Photogrammetric Analog Cameras and Frames: Fiducial Marks and Marginal Information on Photos (Especially for GATE-Geospatial 2022)

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Photogrammetric analogue cameras are those cameras in which the image is instantly registered in a photographic film.

Components of Analog Cameras

The three main parts of cameras can be distinguished in the figure and are the following:

  • Store or magazine: It contains the film and its corresponding advance mechanisms and it assures that the film remains flat during exposure.
  • Body: It connects the magazine with the lens assembly.
  • Lens assembly: It stores the optic system, the diaphragm, the shutter, the filters … The intersection of the optic axis with the focal plane indicates the position of the principal point of the image.
Components of a Photogrammetric Analogical Camera

Platform and Frame of Analogue Camera

The cameras are in the plane over a frame that usually allows the correction of the orientation and the levelling of the camera.

The last generations of frames have a stable platform, that registers the spins of the camera during the flight, correcting its verticality and an FMC9 system that reduces its apparent motion and the image blurring, moving the camera towards the back. This FMC is essential the lower the height of the flight is and the greater the speed of the plane is.

Platform of the Camera in the Plane

Analogical cameras have a standard format of 23x23cm, and they contain in their focal plane a frame where the following are represented:

  • Fiducial Marks
  • Marginal Information

Fiducial Marks

Fiducial marks are essential to begin the photogrammetric process with the internal orientation of the photograms. There are, usually, 8 fiducial marks, 4 in the corners and 4 in the central parts. They have exact coordinates in the coordinate system of the image, being this one of the data included in the calibration certificate of the camera. The fiducial centre of the image is defined as the intersection point of the lines that connect the fiducial marks.

Fiducial Marks

The fiducial centre and the main point do not necessarily coincide. This displacement is indicated in the calibration parameters of the camera.

Marginal Information

Marginal information is some information about the name of the project, the responsible organism of the project, the date and time when the picture was taken, the name of the camera, the calibrated focal length, the scale of the photogram, the strip number, the photogram number, the approximate height and the spherical level in some cases.

Example of Analogical Photogram with Fiducial Marks and Marginal Information

Analogical Photogram

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