Photogrammetry is the science of obtaining reliable information about physical objects through analyzing photographic images. It involves recording, measuring, and interpreting photographs and electromagnetic radiation. There are two main types: aerial photogrammetry which uses photographs taken from aircraft, and terrestrial photogrammetry which uses ground-based photos. Photogrammetry is used to produce topographic maps and digital terrain models for purposes like architecture, engineering, archaeology and more.

1. Module III
Photogrammetry

2. Photogrammetry
Photogrammetry is the art, science, and
technology of obtaining reliable information
about physical objects and the environment
through processes of recording, measuring,
and interpreting photographic images and
patterns of Electromagnetic radiant energy
and other phenomena

5. Photogrammetry
Derived from 3 Greek words
– photos – light
– gramma - something drawn or written
– metron - to measure

6. camera principle

7. camera principle

8. Definitions
Camera axis Line passing through the centre of the
camera lens perpendicular both to the camera plate
(negative) and the picture plane (photograph)
Picture plane Plane perpendicular to the camera axis at
the focal distance in front of the lens.
Principal point Intersection of camera axis with either
the picture plane (positive) or the camera plate (negative)
Focal length Perpendicular distance from the centre of
camera lens to either the picture plane or the camera plate

9. Definitions
Focal plane (image plane) plane (perpendicular to the
axis of the lens) in which images of points in the object
space of the lens are focused
Perspective Centre Every light ray, which reached the
film surface during exposure, passed through the camera
lens (which is mathematically considered as a single
point, the so called “perspective center”)
A photographic image is thus a “central perspective”.

10. Basic elements
 Fiducial marks
Marks at the edges and corners recorded during
exposure
 Principal point
Point of intersection of lines connecting opposite
pairs of fiducial marks

11. Basic Elements
Ground nadir
point on the ground vertically beneath the center of the
camera lens during exposure
Photographic nadir
intersection of the photograph and the vertical line that
intersects the ground nadir and the center of the lens

12. Date of
Photography
Principal
Point
Nadir Point
Mission ID
Frame
Number
Fiducial
Marks

13. Principally, photogrammetry can be divided
into:
1. Depending on the lens-setting:
• Far range photogrammetry (with camera distance
setting to indefinite), and
• Close range photogrammetry (with camera distance
settings to finite values).

15. • Terrestrial photogrammetry (Terrestrial photogrammetry (mostly close range
photogrammetry)
Branch of photogrammetry wherein photographs are taken
from a fixed position on or near the ground
• Aerial photogrammetry (Aerial photogrammetry (mostly far range
photogrammetry)
Photographs are taken by a camera mounted in an aircraft
flying over the area
2. Another grouping can be

17.  Oblique photographs
- Cameras oriented toward the side of the aircraft
-
 Vertical photographs
- camera aimed directly at the ground
surface from above
- difficult to recognize ground features but
measurements can be made

20. Vertical aerial photograph
an aerial photograph is considered vertical only if the
isocenter, nadir and the principal point are in perfect
alignment
Orthophoto
a digital image derived from aerial photography where all
distortions and displacements have been removed
photogrammetrically

24. Oblique photographs

26. Advantages
An aerial photograph has the following advantages over a map:
1. It provides a current pictorial view of the ground that no map
can equal.
2. It is more readily obtained. The photograph may be in the
hands of the user within a few hours after it is taken; a map
may take months to prepare.
3. It may be made for places that are inaccessible to ground
soldiers.
4. It shows military features that do not appear on maps.
5. It can provide a day-to-day comparison of selected areas,
permitting evaluations to be made of enemy activity.
6. It provides a permanent and objective record of the day-to-day
changes with the area.

27. Disadvantages
The aerial photograph has the following disadvantages as
compared to a map:
1. Ground features are difficult to identify or interpret without
symbols and are often obscured by other ground detail as,
for example, buildings in wooded areas.
2. Position location and scale are only approximate.
3. Detailed variations in the terrain features are not readily
apparent without overlapping photography and a
stereoscopic viewing instrument.
4. Because of a lack of contrasting colors and tone, a
photograph is difficult to use in poor light.
5. It lacks marginal data.
6. It requires more training to interpret than a map.

28. Uses and Users
Aerial photogrammetry is mainly used to produce
topographical or thematical maps and digital terrain
models.
Among the users of close-range photogrammetry are
architects and civil engineers (to supervise buildings,
document their current state, deformations or
damages), archaeologists,

29. Advantages of vertical over oblique aerial photographs
 Vertical photographs present approximately uniform scale
 The determination of directions (i.e., bearing or azimuth) can
be performed in the same manner as a map.
 Vertical photographs are easier to interpret than oblique
photographs.
 tall objects (e.g., buildings, trees, hills, etc.) will not mask
other objects as much as they would on oblique photos.
 simple to use photogrammetrically as a minimum of
mathematical correction is required.
 To some extent and under certain conditions (e.g., flat
terrain), a vertical aerial photograph may be used as a map if
a coordinate grid system and legend information are added.
 Stereoscopic study is also more effective on vertical than on
oblique photographs.

30. Advantages of oblique over vertical aerial photographs
 covers more ground area than a vertical photo taken from
the same altitude and with the same focal length.
 If an area is frequently covered by cloud layer
 Oblique photos have a more natural view
 Objects that are under trees or under other tall objects may
not be visible on vertical photos if they are viewed from
above.
 Determination of feature elevations is more accurate using
oblique photograph than vertical aerial photographs.
 oblique aerial photos are not used for photogrammetric and
precision purposes, they may use inexpensive cameras.

31. Terrestrial Photogrammetry
Basic Principles
Similar to plane table surveying.
If the directions of the same objects photographed from two
extremities of measured base are known their position can be
located by the intersection of two rays to the same object

32. 20° 20°20° 20°10°10°10° 10°
0°0°
Direction of pointings in terrestrial photogrammetry
S1 S2

33. Terrestrial Photogrammetry
classifications
Plane table photogrammetry
Consists essentially in taking a photograph of the area to be mapped from each of the two or
three stations.
Terrestrial stereophotogrammetry
The camera base and the angles of intersection of the datum rays to the points to be measured
can be considerably reduced since the camera axes at two stations exhibit great similarity at
two stations.
The image points which are parallactically displaced relative to each other in the two
photographs are fused to a single spatial image by the stereoscopic measurement

35. Photo Theodolite
a combination of a theodolite and a terrestrial camera

36. Photo Theodolite
The instrument consists of a photographic camera with an
internal compass card, housed in an aluminum box with a
horizontal circle below, and a transit-mounted telescope with
vertical arc above. The horizontal circle is graduated to 30
minutes, and read by vernier to single minutes. The vertical
arc extends 90 degrees either way, and is graduated to 30
minutes and read by vernier and small telescope to single
minutes. The whole instrument sits on a tribach base, suitable
for mounting on a tripod.

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