Calculating an angle from a picture

The basic formula to calculate an angle (like altitude or azimuth) from a picture (photometry method), is:

Angle = arctan (Difference / Size picture * Size  recording / (Focal length * (1 + Magnification))

Magnification = 'distance from rear principal point to recording (picture) plane' / 'distance from front principal point to subject (object)'
(can be assumed zero in the case when one takes no macro exposures).

Remark: make sure no barrel of pincushion distortion is present in the picture (SLR cameras tend to have less of this, because of proper optics).

Calculating the angle

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Recording equipment parameters

Focal length:   [mm] 
Size recording: 35 mm 
Magnification:  [-] (0 is normal for non fish-eye/macro lenses)

Picture parameters

Along picture side:  horizontal side (azimuth)  vertical side (altitude)
Size picture side:  [pixels], [mm], etc.
Start point of angle:  [pixels], [mm], etc.
End point of angle:  [pixels], [mm], etc.

angle:  [°]
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Last content related changes: Aug. 11, 2000