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# What to specify for the interior orientation within a digital camera model?

by on ‎12-06-2016 05:30 AM (1,015 Views)

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## Question

What needs to be specified for the interior orientation within a digital camera model?

Interior orientation defines the internal geometry of a camera or sensor, as it existed at the time of capture. The internal geometry of a camera is defined by specifying the following variables:

• Principal point
• Focal length
• Fiducial marks
• Lens distortion

When using frame cameras, measuring fiducial marks establishes the position of the principal point, i.e., the origin of the image coordinate system. However, when using digital, video or non-metric cameras, interior orientation involves defining the x and y pixel size of the camera Charge Coupled Device (CCD) or scanning resolution used to digitize the film obtained from a camera not using a CCD. The pixel size of the CCD has to be defined in microns. Generally the size of the complete CCD in pixels and in millimeters is known. With this information it is possible to calculate the size of one pixel in microns.

Below is an example on how to calculate the pixel size in x and y direction in microns:

Size of the CCD array in pixel: 2036 x 3060 pixels
Size of the CCD array in mm: 18.4 mm x 27.6 mm

In order to find out what the x and y pixel size of one pixel in microns is it is necessary to do the following:

18.4 mm / 2036 pixel = 0.0090373 mm x 1000 = 9.0373 microns
27.6 mm / 3060 pixel = 0.0090196 mm x 1000 = 9.0196 microns

Pixel size in x direction (microns): 9.0373
Pixel size in y direction (microns): 9.0196

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