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Camera Overlap

Posted: Mon Jan 29, 2018 10:37 am
by kramkroc
Hi folks,

one of the ninjas in our CoderDojo has been asking some interesting questions and I'll be honest and say that I'm stumped.

The main question he is asking is concerning the angle of view that the camera has, and how can we ensure that any photos taken don't overlap?


Re: Camera Overlap

Posted: Mon Jan 29, 2018 11:41 am
by Davespice
Good question!

So what you need to know about is something called ground sampling distance, or GSD for short. This the distance on ground represented by a single pixel of the camera. The Astro Pi training webinar says this is 161 meters per pixel.

This was calculated using this GSD calculator tool and plugging in the values from the camera data sheet for the V1 camera. Remember you have V2 in your Astro Pi kit, but V1 is on board the ISS. The altitude of the ISS was assumed to be 400 km.

So multiplying the GSD by the horizontal resolution (161 x 2592) gives you about 417 km, so that's the distance on ground between the left and right side of the image.

Have a read of this post which will give you an idea about how to trigger the camera based on target locations on ground, and you could employ a similar technique to ensure you only take a picture after the ISS travels every 417 km over the ground. You might also want to take into account vertical ground sampling distance for this though.

I hope this helps.


Re: Camera Overlap

Posted: Tue Jan 30, 2018 7:59 am
by kramkroc
Dave, I looked at that code and just wondered one thing. It calculates the location and whether there's an overlap and if it matches then it starts camera preview for 5 seconds before capturing the image. My point is with the 5 second camera warm up, have you not missed the boat, or sailed over the location you wanted to capture :D

Re: Camera Overlap

Posted: Tue Jan 30, 2018 10:03 am
by Davespice
Good observation, that would be a problem if the target just clips the edge of the field of view. But if moving through the middle you'll get 3 or 4 good pictures. I try not to give out perfect code so that people use it as a starting point and learn from it.

What you could do is have a greater trigger, say at 300 km, which starts the camera preview - and then go rapid fire capture when the distance to target is under 208 km.