Aerial Photogrammetry 1c1c40

Aerial Photogrammetry By PGRNI Pussella

Definition • Photogrammetry is defined as the art , science and technology of obtaining reliable information about physical objects and the environment through a process of recording, measuring and interpretation of photographic images. • The science of photo analysis

Photogrammetry & Remote Sensing • „The art, science and technique to obtain reliable geometric and thematic information on the earth and its physical environment by acquisition, measurement and interpretation of images, which are obtained by remote sensing sensor systems“

Introduction • Traditional application – Extracting topographic information from aerial photographs • Present – To process satellite images for topographic and non topographic information of the terrain. • Introduced in 1851

Introduction Objective is… Inverse the process of photography (i.e. reconstruction of the object space from image space). Results can be, Coordinates of the required object points, Topographical/Thematic maps 1/7/2015

Photogrammetry & Related Discipline Term ‘PHOTOGRAMMETRY’ was derived from Greek words Photos : Light Graphem :To engrave, write or record Metrein : To measure ‘Light engrave data measuring’ The most important factor is, that the objects are measured without being touched. Hence, in broader sense; including all disciplines, the term ‘Remote Sensing’ can be used to describe the Photogrammetry. 1/7/2015

Photogrammetry & Related Discipline Other Branches of photography used in the science of photogrammetry: • Space Photogrammetry: If the camera is fixed in space. It may be mounted in a satellite, or positioned on the moon or a planet. • Close-range Photogrammetry: If the camera is kept quite close to the object to obtain the detailed information about object. 1/7/2015

Photogrammetry & Related Discipline Aerial photogrammetry is mainly used to produce • topographical or thematical maps and • digital terrain models. But, Photogrammetry alone cannot produce a map. Why? All details cannot be seen in the photographs.

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Advantages • • • • • • • •

Bird’s eye view of the ground Analog to the human eye system High resolution High information density Multidisciplinary applications Permanent records Low cost Time saving

Limitations • Effects of atmospheric conditions • Spectral sensitivity limited • Loss of film

Introduction Why use Photogrammetry ?...... Special Application Areas • Archeology

• Cultural heritage • Close-Range Photogrammetry –Architecture, Industry • Police (accidents, forensic medicine) • Medicine • Biometry • Extraterrestrial, star-camera, astronomy 1/7/2015

Later, developed stereo viewing instruments were used to produce topo-maps from near vertical photographs. • In 1930, Analogue stereo plotters. • In 1958, Analytical stereo plotters • Since 1980, Digital Photgrammetry with increasing automation GPS flights. Digital workstations • In 2000, Digital large format cameras.e.g. ADS40, DMC 1/7/2015

Histroic Review Analogue Film Cameras:

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Histroic Review Metric Aerial Film Cameras:

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Histroic Review Elements of a metric aerial film camera

 Camera body with lens (nozzle)  Film cassette  Camera mount (stabilized)  Navigation system (telescope and overlap control device) TODAY:  Connection to GPS [and INS]  Flight planning computer 1/7/2015

Aerial Photography Single point perspective view of the earth surface called Aerial Photograph. Infinite number of rays go through camera one point: perspective centre, it make geometric model.

Aerial Photography Basic Concepts of Aerial Photography: Film: most air photo missions are flown using black and white film, however color, infrared, and false-color infrared film are sometimes used for special projects. Focal length: the distance from the middle of the camera lens to the focal plane (i.e. the film). As focal length increases, image distortion decreases. The focal length is precisely measured when the camera is calibrated. Scale: the ratio of the distance between two points on a photo to the actual distance between the same two points on the ground.

Aerial Photography Basic Concepts of Aerial Photography:

Aerial Photography Can you used aerial photograph as a map directly?  Aerial photographs are simple point perspective views of the earth surface where as maps are orthogonal representation of all surface.  Size, shape and position of objects are distorted in aerial photographs. However, aerial photographs can be used to reconstruct maps and to accurately measure distances and heights.

Aerial Photography • If the terrain is completely flat and horizontal, then the photograph can be used as a map. • If difference heights occur, then objects are displace from their location. • Aerial photograph can not used as a map.

Aerial Photography What is a Map?

• Map can be consider as an orthogonal projection of the terrain to a horizontal plane at a reduce scale. • But photograph produces a perspective image of a central projection of the terrain surface.

How to prepare maps from Aerial Photographs? • To overcome relief distortion, two photographs are taken of the same area at different positions.

• These photographs are overlapped and can be used to see stereo model. • Using this principal, a map can be prepared.

Types of Aerial Photographs • Aerial photography most commonly divided into two major types, the vertical and the oblique. • Each type depends upon the attitude of the camera with respect to the earth's surface when the photograph is taken. Vertical or Near Vertical Photography • Camera axis is < 3° from vertical Oblique Photography • Camera axis is > 3° from vertical • Low oblique—no horizon • High oblique—includes horizon

Property of an Aerial Photographs Fiducials: permanent reference points exposed onto the photograph. Principal Point (PP): Center of photo—found by intersection of lines drawn between opposing fiducials.

Nadir: image of point directly below airplane at time of photo (Nadir will equal PP for vertical photos).

Property of an Aerial Photographs • Photo sizes – 18cm× 18cm – 23cm× 23cm • • • •

Fiducial marks Position of the bubble Barometer information Calibration information – Principle distance