planimetric and/or
topographic features.
Map Completion – map editing and special field
surveys.
Final Map Drafting

59. Elements of Planning
1.
Conversion of requirements to project
specs.
 Factors:
1. Purpose of photogrammetry
a)
Majority of projects for engineering involves making
topographic map in a stereoscopic plotting unit.



Wide angle photography (152mm focal length) is required for
topographic mapping because it provides better vertical
accuracy.
 If area is heavily wooded, use f=210mm (standard angle) to
allow more visibility through trees.
Generally 60% overlap with 15-30% sidelap.
Orientation of flightlines is dictated more by economy than
geometric considerations.

60. Elements of Planning
b)
Photos for mosaics should be flown as high as possible.

c)
Reduces relief displacement.
Orthophotos – similar to topo maps, however, should be
taken normal to ground topo.
2. Photo Scale: somewhat dependent on type of
plotter.


Essentially can be dependent on type of plotter you
need to see and dividing it by the resolving power of the
photo equipment.
Also affected by map accuracy and area configuration.

61. Elements of Planning
3. Allowed scale variation.



Variation caused by difference in ground elevation and
flying height.
Longer focal length reduces scale variation.
If flying height remains constant and ground elevation
increases the area covered by photo becomes less.


Overlap becomes less
Viewfinder needed to control overlap and flightline spacing, thus
eliminating possible gaps.
4. Relief displacement

Affects mosaics most.

Large amount of relief displacement will make it difficult to form
continuous picture desired in mosaics.

62. Elements of Planning


Relief displacement decreases as flying height
increases, the focal length must also be increased.
Relief displacement has no adverse affect on map
making with stereo.

With greater relief displacement, elevations can be measured
and plotted more accurately.
5. Tilt

Amount in direction of flight (y tilt).


Amount normal direction of flight (x tilt).



Will cause overlap to be greater on one end than other.
Will increase sidelap on one side and decrease on other.
Y tilt corrected by viewfinder.
X tilt corrected by increasing planned sidelap.

63. Elements of Planning
6. Crab and Drift

Crab – angle formed between flightline and edges of
photo in direction of flight and caused by not having
focal plane square with direction of flight at time of
exposure.



Corrected by rotation of camera on vertical axis through
viewfinder.
Reduces coverage, but sidelap compensates.
Drift – plane not staying on flightline.

Most common cause of re-flights and gaps.

64. Elements of Planning
7. Flying height: determined after sidelap and
overlap determined.

Factors affecting:
1. Desired scale, relief displacement, and tilt.
2. Precision of equipment used.
 Greater precision, greater possible flying height.


By doubling flying height, ground coverage increased 4
times, thus less ground control and fewer photos.
Vertical accuracy most important in topographic
mapping.
1. Flying height is related to contour interval desired.
 Relationship called C-factor (precision factor)
 Flying height = desired contour interval x C-factor
 C-factor is the value used to compute flying height which
will produce photos satisfactory to obtain the desired
vertical accuracy of the maps.

65. Elements of Planning
8. Direction or orientation of terrain

2.
Arrange to fly along ridges, not across.
Gathering material and people.
1. Existing photos, maps, survey data, instruments
and personnel.
Determine specifications and
conditions for operation.
3. Preparing final plans.
2.
1. Scheduling
2. Surveying instructions
2.
Cost estimating and replanning.

66. Flight Design
A.
Considerations
1.
2.
3.
4.
5.
6.
B.
Project boundaries
Existing and planned control
Time schedule
Final product needed
Optimum flying season
Found cover conditions
Objectives
1. Determine optimum conditions for spacing of photos along
flightlines.
2. Number and spacing of fligtlines to cover area.
3. Plan must account for allowable deviations.
4. Distance between flightlines on fllightway.

67. Flight Design
C.
Flight Patterns
1. Totally dependent on overlap and sidelap.

Under ideal conditions with 9”x 9” photo with 6” focal
length, and overlap of 57%, and sidelap of 13% will
provide maximum stereo coverage with no gaps.

If additional safety factor desired, overlap can be increased to
70-75% and sidelap can be increased to 50%.

68. Computation of Flight Plan
►
Data required to compute flight map lines, time
interval between exposures, and amount of film
needed.
1. Focal length of camera.
2. Flying height above datum or photo scale for certain
elevation.
3. Size of photo.
4. Size of area to be photographed.
5. Positions of outer flight lines with respect to boundary.
6. Overlap.
7. Sidelap.
8. Scale of flight map.
9. Ground speed of aircraft.

69. Example
Area – 15 miles N-S & 8.5 miles E-W
Photos – 9” x 9”
Save tobe 1:12000 @ 700’ above elevation
Overlap – 60%
Sidelap – 35%
Ground speed of plane – 150 mph
Flight lines to be laid out N-S on a map @ a scale
of 1:62500
Outer flight lines coincide with E & W boundary

70. 1.
2.
Flying Height:
1
1
=
∴ H = 12000’ above 700’ or 12700’ above sea level
H 12000
Ground Distance Between Flight lines – since sidelap is 35%, photo
distance between lines is 65% of 9”=5.85”
5.85'×12000
∴ GroundSpacing =
= 5850'
12" / 1'
3.
Number of flight lines
Total width = 8.5 miles x 5280 = 44880’
44880
∴
= 8 + 1 = 9 flight lines (Round up)
5850
4.
Adjust ground distance between flight lines
5.
Spacing of flight lines on flight map
5610 12"
5610’ on map @ 1:62500 scale
×
= 1.08"
62500
44880
= 5610'
9 −1
1'

71. 6.
Ground Distance Between Exposures with 60% overlap gain on
each photo is 40% ∴
40% of 9” = 3.60” ∴
ground distance is: 3.60 × 12000 = 3600'
12" / 1'