[Talk-GB] Aerial Photography

Chris Hill osm at raggedred.net
Mon Sep 14 12:37:04 BST 2009

One of the airfields I flew from was a base for the OS photo surveying 
unit.  They had a 'plane which had been modified to have a downward 
pointing, very expensive camera built into the fuselage.  They could 
then fly long straight strips, taking overlapping photos and then taking 
overlapping strips.  The pilots didn't stay long - it was a very 
difficult and tedious job getting the strips to line up.  They flew a 
few in a day, always in the same direction to assist with the way your 
track gets moved by the wind. 

Cheers, Chris

John Robert Peterson wrote:
> Part of the idea of this project was to kick start thinking about this 
> sort of thing.
> The ideal situation for me would be if we could have some automated 
> tool on a sever somewhere receiving images from users, and 
> automatically rectifying them.
> This sounds imposable, but I believe that with a very small amount of 
> user help it could work:
> Images can be automatically pinned together in overlaps (and high res 
> images can be pinned onto wide area images) using tools similar to 
> those in Panorama Tools / hugin (this searches for notable points in 
> the image data, and matches them between images);
> searching the images for road markings (and/or cars) and matching 
> these to the gps traces already uploaded would give a reliable enough 
> way to add real world control points;
> if a concept of altitude is added, automatic control points between 
> images appearing on top of skyscrapers would not be too damaging;
> approximate terrain relief for most of the planet is already known, 
> this can be tied into the above to help;
> manually adding control points would be done by displaying already 
> rectified images next to a map, with the user adding pins to useful 
> points;
> images with no rectification data at all would be added using a push 
> pin system similar to that used on http://warper.geothings.net/
> the above is a pipe dream at the moment, but has the potential to 
> revolutionise how we do things in my opinion.
> Any further ideas on this?
> The images of stratford were taken mostly angled, with a few almost 
> vertical. we spiraled around the town and I took images out the 
> downward facing window, it seemed to work pretty well (if the results 
> are a little chaotic)
> mapping from these images is the million dollar question -- the raw 
> images are going up online at 
> http://www.flickr.com/photos/thingomy/collections/72157622345143470/ 
> and are fine for visual reference while mapping, but rectifying them 
> is a more tricky issue.
> JR
> 2009/9/14 Tristan Thomas <tristan.thomas at wikinewsie.org 
> <mailto:tristan.thomas at wikinewsie.org>>
>     Many of the photos taken above Stratford upon Avon seem to be
>     taken at an angle-how do people find them for mapping from?
>     2009/9/14 Chris Hill <osm at raggedred.net <mailto:osm at raggedred.net>>
>         I used to hold a pilot's licence and I did some work
>         photographing archaeological sites.  Photos taken pointing
>         sideways are much harder to work with than photos pointing
>         straight down. Any kind of rectification adds unwanted
>         artifacts.  I used to make high bank angle turns (60' bank
>         angle) over the feature I wanted to photograph which made it
>         very easy to photograph.
>         I was trying to photograph a small area in detail, so circling
>         over the feature helped.  I was also using film (before
>         widespread hi-res digital), so there was a limited stock of
>         film but the resulting image was the equivalent of about 25mp.
>          To reduce parallax I used a telephoto lens.
>         It gives a very interesting overview, but it's not a patch on
>         surveying on the ground where you have access.
>         Cheers, Chris
>         Tristan Thomas wrote:
>             I would be very interested to hear what people think of
>             this effort.  I'm currently studying to be a pilot & I
>             know that many people who do fly routinely take aerial
>             pictures of the landscape below, especially of towns etc.
>              I know most of them would be more than happy to allow
>             their photos to be used of OSM.  If we could find a way to
>             upload them somewhere, then I'm sure we could dramatically
>             increase the aerial photography we have without having to
>             pay to hire the planes or get it sponsored.  I could just
>             upload them all under one Flickr account for OSMers to
>             look through & do some tracing if they wish, but it
>             doesn't seem the most efficient way to do it?
>              Thoughts?
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