national aerial resources :: glossary of terms

some helpful terms

block coverage
A group of photos covering a large geographic area or feature.
color infrared photo (cir)
CIR film is manufactured in a way that makes it more sensitive to the near-infrared portion of the spectrum. On a CIR photo, infrared energy reflected by vegetation is represented by tones of red; water is represented by black. It is most commonly used for vegetation studies.
color photos
Aerial photographs produced in color are less common and more expensive but can be more useful because the human eye can discriminate between color variations better than shades of gray.
contact print
A photograph produced directly from a negative of the same size, usually 9"x9".
diapositive
A transparent positive image on plastic-based film used for creating topographic maps.
diazo or blue line
An aerial photo copied to paper by a process similar to blueprint production. The image usually appears in shades of blue but can be black and white. Diazo prints are normally available in large formats; scale may vary from 1"=400' to 1"=800'.
digital print
A computer reproduction of a contact print. The scale can be changed to meet most needs.
large scale vs. small scale
A large scale (example: 1"=1000") implies that the ground features are larger as opposed to larger coverage area. A small scale (example: 1"= 5000') implies a larger coverage area but lacks the detail of a large-scale photo.
mosaic
A series of overlapping aerial photos that form a composite image of a larger area.
oblique photos
These photos are taken with the camera axis at an angle other than 90° to the ground. The image can be a high oblique, which includes a horizon, or a low oblique, which does not.
orthophoto
A reconstructed aerial photo in which all distortion has been removed. See rectification.
orthophoto mosaic
A mosaic constucted from orthophotos. The image is seamless because the scale variations and distortions have been removed.
photo mosaic index
A mosaic used to reference individual aerial photos by flight line and frame number.
rectification
A process that removes most scale variations and distortions from aerial photos in order to produce orthophotos.
spot coverage
Spot coverage is high altitude photography covering a large geographic area or feature.
stereopair
Two adjacent, overlapping aerial photos that when viewed together through a stereoscope produce a 3D image.
vertical photos (required for stereo)
These are the most common type of aerial photograph. They are produced with the camera axis aimed vertically, perpendicular to the ground.

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