Public Lab Research note


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Kite Mapping in Vancouver - Take 3

by MelissaN |

This research note is third in a series of research notes about my attempts as taking images in Vancouver, BC from a kite. You can read the previous research note here.

I really liked the Prism Stowaway kite that I lost due to kite string breakage during my first attempt at kite mapping, so I bought myself another one and made another attempt to capture some imagery from the sky. This time also had pretty strong winds, but having upgraded to 100 lb braided Dacron line ensured no kite lossage. Yay!

Being able to fold up the kite and stuff my kite in my backpack, I rode my bike to Vanier Park which is across False Creek from downtown and a popular place to fly kites.

One of my to-dos from my last attempt, was to confirm the very lax Canadian regulations on kite flying, which basically mean for un-moored kites, dont fly into cloud and in any way that endangers an aircraft. That's it. This means, you as a kiter with potentially no aviation knowledge, get to make judgement calls that affect the safety of passengers on aircraft. An email conversation with Transport Canada confirmed this. I think this is a pretty insane regulation however, since two sea planes flew very close to my kite string, at what I would guess to be about 500 feet - well underneath the height of my kite. There is a sea plane terminal a little over 2km away, so next time I go to Vanier Park to fly Kites, there is definitely going to be a call to air traffic control, or whoever is in charge of that airspace.

Unlike last time, Tina Time Lapse, the android app I was using to take pictures with, worked and I got about 450 pretty interesting pictures of part of downtown, Vanier Park, and Burrard Street Bridge.

The problem this time is that my attachment point for my camera rig slipped, so that all of the pictures are at an angle instead of straight down, which is ideal for mapping. Also, most images have distortion which I think is caused by slow shutter speeds, so next time I will experiment with the Sports 'Scene Mode' option (TTL has sparse documentation, so I am guessing that mode uses fast shutter speeds).

Lessons Learned

  • Explicitly setting shutter speeds is ideal to reduce image distortion
  • Canadian kite flying regulations are way too relaxed for the area I am flying my kite in
  • Letting the carabiner slide freely along the string that the camera rig hangs from means that the carabiner can get stuck in such a way that the camera is tilted and not able to capture images facing straight down

Next Steps

  • Test out Tina Time Lapse's Sports Scene Mode
  • Set Tina Time Lapse to focus on infinity to reduce any unnecessary effort required by the app during flight
  • Call air traffic control before flying kites at Vanier Park again
  • Make a loop on the string that attaches the camera rig to the kite to attach the carabiner so that the it cant slide and get stuck in an unwanted position.
  • Convince others to join me at kite mapping to make it more social, but also to enlist people to help reel the kite in, which takes at least 30 minutes and is a forearm workout.

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Downtown Vancouver, looking toward Burnaby.

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Granville Street Bridge.

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Burrard Street Bridge.

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Burrard Street Bridge, close up.

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Some boats in False Creek.

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A small piece of Vanier Park. Some pretty trees.



kite-mapping vancouver

6 Comments

Melissa,

Those photos are great. Good color and perfect exposure. The skewing adds much excitement, and adds a lot to my knowledge of phone cameras. Even though some of those photos were shot with very fast shutter speeds (e.g., faster than 1/700 second) there was still much distortion caused by the rolling shutter. This suggests that there is not much you can do about that when the camera is moving a lot. The image is constructed one line at a time and records the motion that happens during the scan. I am surprised that such fast shutter speeds showed so much motion, but the phone camera probably does not have an actual shutter, and maybe the electronic scan is not really as fast as it says it is (maybe each line gets exposed for 1/700 second, but the entire scan takes longer).

Most current phone cameras probably have similar CMOS sensors and rolling shutters and will produce similar results. Older point and shoot cameras used CCD sensors with global shutters so never show the skewing effect. Newer point and shoots have CMOS sensors, and some have rolling shutters, but the better ones seem to avoid the dramatic skewing somehow.

The ultimate solution is to avoid really windy days so the camera is not moving so much. It looks like it was rather windy that day. Lifting a camera does not require much wind, and less wind can mean less camera movement. The sweet spot of kite photography is "slack line" kiting, when the camera just floats. Even on such days, I usually lock the shutter speed high and let the aperture vary for correct exposure. Tina Timelapse was doing the opposite on your flight. The f-stop was always 2.6 (all the way open) and the shutter speed varied from slower than 1/300 second to faster than 1/700 second. But it would not have been possible for your phone to find a fast enough shutter speed to compensate for the camera motion that day.

The impressive thing is your commitment to figuring out how to do it and the fast progress you have made. It will be great to get others involved, but I applaud the approach of learning how to do it before trying to introduce others to the process. After three years of kite photography, I barely feel ready to show others how to do it. For example, I now know that windy days are NOT a good time to fly kites. A steady little breeze is all you need if you have the right kite. And it is SO much easier to reel it in (although it's still nice to have somebody to help).

Chris


Thanks Chris!

My default is to try and know what I am doing before involving other people, but I am actually pushing myself to make my kite-ing more social before then so that me and whoever else I can rope in can all fail together!

I will have to read up more on rolling shutters.

What kind of wind speeds does the steady little breeze have that you think is optimal? The day I was flying forecasted 5-20 km/h winds, and I am just in the process of learning what those numbers mean in real life and in relation to my kites, having paid no attention to them previously.

My favourite kite folds up which is a big bonus for me, but is only 5' wide. Do you think it will fly with a camera in the optimal breeze you recommend?


Do you have a link to your kite? There are apparently lots of Prism Stowaway kites.



"Flies super-stable at a high angle" Lol.


The forecast 5-20 km/hour wind is perfect for kite photography. From the looks of the flag and the foam streaks on the water in one of your photos, it seems like the wind was not below 15 km/hour (9 miles/hour) and maybe closer to 25 km/hour (15 miles/hour). The Stowaway Delta is a small kite for lifting a camera, so you need more wind than the typical KAP kite which can have twice the surface area and less than twice the weight of your Stowaway. So maybe you need a steady big breeze.

That kite should perform acceptably with a small camera in the right wind. To reduce camera motion, your next step might be a Picavet suspension. It can make a dramatic difference compared to hanging on a single string (is that what you did?). If there is enough wind, you could also try flying with tails which tend to steady the kite. Tails and Picavet lines increase the complexity (AKA tangles) somewhat severely. All the more reason to have helpers around.

I am not impressed that they sell that kite with 50 pound line. You paid handsomely for their poor judgement. I have never flown with less than 150 pound line.


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