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Affordable aerial photography
Aerial photography allows photographs to be taken from an elevated point and can be accomplished using a variety of techniques. These photos can then be stiched together using tools like Cartagen and Google Maps/Earth. The resulting images have a multitude of applications such as cartography, environmental studies and surveying, land use planning and other social justice projects.
Aerial photography can be achieved affordably using a helium filled balloons, simple mounting systems and a basic digital camera. This system was used to make maps with a community of Shipibo who have taken up residence on the bank of the river Rimac in downtown Lima - a city of 11 million people. Using only helium balloons and a cheap camera, the GrassrootsMapping.org team, part of the Center for Future Civic Media, took pictures of the extralegal settlement from approximately 500 feet up. The images were rectified and the resulting map will be used to help the Shipibo community in their legal battle to gain deeds to the land.
Basic materials List
- One balloon or as an alternative: 1 or 2 giant (95 gallon) trash bags and plastic packing tape
- Two 12” dowels, 1/4” diameter OR 1 2-liter plastic soda bottles
- 600 feet nylon string, like kite string
- Duct tape & clear packing tape
- An old canon camera
- Helium to fill the balloon to about a 5-foot diameter
Weather balloons can be kind of pricey, starting at ~$12 US dollars in packs of 2 (for 24 dollars total plus shipping) for a three foot wide balloon and 20 dollars plus shipping for an eight-foot balloon. You can compare prices here:
8 foot weather balloon from Edmund Scientifics ($24.95 each)
Buying big party balloons can be cheaper, at ~$6 per balloon, and three or four of them together can lift quite a bit. An added bonus is that if one balloon pops, you have a few more for a soft landing. You can also get them in beautiful red: 3 foot party balloons on Google Shopping ($4.85 each)
Finally, for the cheapest option, try giant trash bags: 95 gallon 2.7 mil trash bags (roll of 50 for $58.99)
Helium can be bought from Airgas if they’re nearby, or you can ask your local party store where they get theirs. A small tank of 60 cubic feet or so should be more than enough for several flights. 80 cubic feet cost ~$30.
Some great documentation on building this rig and using even hot air balloons can be found on Paul Illsley's Kite and Balloon Aerial Imaging site
You’ll need about 400 feet minimum of string. Either fishing line or nylon will do; I used a $3 roll of nylon string which is woven. I worry about the string getting caught on a building so I think the woven stuff is good - it can fray without breaking.
You’ll need a camera which can take pictures automatically every 10 seconds. Most Canon cameras can be used with the CHDK, a firmware hack which lets you run scripts off your SD card. Put this script in the scripts folder on the card once you’ve installed the CHDK.
It’s also worth it to set your shutter speed really high - like 1/500 or 1/1000. For a camera without shutter speed settings, turn up the ISO as high as it will go. This makes for grainy but still fairly sharp images. For the additional information concerning the settings of the camera you have, check the page for the specific model on the CHDK wiki.
If you have trouble with your camera turning off mid-flight, see the Chdk Issues page for suggestions… basically use new-ish batteries and fully charge them before flying.
Camera alternatives For more camera options, see Camera Options - it’s possible to use any Android phone which is easier though more expensive. Flip video cameras also work.
Your camera will bob and wave around in any amount of wind. Try to fly balloons only in minimal wind (less than 5mph) but if you do have bobbing and spinning you can stabilize things by using a Picavet suspension, which is made from a small wooden X (about a 30 cm across) with rings at each corner, and a kind of complicated string setup. Taping the camera to the center of the X can improve things a lot. See instructions for a Picavet suspension here.
Combining the images into a map
Cartagen Knitter can be used to ‘knit’ the images you’ve captured into a completed, georeferenced map. Once you’ve captured a bunch of photographs you’ll need to stitch them together. For help see the Cartagen Knitter help page.
Keep in mind that you’ll want a lot of images that overlap quite a bit, and that are generally pointing downward. The more sideways your images, the harder it’ll be to warp them and stitch them together.
The information on this page is modified from GrassrootsMapping.org a project which supports communities in cartographic dispute by creating low-cost mapping tools.