Principle of aerial photography and photogrammetry, types of aerial photographs, scale of aerial photograph.

1. Principle of Aerial
Photography
And Types of Photos
By T.SrinivasaRao

2. Contents
• Introduction -> How it works?(planning, common terms and
formation of photo)
• Types of aerial photographs
• Aerial photo vs Map - 1 point for now
• orthogonal vs perspective projection
• Principle of vertical photograph (dissection of taking aerial
photograph)
• Scale
• Stereoscopy
• Map vs Stereoscopy
• Map vs Mosaic

3. Introduction
• Aerial photography has been defined as the science of
taking photograph from a point in the air for the purpose
of making some type of study on earth surface.
• The net result of any photographic mission is
photographic negative.
• photographic negatives are the result of favorable and
unfavorable factors acting simultaneously.
• A good aerial photgraph must have a certain standard of
geometrical accuracy.

4. • Aerial photography and its planning generally includes
selection of types of aeroplane and camera, trend of run,
film and filter combination, which is of great importance
in aerial photo interpretation.
• Most of the conventional aerial photography is done at 1:
30000 to 1:60000 scale on a conventional black and
white panchromatic film.
• The scale of photography further depends on objectives
of the work, which governs the speed of the aircraft and
its flying height, also depends on the type of camera lens
being used.

5. • optimum scale for geological photo interpretation are 1:
25000 to 1:40000
• For regional geological surveys a small scale photograph
of 1:60000 or even smaller is suitable.
• For extensive ground coverage satellite imagery are
most useful.
• In aerial photography for more specific and detailed
information such as geotechnical studies, mineral
exploration, ground water surveys, land-use planning,
and town planning, large scale photographs on
photographs of scale 1:15000 to 1:10000 are most
suitable.

6. • In such type aerial photographs, low speed aeroplanes
(200 to 350kmph) are used and flying height is normally
not more than 8000 to 10000m.
• low flying speed and heights are one of the most
important aspects in obtaining sufficiently large scale
photographs with sharp images of objects.
• There should be complete stereographic coverage of
terrain, i.e., all features of the terrain should occur on
atleast 2 photographs for stereoscopic viewing.

7. • Photographs are taken in runs in the direction of flight in
such a way there will be minimum 60% overlap between
adjacent photos and 30% sidelap between adjacent runs.
• the quality of photographs depends on
– flight and weather conditions
– camera lens
– film and filters
– developing and printing process
• as far as possible photograph should be vertical and
should be free from elements of tilt and tip. Also free from
defects like drift and crab.

9. • Drift -> 2 Successive flight lines should be parallel in
ideal case.
• At high altitudes because of strong wind currents called
sidewinds influence the aeroplane in maintaining
predetermined direction and straightness of run.
• This deviation from the original intended flight path is
called as drift.
• uncorrected drift will result in subsequent photographs
covering more area in the prevailing wind direction.

10. • During sidewinds if pilot tries to maintain original path, he
has to turn the nose of the aeroplane slightly against the
wind.
• this makes the aeroplane to rotate on its vertical axis.
• in this case, original path is maintained but the area
covered by photograph is much different than that planned
in the original.
• the aerial photograph is rotated in the direction opposite to
wind direction here.
• This defect is called as crab.
• The above 2 defects causes reduction in stereoscopic
coverage of the terrain.

13. Types of Aerial Photographs
• Extreme growth in the technology and tecniques used for
acquiring aerial photographs.
• Aerial photographs are classified according to attitude of
camera axis, lens system, types of cameras, types of
films and filters or some special equipment employed in
the camera or techniques to record some special effect
on the film.
• Classification of techniques is done here according to 3
main criteria which are discussed in the next few slides.

14. Types of Aerial Photographs
• Based on orientation of camera axis
– Vertical photographs
– Low oblique photographs
– High oblique photographs
• Based on lens system
– Single lens photography
– Three lens photography(trimetrogon photography)
– Four lens photography
– Nine lens photography
– Continuos strip photography

15. Types of Aerial Photographs
• According to special properties of films, filters or
photographic equipment
– Black and white photography (Panachromatic
photography)
– Infra red photography
– Color photography
– Color infra-red photography
– Thermal infra-red photography
– Radar imagery
– Spectrazonal photography

16. Based on oientation of camera
axis
• aerial photographs are classified according to the
orientation of camera axis at the time of photography.
• Vertical photographs are the ones which are taken with
the axis of camera being vertical at the time of exposure.
• It is virtually impossible to take true vertical photographs.
• Deviation of optical axis from the vertical, if it is in
between 1 to 2 degree, the photographs are called tilted
photographs.

17. Based on oientation of camera
axis
• Oblique photograph is taken with camera intentionally
tilted from the vertical.
• If horizon is captured in the photograph it is called high
oblique photograph.
• If horizon is not captured in the photograph it is called
low oblique photograph.

22. According to Lens System
• Single lens system is most commonly used lens system in
most of the aerial photo interpretation work.
• 2, 3 and multi lens became almost obsolete.
• But some of the multi lens techniques are still being used in
war reconnaissance and in photography researches.
• Trimetrogen system of photography is developed to obtain as
much as coverage for the preperation of maps during the
worldwar - II.
– The system got the name as it uses 3 cameras were
assembled with trimetrogen lens

23. – In this system 2 of the 3 cameras are obliquely
mounted at 60 degree to vertical.
– This will cover photograph upto horizon and some
area in the middle also by the camera which is
mounted vertically.
– all cameras are exposed simultaneously.
– Resulting photographs will cover area from horizon to
horizon in the direction perpendicular to flight line.
– covers more area but scale becomes smaller towards
horizon
– the vertical photgraph has 60% while there is 10 to 30
percent sidelap between vertical and oblique
photographs.

27. • multi lens system consists of 2 to 9 lens in the camera,
and all aquire images simultaneously.
• some times different filters are placed in cameras
depending on requirement.
• in the past continuos strip photographs are also
attempted
– negative is made to pass through a narrow slot in the focal
plane of camera.

30. Aerial photo vs Map
• Aerial Photo:
– Central projection
– Non-Uniform scale
– actual features
• Maps
– orthogonal projection
– uniform scale
– symbols
– imaginary objects presence

31. orthogonal vs perspective
projection

33. Vertical photograph

34. vertical photograph - characteristics
• Tilt < 3 degree
• Scale is approximately constant throughout the photo
• Most common format available is 9x9 square inch
• within limitations a vertical photograph can be used to
substitute a map.
• p = i = n for a vertical photograph
( p - principle point, i - isocenter, n - nadir point)

35. Vertical Aerial Photograph

38. Tilted photograph

39. • C - Perspective center
• c - focal length
• principal point - PP
• camera axis - c-PP

40. • N - Nadir point, is the intersection of the vertical and perspective
center in the photograph
• tilt angle, t - angle between camera and vertical axis
• swing angle, s - angle measured at the pricipal point from the +ve y-
axis counter-clockwise to N
• azimut α is the angle at the ground nadir N measured from the +Y-axis
in the ground system counterclockwise to the intersection O of the
camera axis with the ground surface. It is the azimut of the trace of the
principal plane in the XY -plane of the ground system.
• isocenter I is the intersection of the bisector of angle t with the
photograph. It is on the principal line.

41. Scale

42. More discussion on Scale
• Refer your class notes.