[Talk-GB] Aerial Photography

Chris Hill osm at raggedred.net
Mon Sep 14 18:30:20 BST 2009

Peter Miller wrote:
> I get the impression that rectification gets a lot harder as the angle 
> gets more slight and it is clear to me that a camera pointing straight 
> down would be the most useful device going forward.
Not easy to do.  You can't legally modify an aircraft at all without 
invalidating its certificate of airworthiness, so where to mount the 
> The time of day is also important to avoid long shadows.
Generally an overcast day reduces the contrast to make the photos easier 
to use, but shadows can actually be very helpful.  They give an 
impression of height for some things.  For archeology shadows sometimes 
showed medieval ridge and furrow field systems and the edges of roman 
building platforms.  Winter time when there are no leaves on the trees 
will reveal much more detail.  The true route of roads and streams are 
easily hidden by tree cover from the air.  Calm winter days often are 
less turbulent than summer days so the 'plane as a platform is 
steadier.  (Clear blue skies in summer can be VERY bumpy in the air).
> I am pleased that this project is creating some useful discussion 
> which we should continue to see what we can extract from these images 
> and what we can learn going forward.
> Tools to process images and to host rectified images seem to be pretty 
> crucial to take full advantage of all this.
> Fyi, I have added comments to some images to say what it is of, the 
> bearing the image was taken at, and the appropriate link to OSM.

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