[Talk-ca] Aerial images
ve6srv at gmail.com
Wed Jan 9 21:21:00 GMT 2013
On Wed, Jan 9, 2013 at 12:27 PM, Colin McGregor <colin.mc151 at gmail.com> wrote:
> Has anyone here looked closely at Public Laboratory's balloon kit
> (http://publiclaboratory.org/home) or other sources for getting good
> high resolution aerial images? Reason I ask is that Toronto is well
> served by quality aerial images, but some of the spots outside Toronto
> (that I am interested in) are very poorly served, and well, I was
> wondering if anyone had hands on experience with some of this stuff?
I've flown a number of high altitude balloon projects, with digital
cameras on board. These are free floaters headed to >100,000 ft, not
tethered balloons. We have cameras on board taking images that could
be used for this type of work.
I have not tried stitching images together to georeferenced locations yet.
One of the concerns I have is the distortion involved, and parallax
errors. You need to fly fairly high in order to get a good shot
looking down, and require a decent resolution camera to gather enough
detail. You can set the camera for a medium level zoom to get higher
resolution, but you get smaller areas in the image.
Another issue is ensuring that you are not flying a payload that
endangers air traffic. There are rules governing the maximum size of a
balloon, the maximum payload weight, maximum strength of the tether
line, and maximum altitude before you get into controlled airspace.
For our free flying balloons, we have to stay below 115 cu ft of gas,
and due to that limit, we can only lift about 4 lbs of payload. You
can get some pretty decent cameras with time lapse timers which are
pretty light. If your tether breaks, say goodbye to your camera. If
your balloon bursts, you'll want a parachute. You probably don't want
to drape the tether over power lines either. Lift gas is also a
concern. Helium is in short suppply, and if you do manage to find
someone who will sell to you as a new customer (good luck), you'll be
paying an awful lot. A K tank is probably over $300 now. You can fly
hydrogen with a tank costing about $60, but you need to observe good
safety precautions due to the flammability issue.
Now, given all that, you can still get out there and play...
Another option to look at is flying a kite. You don't have to buy the
expensive balloon and lift gas, but you do have to have sufficient
wind. Search Google for Kite Aerial Photography. There's lots of links
out there. You can achieve the same with a kite as you can with the
Another option is to fly an aircraft and take the photos yourself. I
have a PPG that I can fly over an area and take photos manually. Again
there are limitations there. Again, you have to stay out of the
restricted airspace where the big planes fly, a minimum altitude over
a built up area is required, and we're not allowed to take photos for
commercial purposes... OSM isn't commercial though...
Trying to photograph a city using these concepts is probably not a
good idea, but any of them could easily be used to photograph smaller
towns and villages where Google and Bing tend to ignore. I might have
to start overflying the towns around here next year and grabbing
aerial images for OSM!
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