[OSM-talk] Aerial imagery [was Yahoo and OSM]

David Earl david at frankieandshadow.com
Fri Mar 30 15:52:36 BST 2007


> Good aerial imagery is taken using markers placed at predefined ground
> locations _plus_ a very good GPS _plus_ gyroscopes that allow you to
> determine the pitch and bank angle of the aircraft. Additionally you
> should have a radar altimeter that allows you not only to determine the
> displacement of images against GPS location that occurs due to pitch
> and bank but also delivers the required altitude information in order
> to correct the deformation that you get by projecting the image onto
> the terrain.

If you're working on virgin territory, perhaps. But mostly I'm using the
satellite images to pick up detail that I can't get easily off the ground
(e.g. factory buildings, lakes). So I've often got a pattern of streets
already.

I suppose it depends on the area covered by each picture, but if I can
identify four known points in a picture from my ground survey, and an editor
offers the ability to align points in the picture with points from my own
surveying, distorting the picture appropriately into a quadrilateral, I
think aerial pictures (indexed by location, which can be a simple GPS
reading) would probably be useful with no calibration at all.

David






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