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Question about taking aerial imagery.

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Offline johnv1983

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Question about taking aerial imagery.
« on: 20 / June / 2013, 14:05:10 »
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Greetings Folks,

I am new to this forum so I sincerely apologize if this topic has been covered but I'm in dire need of some help with CHDK. I am currently using an RC airplane to take aerial imagery. I've decided to use a Canon camera equipped with CHDK as my setup. I'm using a Canon PowerShot SX260 HS and I've got a 32gb SD cards loaded with CHDK. I am currently flying at an altitude of 75 meters and speeds of 14 meters per second. My only CHDK settings are a 1/640 shutter speed override and 3 second picture interval.

I am currently getting inconsistent imagery. Sometimes the images are too dark (cloudy day) and sometimes the picture quality isn't good enough to make it worth my time.

Does anybody have any ideas on how to set up my camera in order to obtain the highest quality (and most consistent) imagery possible.

Thank you very much!
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Offline Microfunguy

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Re: Question about taking aerial imagery.
« Reply #1 on: 20 / June / 2013, 14:25:11 »
Quote from: johnv1983 on 20 / June / 2013, 14:05:10
Does anybody have any ideas on how to set up my camera in order to obtain the highest quality (and most consistent) imagery possible.

Send me a message with an email address and I can put you in contact with someone who does this regularly.

I was particularly interested in the "accidental" stereo pairs that are produced, fascinating when panned and zoomed on a 3D TV.

David
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Offline reyalp

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Re: Question about taking aerial imagery.
« Reply #2 on: 20 / June / 2013, 16:55:55 »
Quote from: johnv1983 on 20 / June / 2013, 14:05:10
My only CHDK settings are a 1/640 shutter speed override and 3 second picture interval.
If you are overriding the shutter speed with CHDK, you probably need to calculate the rest of the exposure yourself. If you want the camera to do auto-exposure with a fixed Tv, you could use the cameras Tv mode. If you want to get a bit more sophisticated, you can write a script that adjusts exposure parameters within certain limits. Something like this script http://chdk.wikia.com/wiki/Drivelapse might be a good starting point.
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I am currently getting inconsistent imagery. Sometimes the images are too dark (cloudy day) and sometimes the picture quality isn't good enough to make it worth my time.
If you can give an example of how the quality is bad, we might be able to offer you better advice. You probably want to fix focus at infinity unless you are flying very low. The simplest way to do this would be using the cameras MF function to set it before flight.
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Offline andrewhazelden

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Re: Question about taking aerial imagery.
« Reply #3 on: 20 / June / 2013, 19:57:59 »
Hi Johnv1932.

Today I wrote a blog post that talks a bit about my experiences with CHDK and model airplane based aerial photography.

You will want to lock the focus to infinity (mountain mode) and set a CHDK shutter speed override to keep the exposure constant during a flight. A ND filter override can help too.

If it is a cloudy day you might need to increase your ISO setting to keep the photos from getting too dark.

Make sure you don't rigidly mount your camera to your model airplane's fuselage or you will transmit the vibrations from the electric motor into the camera body. You can dampen the vibrations by sticking a rubber pad between the camera body and the plane. Also make sure your propeller is balanced.

I have an aerial photography spreadsheet you might enjoy: Aerial_Imaging_Spreadsheet.xlsx



With the following settings you mentioned:
Airspeed 50.4 kph
Altitude 246 ft
shutter speed 1/640 sec

You will have minimum of a 2 pixel length motion blur on a 4kx3K resolution image before any camera vibration is factored in too.

You should try using a 1/2000th second shutter speed.
« Last Edit: 20 / June / 2013, 20:08:00 by andrewhazelden »
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Offline waterwingz

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Re: Question about taking aerial imagery.
« Reply #4 on: 20 / June / 2013, 23:33:21 »
@andrewhazelden   as you are obviously "someone who does this regularly",  thanks for sharing all this great detail here in the public forum !
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Offline johnv1983

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Re: Question about taking aerial imagery.
« Reply #5 on: 21 / June / 2013, 08:51:52 »
Thanks Andrew! You're spreadsheet will prove to be incredibly useful to me. I'll be sure to report back my results.
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Offline johnv1983

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Re: Question about taking aerial imagery.
« Reply #6 on: 21 / June / 2013, 09:13:43 »
Quote from: andrewhazelden on 20 / June / 2013, 19:57:59

You should try using a 1/2000th second shutter speed.

Quick question:

I'm worried about using this setting on a cloudy day. The ground is quite dark where I'm flying and I worry that the imagery will be far too dark using a 1/2000th shutter speed.
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Offline Microfunguy

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Re: Question about taking aerial imagery.
« Reply #7 on: 21 / June / 2013, 09:42:42 »
Quote from: johnv1983 on 21 / June / 2013, 09:13:43
I'm worried about using this setting on a cloudy day. The ground is quite dark where I'm flying and I worry that the imagery will be far too dark using a 1/2000th shutter speed.

Could well be.


You may have to use an ISO setting that you find unacceptable.

You can choose between low-noise blurred images or high noise sharper images  .. in such situations.

Some cameras are better than others at high ISO, they may also be heavier.

Decisions  .... decisions ....


David
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Offline andrewhazelden

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Re: Question about taking aerial imagery.
« Reply #8 on: 21 / June / 2013, 09:54:31 »
Hi Johnv1983.

With my SD780IS camera I get my best aerial photos on bright sunny days with the fastest shutter speeds possible.

If the weather is particularly cloudy or overcast I have to really boost the ISO settings a lot to get a bright enough photo without a lot of motion blur. This can make the photos grainer from the higher ISO setting.

Could you post a few of your aerial photos so I could see what the image quality is like?

If you're shooting with a slower shutter speed you might get some photos that are clear when the plane is heading into the wind, and other photos that are blurry when the plane is traveling back with the wind.

If you notice a difference in your photos when the motor is ON vs. when you are gliding for a bit then you might have a motor vibration issue too.
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Offline ThePara

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Re: Question about taking aerial imagery.
« Reply #9 on: 21 / June / 2013, 15:19:55 »
Maybe this is the proper thread to ask for help.

I'm doing aerial shoots with a CHDK'd A2200, using USB trigger and the live video feed via a wireless transmitter. I've tried to upgrade to an A4000, I've modified an HTC 11-pin USB connector to fit the Canon receptacle, tested the trigger and it works fine, but I'm unable to get a live video feed.

With the original Canon software, video-out switches from LCD to the connector pin only in playback mode.
I've looked through the "Property case" values hoping to find a variable for video feed ouput, but alas I couldn't find one.
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