Science & Technology in Action

4th Edition

Optical Imaging (Aerial Photography)

Ordnance Survey Ireland

By using a combination of aerial photography, laser detection and ranging (LIDAR) and GPS virtual three dimensional landscapes can be generated. Terrain can be viewed from various angles and stereoscopic images can be produced.
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Lesson excerpt

In the 1820s–1830s different systems of photography were invented. In 1858 Gasper Felix Tournachon took aerialphotographs of Paris from a balloon. In 1889 Arthur Batut was the first to use a kite for photography and not long after the development of powered flight aeroplanes were similarly used (1908).

Yhere have been many developments in aerial imaging over the last hundred and fifty years including stereoscopy, colourphotography, tele-photo lenses, auto-focus, auto-exposure,infrared, laser, digital imaging, radar and GPS. In this lesson we will look at the principles of optical imaging and how they are applied in surveying.

Images formed by lenses
If you look closely at a hanging drop of water you may observe in it a small inverted image of the surroundings. A sphere of glassproduces the effect more strikingly. A convex lens, which can be considered to be a slice of a sphere, can be used to form images on a flat surface such as a wall or a screen; this would more correctly be called a plano-convex lens.

If a magnifying glass is held some distance from a smooth white wall an inverted image of the surroundings will be projected onto the wall. The distance at which this happens depends mainly on the curvature of the lens but also on the distance to objects in the vicinity. Objects at different distances from the lens cannot be ‘in focus’ at the same time. The minimum distance at which an image can be formed is called the focal length of the lens; this occurs when the object being imaged is far away (‘at infinity’).

True or False?

  1. In 1858 Gasper Felix Tournachon took aerial photographs of Paris from a small aeroplane.
  2. Stereoscopic images produce an illusion of three dimensions.
  3. A convex lens can be used to form an image on a screen or on photographic film.
  4. A simple lens has the same focal length for all colours.
  5. Global positioning handsets calculate positions by measuring the time difference between radio signals from a number of satellites.
  6. The proportion between the sides of a triangle does not change if it is magnified.
  7. If two triangles have the same angles then their corresponding sides are directly proportional to one another.
  8. All prisms have triangular ends.