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I am calculating WGS84 coordinates of points in an aerial image, given the WGS84 coordinates of the center of the image and the ground distance width and height (calculated from altitude and lens field of view). Images cover a ground area of no more than 150x100m. Thus far, I have neglected the effects of any coordinate system, and linearly calculated coordinates from the center coordinate.

Some inaccuracy in the coordinates has been noticed, particularly near the edges of images, and I am wondering if my neglect of coordinate system and projection is at fault. If I were to take it into account, what "projection" would my images be in? Could I simply convert to UTM Zone X for the computation, and convert the final result back to WGS84, or is UTM not an accurate representation of an image either?

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Are your aerial images orthorectified?satimagingcorp.com/svc/orthorectification.html –  Mapperz Jan 9 '13 at 17:19
    
Ah, I forgot to mention this. No post-processing orthorectification is done, however the camera always points directly at the ground, and the ground is flat, so none is necessary. –  prattmic Jan 9 '13 at 17:22
    
what about the distortion in the camera lens? –  Mapperz Jan 9 '13 at 17:28
    
That could have an effect. It is not taken into account. It is something we have not yet measured. –  prattmic Jan 9 '13 at 17:29
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adjusted for topographic relief, lens distortion, and camera tilt. en.wikipedia.org/wiki/Orthophoto –  Mapperz Jan 9 '13 at 17:30

1 Answer 1

A good guide and illustration into the process of Aerial Photography and Calibrating them to be correctly orthorectified

http://www.nrcan.gc.ca/earth-sciences/products-services/satellite-photography-imagery/aerial-photos/about-aerial-photography/891

Fiducial marks: small registration marks exposed on the edges of a photograph. The distances between fiducial marks are precisely measured when a camera is calibrated, and this information is used by cartographers when compiling a topographic map.

Overlap: is the amount by which one photograph includes the area covered by another photograph, and is expressed as a percentage. The photo survey is designed to acquire 60 per cent forward overlap (between photos along the same flight line) and 30 per cent lateral overlap (between photos on adjacent flight lines).

(and remember aircraft pitch and roll even when weather conditions are perfect for flying for aerial imagery capture.) Some new high tech planes take lidar at the exact same time as the digital photo - which can be used to correct some errors.

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