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
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5. Photogrammetry
Derived from 3 Greek words
– photos – light
– gramma - something drawn or written
– metron - to measure
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 verticallybeneath the center ofthe camera
lensduringexposure
Photographic nadir
intersection of the photograph and the vertical line that
intersects the ground nadir andthe center ofthe lens
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).
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Terrestrial photogrammetry (mostly close range
photogrammetry)
Branch of photogrammetry wherein photographs are
taken from a fixed position on or near the ground
Aerial photogrammetry (mostly far range
photogrammetry)
Photographs are taken by a camera mounted in an
aircraft flying over the area
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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
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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
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.
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●
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.
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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
• Similarto planetable surveying.
• If the directions of the same objects photographed from two extremities of
measuredbaseare knowntheir position canbe located bythe intersection oftwo
raysto the sameobject
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
36. Photo Theodolite
The instrument consists of a photographic camera with an internal
compasscard, housedin analuminumbox with a horizontal circle below,
and atransit-mounted telescope with vertical arc above. The horizontal
circle isgraduated 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.
