Which term is used for a marker in a photograph indicating the geometric center or principal point?

Which term is used for a marker in a photograph indicating the geometric center or principal point?

• A. Spot height
• B. Principal Point
• C. Isogonic
• D. Fiducial Mark

Answer: (D)

Fiducial marks are the precise reference markers placed on an aerial photograph or film frame to provide known locations in the image space. They serve as calibration references for photogrammetric measurements, helping to identify where the image’s principal point sits and to establish interior orientation and scale. The term describes the physical markers themselves, not the concept of the image center. Spot height relates to elevation on maps, isogonic pertains to magnetic variation, and the principal point is the geometric center concept—not a marker.

Fiducial marks are the precise reference markers placed on an aerial photograph or film frame to provide known locations in the image space. They serve as calibration references for photogrammetric measurements, helping to identify where the image’s principal point sits and to establish interior orientation and scale. The term describes the physical markers themselves, not the concept of the image center. Spot height relates to elevation on maps, isogonic pertains to magnetic variation, and the principal point is the geometric center concept—not a marker.