Vertical Aerial PhotographCharacteristics• tilt ≤ 3° from the vertical• scale is approximately constant throughout the photo• p=i=n• within limitations, a vertical air photo can be used as a map substitute• most common format is a 9 by 9 inch photograph
Vertical Aerial PhotographNegative plane f (focal length) = C (principal distance) O f=CPositive plane Hmge (flying height) p=i=n Mean ground elevation
Fiducial Marks• optically projected geometric figures located at either the four corners of a photograph, or on the four sides of a photograph• define the coordinate axes and geometric center of a single aerial photograph• Intersection represents the principal point of the photograph
Three Photo Centers1. Principal Point – geometric center of the photograph; intersection of the line normal to the image plane through the PC2. Nadir – point vertically below the camera at the time the photo was taken; intersection of the plumb line through the PC with the image plane3. Isocenter – point halfway between the principal point and nadir; point intersected by the bisector of the angle between plumb line and optical axis
Three Photo Centers Ground PPoint Isocenter Nadir
Kinds of Photography or camera according to focal length (f)• Wide-angle (f = 6 inches)• Normal-angle (f = 12 inches)• Superwide-angle (f = 3.5 inches)
Photoscale of Vertical PhotoRecall: distance on photo f photoscale distance on ground HBut what if not all the required values are given initially, and instead some other parameters are known?
Determining PhotoscalePhotoscale may also be determined according to:• Smallest detail and resolution• C-factor and desired minimum contour interval• Expected accuracy• Enlargement from photo to map in the instrument
Smallest detail and resolution• Resolution – smallest distance that a feature on the ground is still discernible on the image/photo 1 resolution photoscale s p smallest detail
Smallest detail and resolutionExample: The smallest detail that needs to be seen on the photograph is 1 foot in length. If the resolution of the photo is 0.1 mm, determine the photoscale.
Smallest detail and resolutionSolution: 1 photoscale 3000
C-factor and desired minimum contour interval• Contour interval – difference in elevation between consecutive contour lines flying height H C factor contour interval h• C-factor range from 1200 to 1500
C-factor and desired minimum contour intervalExample: The C-factor of the instrument is given to be 1500. If the desired contour interval is 1 meter, determine the photoscale.
Enlargement from photo to map• Using the stereoplotter, there will be an enlargement from the photo to the stereomodel: Z enlargement Cwhere: Z = projection distance for stereoplotter C = f = projection distance of camera
Enlargement from photo to mapExample: A map with scale 1:5000 was derived from a stereomodel with a scale of 1:8000, using a stereoplotter. The projection distance of the stereoplotter is twice the focal length of the camera. Determine the scale of the photograph that was used to generate the stereomodel.
Enlargement from photo to mapSolution: 1 photoscale 16000