INTRODUCTION: OVERVIEW

Photogrammetry is defined by the American Society of Photogrammetry as the art, science

and technology of obtaining reliable information about physical objects and the environment
through the process of recording, measuring, and interpreting photographic images and patterns
of recorded radiant electromagnetic energy and other phenomena.

Metric Photogrammetry – consists of making precise measurements from photos and other
information sources to determine in general the relative location of points. The most common
application of metric photogrammetry is the preparation of planimetric and topographic maps
from photographs

Interpretative Photogrammetry – deals principally in recognizing and identifying objects and

judging their significance through careful and systematic analysis. It includes branches of
photographic interpretation and remote sensing.

Uses of Photogrammetry

1. Land-Use Planning and Mapping

Aerial photography has two uses that are of interest within the context of this course: (1)
Cartographers and planners take detailed measurements from aerial photos in the
preparation of maps. (2) Trained interpreters utilize aerial photos to determine land-use
and environmental conditions, among other things.

Although both maps and aerial photos present a "bird's-eye" view of the earth, aerial
photographs are NOT maps. Maps are orthogonal representations of the earth's surface,
meaning that they are directionally and geometrically accurate (at least within the
limitations imposed by projecting a 3-dimensional object onto 2 dimensions). Aerial
photos, on the other hand, display a high degree of radial distortion. That is, the
topography is distorted, and until corrections are made for the distortion, measurements
made from a photograph are not accurate. Nevertheless, aerial photographs are a
powerful tool for studying the earth's environment.

2. Geologic Mapping
3. Forestry
4. Archaeology
5. Oceanography
6. Architecture
7. Ecology
8. Mineralogy
9. Military Intelligence
10.Space Exploration

Advantages of aerial photography

1. Improved vantage point-allows us to look at the "big picture" which is impossible to
obtain by ground observations.
2. Capability to stop-action-very useful in studying dynamic phenomena such as floods,
moving wildlife populations, traffic, oil spills, and forest fires.

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 3. Permanent recording. Aerial photographs are virtually permanent records of existing
conditions. It can be compared against similar data acquired at previous times, so
that changes over time can be monitored easily.
4. Broadened spectral sensitivity. Film can see certain phenomena the eye cannot.
Invisible UV and near IR energy can be detected and recorded in the form of visible
image.
5. Increased spatial resolution and geometric fidelity. We can obtain accurate
measurements of positions, distances, directions, areas, heights, volumes, and
slopes from airphotos.

TYPES OF AERIAL PHOTOGRAPHS

Aerial photographs may be either vertical or oblique. Vertical photographs can be truly vertical,
or slightly tilted (less than 3o from the vertical). Most aerial photos are tilted to some degree.
Therefore, the use of the term vertical photographs in this chapter assumes truly vertical
photographs, while in reality they might be tilted up to 3 o. Oblique aerial photos are photographs
purposely taken with an angle between 3 and 90 o from the vertical. They can be low oblique (if
the horizon is not visible) or high oblique (if the horizon is visible)

Whether they are vertical or oblique, aerial photographs may be obtained in various formats and
sizes depending on the purpose and the type of application they are used for. The format of
most aerial photographs is square and sometimes rectangular depending on the camera but the
most common format is 23 by 23 centimeters (9 by 9 inches). Vertical and oblique aerial
photographs also have advantages over one another in respect to their usage.

Optical Axis
Camera Lens
Field of View

Vertical Low Oblique High Oblique

Terrestrial photos are taken on the ground. Terrestrial photos are usually oblique or horizontal,
where the axis of the camera is tilted about 90o from the vertical.

Taking Vertical Aerial Photographs

Photographs are usually taken along a series of parallel passes called flight strips. The
photographs are normally expose in such a way that the area covered by each successive
photograph along a flight strip duplicates or overlaps part of the coverage of the previous photo.

