# Inner and outer orientation

In the case of a photogrammetric image recording, the orientation data describe the position of the projection center of the camera relative to the image plane (internal orientation) and the position of the projection center and the recording direction relative to the recording object (external orientation).

Using this data, the recording situation and thus the photogrammetric beam of the central perspective image can be reconstructed geometrically. The image data can thus be used for metrological purposes.

## Inner orientation

Inner orientation

The internal orientation of a measuring camera describes the position of the projection center in relation to the image plane through the three coordinates , and . ${\ displaystyle O}$${\ displaystyle X '}$${\ displaystyle Y '}$${\ displaystyle C_ {k}}$

${\ displaystyle X '}$and ( instead of terrestrial recordings ) are the coordinates of the main point of the image . This is the base point of the perpendicular through the projection center (and not the point of penetration of the optical axis through the sensor plane). The coordinate system is spanned by two straight lines through the image marks or the image corners. The straight lines intersect in the center of the image . ${\ displaystyle Y '}$${\ displaystyle Z '}$${\ displaystyle Y '}$ ${\ displaystyle H '}$${\ displaystyle O}$${\ displaystyle M '}$

The third variable is the chamber constant (also: camera constant) , the distance between the projection center and its plumb point . The chamber constant can also be understood as the focal length of the lens used. In electronic cameras, the image plane is represented by the sensor chip instead of the film. ${\ displaystyle C_ {k}}$${\ displaystyle O}$${\ displaystyle H '}$

The amounts of and should be as small as possible, i.e. the main point of the image should coincide with the center of the image. ${\ displaystyle x '_ {H'}}$${\ displaystyle y '_ {H'}}$

Occasionally, data for the correction of imaging errors in the objective are also counted among the parameters of the internal orientation. A suitable mapping rule z. B. of the type determined a corrected image coordinate for each point . ${\ displaystyle x '' = Ax '}$${\ displaystyle (x ', y')}$${\ displaystyle (x '', y '')}$

## External orientation

External orientation

The external orientation of a photogrammetric recording describes the location and position of the camera during the recording in relation to the subject itself. The position (translational component) is described by the three coordinates of the projection center . In the case of an aerial photograph, these would be the coordinates of the nadir point in the geodetic system and the altitude above the reference area. The position (rotary component) is determined by three independent angles of rotation, e.g. B. Azimuth , tilt and cant . In the case of vertical shots, the ratio (chamber constant to flight height) indicates the image scale. ${\ displaystyle (x, y, z)}$${\ displaystyle O}$${\ displaystyle N}$${\ displaystyle h}$${\ displaystyle \ mathbf {\ alpha}}$${\ displaystyle \ mathbf {\ nu}}$${\ displaystyle \ mathbf {\ kappa}}$${\ displaystyle C_ {k} \,: \, h}$

The external orientation is often determined in image flight through the use of GPS and INS .

## literature

• Karl Kraus: Photogrammetrie, Volume 1, Geometric information from photographs and laser scanner recordings . 7th edition, Walter de Gruyter Verlag, Berlin 2004, ISBN 3-11-017708-0 .
• Jürgen Bollmann (ed.): Lexicon of cartography and geomatics . Spektrum Akademischer Verlag, Heidelberg 2002, ISBN 3-8274-1056-8 .

## Individual evidence

1. Luhmann, Thomas: Close-range photogrammetry basics, methods and applications . 3., completely reworked. and exp. Wichmann, Berlin 2010, ISBN 978-3-87907-479-2 .