Porro-Koppe principle

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The Porro-Koppe principle (rare photogoniometer ) is a method developed by Carl Koppe at the Technical University of Braunschweig , with which a noticeable increase in the accuracy of the earth image measurement was possible in the early days of photogrammetry .

Instead of determining the objects on the glass plate in a right-angled coordinate system when evaluating the measurement images , their image angles are measured through the lens of the recording chamber. Because the distortions of the measurement image that arise during the recording then have the same effect on the evaluation, some systematic errors can be eliminated.

Instead of the photo lens - which is usually fixed in the camera - you can also use an identical lens for the evaluation.

Technical process

For angle measurement according to the Porro-Koppe principle, the developed negative is placed in a measuring camera, the lens of which corresponds to that of the picture. With the measuring telescope of a theodolite-like instrument, which is focused at infinity, one now aims through the objective at the points to be measured on the illuminated negative. This gives you the same horizontal and elevation angles that you could have measured during the recording.

A prerequisite, however, is a camera lens that is structurally identical in detail and the use of an analactic telescope (see Ignazio Porro ), the focus of which must be exactly above the vertical axis of the theodolite.

The method was particularly useful in the early days of image measurement because the camera lenses of the time still had relatively large distortions. With modern lenses, these image errors are only on the order of a few micrometers (2-10 µm) and are generally taken into account in calculations.

See also

literature

  • International Congress of Photogrammetry: International Archives of Photogrammetry , Volume 21, Part 5. Board of the International Congress of Photogrammetry, 1976
  • German Society for Photogrammetry: Image measurement and aerial photography . H. Wichmann, 1976. p. 79
  • Franz Ackerl : Geodesy and photogrammetry , 1st part: Instruments and methods of measurement , p.76, 361f (chapter 35, The perspective of the measurement image ) and 429. Verlag Georg Fromme & Co., Vienna 1950

Web links

Individual evidence

  1. ↑ Koppe also developed the first photo theodolite
  2. ↑ Until around 1950 people worked almost exclusively with photo plates instead of films, and the original was just a negative on the glass plate
  3. ↑ Porro achieved this by installing a converging lens between the telescope objective and the crosshair . The beam path corresponds to that of a Huygens eyepiece