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 Coverage of Overlap
one photo

Sidelap

Side lap of adjacent flight strips

SHORT HISTORY OF PHOTOGRAMMETRY

Important dates in the chronological history of photography, aerial photographic interpretation,

and remote sensing:

300 BC - Greek philosopher Aristotle knew that tiny hole in a wall could throw across a
darkened room an inverted image of the scene outside - the principle of the
camera obscura.
1725 - Johann Heinrich Schultze of Germany discovered that silver salts darken
according to the strength of light to which they are exposed-the basic principle of
all photographic films today.
1827 - Joseph Nicephore Niepce, a retired French army officer,took the first
photographic image. (Exposure time was 8 hours, emulsion was bitumen of
Jedea.)
1839 - Louis Daguerre a French stage designer announced his direct photographic
process. Daguerre had discovered that mercury vapors could bring out an image
on a silver plate and that sodium thiosulfate ("hypo") could fix the image and
make it permanent.
1939 - William Henry Fox Talbot describes a system of imaging on silver chloride paper
using a fixative solution of sodium chloride. Talbot later found that the latent
image could be developed in a solution of gallic acid, and he was the
first person to employ a negative/positive process "Calotype" laying the
groundwork for modern photography.
1830s - Invention of the stereoscope by the Germans. The device was used during the
Victorian era for amusement.

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1849 -The first actual experiments in using photogrammetry for topographic mapping
under the direction of Colonel Laussedaff of the French Army Corps of
Engineers. He experimented on the use of kites and balloons for taking aerial
photographs.
1855 - Scottish physicist James Clark Maxwell, postulates the color additive theory for
the production of color photographs.
1858 - First known aerial photograph is taken from a captive balloon from an altitude of
1,200 feet over Paris by Gaspar Felix Tournachon Nadar.
1861 - With the help of photographer Thomas Sutton, Maxwell demonstrates his
techniques using a bow of multicolored ribbon. (Red filter - sulfo-cyanice of iron,
blue filter - ammoniacal sulfate of copper, green filter - copper chloride, a fourth
filter of lemon-colored glass was also used.)
1860s - Use of aerial observations from captive balloons in American War. Balloons
used to map forest in 1862 not aerial photo though.
1870s - Pictures taken from greater heights, 33,000-34,000 feet, from free balloons.

1873 - Herman Vogel found that by soaking silver halide emulsions (which are naturally
sensitive to only blue light) in various dyes, he could extend their sensitivity to
longer and longer wavelengths, paving the way for photography in the near
infrared.
1899 - George Eastman produced a nitrocellulose-based film which retained the clarity
of the glass plates which had been used to that time.
1903 - Julius Neubronne patents breast mounted camera for pigeons.

1906 - Albert Maul takes first aerial photograph using a rocket propelled by compressed
air which rose to a height of 2,600 feet and took pictures and then parachuted the
camera back to earth.
1909 - Wilbur Wright takes first aerial photograph from an airplane of Centrocelli, Italy.
1915 - Cameras especially built for aerial use are being produced. Lt. Col. J.T.C. More
Brabazon designed and produced the first practical aerial camera in collaboration
with Thornton Pickard Ltd.
1924 - Mannes and Godousky patent the first of their work on multi-layer film which led
to the marketing of Kodachrome in 1935.
1931 - Stevens development of an IR sensitive film (B&W).

1934 - American Society of Photogrammetry founded. Photogrammetric Engineering is

first published. This journal of the American Society of Photogrammetry was later
renamed Photogrammetric Engineering and Remote Sensing. The Society is
now named the American Society of Photogrammetry and Remote Sensing.
1941-1945 - WWII brings about the development of more sophisticated techniques in
aerial photographic interpretation (API). American, British and Germans all
produce promising TIR devices.
1942 - Kodak patents first false color IR sensitive film.

1946 - First space photographs from V-2 rockets.

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 AERIAL CAMERAS

Aerial cameras are precision built cameras specifically designed to expose a large number of
photographs in rapid succession with the ultimate in geometric fidelity.

Parts of Aerial Cameras

The three basic components or assemblies of a frame aerial cameras are: (1) Camera
magazine, (2) Camera Body, and (3) Lens Cone Assembly

Camera magazine. Houses the reels which hold exposed and unexposed film, and it also
contains the film advancing and film flattening mechanisms.

Camera Body. One piece casting which usually houses the drive mechanism. The drive
mechanism operates the camera through its cycle; the cycle consisting of: (1) advancing the
film, (2) flattening the film, (3) cocking the shutter, and (4) tripping the shutter. Power for the
drive mechanism is most commonly provided by an electric motor.

Lens Cone Assembly. Contains a number of parts and serves several functions. Contained
within this assembly are the lens, filter, and diaphragm. With most mapping cameras, the
lens cone assembly also contains an inner cone, or spider. The spider rigidly supports the
lens assembly and focal plane in a fixed relative position.

Lens. The most important part of an aerial camera. It gathers light rays from the object
space and brings them to focus in the focal plane behind the lens. A lens accomplishes
this function through the principles of refraction. A lens placed in front of the object
gathers a pencil of light rays from each point’s bundle of rays and brings these rays to
focus at a point in a plane on the other side of the lens called the image plane. An
infinite number of image points, focused in the image plane, forms the image of the
entire object.

Unexpo
Take-up
sed film
reel reel

Film flattener Film

Format Opening

Focal
length

Lens
Rear nodal point
Shutter Diaphragm
Front nodal point
Filter Lens

Generalized cross section of an aerial single lens camera

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Types of Aerial Cameras:

1. Single Lens Frame Cameras - used in general for photogrammetric and mapping
purposes. Lens must be of high geometric quality; must expose films in rapid succession a
great number of photographs to exacting specifications; must have short cycling times, fast
lenses, and efficient shutters; and must function under the most extreme weather conditions
and against aircraft vibrations. Lens is held fixed relative to the focal plane. The entire
format is exposed simultaneously with a single click of the shutter.

2.Multilens Frame Cameras - Multilens frame cameras have the basic characteristics of
single lens cameras except that they have two or more lenses and expose two or more
pictures simultaneously.

3. Strip Cameras - Strip cameras expose a continuous photograph of a strip of terrain

beneath the path of the aircraft.

4. Panoramic cameras - narrow angular field thru a narrow slit. Ground areas covered by
rotating a prism in front of the lens. Panoramic cameras photograph a strip of terrain from
horizon to horizon; the strip being transverse to the direction of flight.

Fiducial Marks

Fiducial marks are used to locate the principal point or geometric center of the photograph. The
principal point is defined as the point in the focal plane intersected by the optical axis of the
lens. This point is important in reconstructing the geometry of the photograph.

There are usually four fiducial marks which are used to locate the photographs principal point. In
some instances eight fiducial marks are also used. These marks are exposed onto the negative
during photography and subsequently appear on the printed photographs. Fiducial marks may
be located in the corners of the photograph, in the middle of the sides, or sometimes on both
places.

Lines which are drawn by joining opposite pairs of fiducial

marks intersect at or very near the principal point. Aside
from locating the principal point, line joining opposite fiducial
marks also provides a rectangular coordinate axis system
for the photographs. When this coordinate system is used,
image positions on photographs could be located and
measured.

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Focal Length

The focal length of the camera is defined as the distance between the rear nodal point of the
lens and the focal plane. The focal length is usually fixed for most aerial cameras and its value
is precisely determined by calibration. Some camera lenses may be of variable focal lengths.
Such a type of lens is better known as the “zoom lens” for its ability to zoom in on an object from
far away to a much closer distance. It works by having some of its optical elements movable in
relation to one another, so that the lens can be extended to change its focal length and hence
the size of the image.

The nominal values of focal lengths used are: 90mm (3.5”), 153mm (6”), 210 mm (8.25”), 305
mm (12”), and 760mm (30”). In terms of focal length, camera lenses may be classified as short
focal length (less than 305mm or 12”) or long focal length (greater than 305mm or 12”).

Angular Field of View

Single lens frame cameras are often classified according to their angular field of view. Angular
field of view is the angle  subtended at the rear nodal point of the camera lens by the diagonal
d of the picture format.

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 Where:
= angular field of view
d = diagonal of the picture format
f = focal length of the camera used

Angular field of view may be classified as follows

a. Normal angle (up to 75)

b. Wide angle (75 to 100)
c. Super-wide angle (greater than 100)

The most common frame or format size of aerial mapping cameras is 9 inches (23 cm)
square. For a particular format size, angular field of view increases as focal length decreases.
Short focal lengths yield wider ground coverage. Single lens frame cameras are available in a
variety of focal lengths and the choice will depend on the purpose of the photography. The most
common in use today for mapping photography has a 6 inch (152 mm) focal length and 9
inch(23 cm) square format. Although 3½ in(89 mm) 8¼ in(210mm) and 12 in(305 mm) focal
lengths with 9 in formats are also used.

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ANGULAR FIELD OF VIEW PROBLEM. Determine the angular field of view of a camera
having a 23 cm square format and focal length of

a.) 88 mm
b.) 153 mm
c.) 305 mm

Also identify if the camera lens used is normal angle, wide angle, or super wide angle.

SOLUTION:

The camera lens used is super wide angle since the angular field of view is greater than 100°.

The camera lens used is wide angle since the angular field of view falls between 75° and 100°.

The camera lens used is normal angle since the angular field of view is less than 75°.